The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_bio.c

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    1 /*      $NetBSD: vfs_bio.c,v 1.142.2.1 2005/04/03 13:28:23 tron Exp $   */
    2 
    3 /*-
    4  * Copyright (c) 1982, 1986, 1989, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  * (c) UNIX System Laboratories, Inc.
    7  * All or some portions of this file are derived from material licensed
    8  * to the University of California by American Telephone and Telegraph
    9  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   10  * the permission of UNIX System Laboratories, Inc.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  * 3. Neither the name of the University nor the names of its contributors
   21  *    may be used to endorse or promote products derived from this software
   22  *    without specific prior written permission.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   34  * SUCH DAMAGE.
   35  *
   36  *      @(#)vfs_bio.c   8.6 (Berkeley) 1/11/94
   37  */
   38 
   39 /*-
   40  * Copyright (c) 1994 Christopher G. Demetriou
   41  *
   42  * Redistribution and use in source and binary forms, with or without
   43  * modification, are permitted provided that the following conditions
   44  * are met:
   45  * 1. Redistributions of source code must retain the above copyright
   46  *    notice, this list of conditions and the following disclaimer.
   47  * 2. Redistributions in binary form must reproduce the above copyright
   48  *    notice, this list of conditions and the following disclaimer in the
   49  *    documentation and/or other materials provided with the distribution.
   50  * 3. All advertising materials mentioning features or use of this software
   51  *    must display the following acknowledgement:
   52  *      This product includes software developed by the University of
   53  *      California, Berkeley and its contributors.
   54  * 4. Neither the name of the University nor the names of its contributors
   55  *    may be used to endorse or promote products derived from this software
   56  *    without specific prior written permission.
   57  *
   58  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   59  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   60  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   61  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   62  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   63  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   64  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   65  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   66  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   67  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   68  * SUCH DAMAGE.
   69  *
   70  *      @(#)vfs_bio.c   8.6 (Berkeley) 1/11/94
   71  */
   72 
   73 /*
   74  * Some references:
   75  *      Bach: The Design of the UNIX Operating System (Prentice Hall, 1986)
   76  *      Leffler, et al.: The Design and Implementation of the 4.3BSD
   77  *              UNIX Operating System (Addison Welley, 1989)
   78  */
   79 
   80 #include "opt_bufcache.h"
   81 #include "opt_softdep.h"
   82 
   83 #include <sys/cdefs.h>
   84 __KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.142.2.1 2005/04/03 13:28:23 tron Exp $");
   85 
   86 #include <sys/param.h>
   87 #include <sys/systm.h>
   88 #include <sys/kernel.h>
   89 #include <sys/proc.h>
   90 #include <sys/buf.h>
   91 #include <sys/vnode.h>
   92 #include <sys/mount.h>
   93 #include <sys/malloc.h>
   94 #include <sys/resourcevar.h>
   95 #include <sys/sysctl.h>
   96 #include <sys/conf.h>
   97 
   98 #include <uvm/uvm.h>
   99 
  100 #include <miscfs/specfs/specdev.h>
  101 
  102 #ifndef BUFPAGES
  103 # define BUFPAGES 0
  104 #endif
  105 
  106 #ifdef BUFCACHE
  107 # if (BUFCACHE < 5) || (BUFCACHE > 95)
  108 #  error BUFCACHE is not between 5 and 95
  109 # endif
  110 #else
  111 # define BUFCACHE 15
  112 #endif
  113 
  114 u_int   nbuf;                   /* XXX - for softdep_lockedbufs */
  115 u_int   bufpages = BUFPAGES;    /* optional hardwired count */
  116 u_int   bufcache = BUFCACHE;    /* max % of RAM to use for buffer cache */
  117 
  118 /* Function prototypes */
  119 struct bqueue;
  120 
  121 static void buf_setwm(void);
  122 static int buf_trim(void);
  123 static void *bufpool_page_alloc(struct pool *, int);
  124 static void bufpool_page_free(struct pool *, void *);
  125 static __inline struct buf *bio_doread(struct vnode *, daddr_t, int,
  126     struct ucred *, int);
  127 static int buf_lotsfree(void);
  128 static int buf_canrelease(void);
  129 static __inline u_long buf_mempoolidx(u_long);
  130 static __inline u_long buf_roundsize(u_long);
  131 static __inline caddr_t buf_malloc(size_t);
  132 static void buf_mrelease(caddr_t, size_t);
  133 static __inline void binsheadfree(struct buf *, struct bqueue *);
  134 static __inline void binstailfree(struct buf *, struct bqueue *);
  135 int count_lock_queue(void); /* XXX */
  136 #ifdef DEBUG
  137 static int checkfreelist(struct buf *, struct bqueue *);
  138 #endif
  139 
  140 /* Macros to clear/set/test flags. */
  141 #define SET(t, f)       (t) |= (f)
  142 #define CLR(t, f)       (t) &= ~(f)
  143 #define ISSET(t, f)     ((t) & (f))
  144 
  145 /*
  146  * Definitions for the buffer hash lists.
  147  */
  148 #define BUFHASH(dvp, lbn)       \
  149         (&bufhashtbl[(((long)(dvp) >> 8) + (int)(lbn)) & bufhash])
  150 LIST_HEAD(bufhashhdr, buf) *bufhashtbl, invalhash;
  151 u_long  bufhash;
  152 #if !defined(SOFTDEP) || !defined(FFS)
  153 struct bio_ops bioops;  /* I/O operation notification */
  154 #endif
  155 
  156 /*
  157  * Insq/Remq for the buffer hash lists.
  158  */
  159 #define binshash(bp, dp)        LIST_INSERT_HEAD(dp, bp, b_hash)
  160 #define bremhash(bp)            LIST_REMOVE(bp, b_hash)
  161 
  162 /*
  163  * Definitions for the buffer free lists.
  164  */
  165 #define BQUEUES         3               /* number of free buffer queues */
  166 
  167 #define BQ_LOCKED       0               /* super-blocks &c */
  168 #define BQ_LRU          1               /* lru, useful buffers */
  169 #define BQ_AGE          2               /* rubbish */
  170 
  171 struct bqueue {
  172         TAILQ_HEAD(, buf) bq_queue;
  173         uint64_t bq_bytes;
  174 } bufqueues[BQUEUES];
  175 int needbuffer;
  176 
  177 /*
  178  * Buffer queue lock.
  179  * Take this lock first if also taking some buffer's b_interlock.
  180  */
  181 struct simplelock bqueue_slock = SIMPLELOCK_INITIALIZER;
  182 
  183 /*
  184  * Buffer pool for I/O buffers.
  185  */
  186 struct pool bufpool;
  187 
  188 /* XXX - somewhat gross.. */
  189 #if MAXBSIZE == 0x2000
  190 #define NMEMPOOLS 4
  191 #elif MAXBSIZE == 0x4000
  192 #define NMEMPOOLS 5
  193 #elif MAXBSIZE == 0x8000
  194 #define NMEMPOOLS 6
  195 #else
  196 #define NMEMPOOLS 7
  197 #endif
  198 
  199 #define MEMPOOL_INDEX_OFFSET 10         /* smallest pool is 1k */
  200 #if (1 << (NMEMPOOLS + MEMPOOL_INDEX_OFFSET - 1)) != MAXBSIZE
  201 #error update vfs_bio buffer memory parameters
  202 #endif
  203 
  204 /* Buffer memory pools */
  205 static struct pool bmempools[NMEMPOOLS];
  206 
  207 struct vm_map *buf_map;
  208 
  209 /*
  210  * Buffer memory pool allocator.
  211  */
  212 static void *
  213 bufpool_page_alloc(struct pool *pp, int flags)
  214 {
  215 
  216         return (void *)uvm_km_kmemalloc1(buf_map,
  217             uvm.kernel_object, MAXBSIZE, MAXBSIZE, UVM_UNKNOWN_OFFSET,
  218             (flags & PR_WAITOK) ? 0 : UVM_KMF_NOWAIT | UVM_KMF_TRYLOCK);
  219 }
  220 
  221 static void
  222 bufpool_page_free(struct pool *pp, void *v)
  223 {
  224         uvm_km_free(buf_map, (vaddr_t)v, MAXBSIZE);
  225 }
  226 
  227 static struct pool_allocator bufmempool_allocator = {
  228         bufpool_page_alloc, bufpool_page_free, MAXBSIZE,
  229 };
  230 
  231 /* Buffer memory management variables */
  232 u_long bufmem_valimit;
  233 u_long bufmem_hiwater;
  234 u_long bufmem_lowater;
  235 u_long bufmem;
  236 
  237 /*
  238  * MD code can call this to set a hard limit on the amount
  239  * of virtual memory used by the buffer cache.
  240  */
  241 int
  242 buf_setvalimit(vsize_t sz)
  243 {
  244 
  245         /* We need to accommodate at least NMEMPOOLS of MAXBSIZE each */
  246         if (sz < NMEMPOOLS * MAXBSIZE)
  247                 return EINVAL;
  248 
  249         bufmem_valimit = sz;
  250         return 0;
  251 }
  252 
  253 static void
  254 buf_setwm(void)
  255 {
  256 
  257         bufmem_hiwater = buf_memcalc();
  258         /* lowater is approx. 2% of memory (with bufcache = 15) */
  259 #define BUFMEM_WMSHIFT  3
  260 #define BUFMEM_HIWMMIN  (64 * 1024 << BUFMEM_WMSHIFT)
  261         if (bufmem_hiwater < BUFMEM_HIWMMIN)
  262                 /* Ensure a reasonable minimum value */
  263                 bufmem_hiwater = BUFMEM_HIWMMIN;
  264         bufmem_lowater = bufmem_hiwater >> BUFMEM_WMSHIFT;
  265 }
  266 
  267 #ifdef DEBUG
  268 int debug_verify_freelist = 0;
  269 static int
  270 checkfreelist(struct buf *bp, struct bqueue *dp)
  271 {
  272         struct buf *b;
  273 
  274         TAILQ_FOREACH(b, &dp->bq_queue, b_freelist) {
  275                 if (b == bp)
  276                         return 1;
  277         }
  278         return 0;
  279 }
  280 #endif
  281 
  282 /*
  283  * Insq/Remq for the buffer hash lists.
  284  * Call with buffer queue locked.
  285  */
  286 static __inline void
  287 binsheadfree(struct buf *bp, struct bqueue *dp)
  288 {
  289 
  290         KASSERT(bp->b_freelistindex == -1);
  291         TAILQ_INSERT_HEAD(&dp->bq_queue, bp, b_freelist);
  292         dp->bq_bytes += bp->b_bufsize;
  293         bp->b_freelistindex = dp - bufqueues;
  294 }
  295 
  296 static __inline void
  297 binstailfree(struct buf *bp, struct bqueue *dp)
  298 {
  299 
  300         KASSERT(bp->b_freelistindex == -1);
  301         TAILQ_INSERT_TAIL(&dp->bq_queue, bp, b_freelist);
  302         dp->bq_bytes += bp->b_bufsize;
  303         bp->b_freelistindex = dp - bufqueues;
  304 }
  305 
  306 void
  307 bremfree(struct buf *bp)
  308 {
  309         struct bqueue *dp;
  310         int bqidx = bp->b_freelistindex;
  311 
  312         LOCK_ASSERT(simple_lock_held(&bqueue_slock));
  313 
  314         KASSERT(bqidx != -1);
  315         dp = &bufqueues[bqidx];
  316         KDASSERT(!debug_verify_freelist || checkfreelist(bp, dp));
  317         KASSERT(dp->bq_bytes >= bp->b_bufsize);
  318         TAILQ_REMOVE(&dp->bq_queue, bp, b_freelist);
  319         dp->bq_bytes -= bp->b_bufsize;
  320 #if defined(DIAGNOSTIC)
  321         bp->b_freelistindex = -1;
  322 #endif /* defined(DIAGNOSTIC) */
  323 }
  324 
  325 u_long
  326 buf_memcalc(void)
  327 {
  328         u_long n;
  329 
  330         /*
  331          * Determine the upper bound of memory to use for buffers.
  332          *
  333          *      - If bufpages is specified, use that as the number
  334          *        pages.
  335          *
  336          *      - Otherwise, use bufcache as the percentage of
  337          *        physical memory.
  338          */
  339         if (bufpages != 0) {
  340                 n = bufpages;
  341         } else {
  342                 if (bufcache < 5) {
  343                         printf("forcing bufcache %d -> 5", bufcache);
  344                         bufcache = 5;
  345                 }
  346                 if (bufcache > 95) {
  347                         printf("forcing bufcache %d -> 95", bufcache);
  348                         bufcache = 95;
  349                 }
  350                 n = physmem / 100 * bufcache;
  351         }
  352 
  353         n <<= PAGE_SHIFT;
  354         if (bufmem_valimit != 0 && n > bufmem_valimit)
  355                 n = bufmem_valimit;
  356 
  357         return (n);
  358 }
  359 
  360 /*
  361  * Initialize buffers and hash links for buffers.
  362  */
  363 void
  364 bufinit(void)
  365 {
  366         struct bqueue *dp;
  367         int use_std;
  368         u_int i;
  369 
  370         /*
  371          * Initialize buffer cache memory parameters.
  372          */
  373         bufmem = 0;
  374         buf_setwm();
  375 
  376         if (bufmem_valimit != 0) {
  377                 vaddr_t minaddr = 0, maxaddr;
  378                 buf_map = uvm_km_suballoc(kernel_map, &minaddr, &maxaddr,
  379                                           bufmem_valimit, VM_MAP_PAGEABLE,
  380                                           FALSE, 0);
  381                 if (buf_map == NULL)
  382                         panic("bufinit: cannot allocate submap");
  383         } else
  384                 buf_map = kernel_map;
  385 
  386         /*
  387          * Initialize the buffer pools.
  388          */
  389         pool_init(&bufpool, sizeof(struct buf), 0, 0, 0, "bufpl", NULL);
  390 
  391         /* On "small" machines use small pool page sizes where possible */
  392         use_std = (physmem < atop(16*1024*1024));
  393 
  394         /*
  395          * Also use them on systems that can map the pool pages using
  396          * a direct-mapped segment.
  397          */
  398 #ifdef PMAP_MAP_POOLPAGE
  399         use_std = 1;
  400 #endif
  401 
  402         for (i = 0; i < NMEMPOOLS; i++) {
  403                 struct pool_allocator *pa;
  404                 struct pool *pp = &bmempools[i];
  405                 u_int size = 1 << (i + MEMPOOL_INDEX_OFFSET);
  406                 char *name = malloc(8, M_TEMP, M_WAITOK);
  407                 snprintf(name, 8, "buf%dk", 1 << i);
  408                 pa = (size <= PAGE_SIZE && use_std)
  409                         ? &pool_allocator_nointr
  410                         : &bufmempool_allocator;
  411                 pool_init(pp, size, 0, 0, 0, name, pa);
  412                 pool_setlowat(pp, 1);
  413                 pool_sethiwat(pp, 1);
  414         }
  415 
  416         /* Initialize the buffer queues */
  417         for (dp = bufqueues; dp < &bufqueues[BQUEUES]; dp++) {
  418                 TAILQ_INIT(&dp->bq_queue);
  419                 dp->bq_bytes = 0;
  420         }
  421 
  422         /*
  423          * Estimate hash table size based on the amount of memory we
  424          * intend to use for the buffer cache. The average buffer
  425          * size is dependent on our clients (i.e. filesystems).
  426          *
  427          * For now, use an empirical 3K per buffer.
  428          */
  429         nbuf = (bufmem_hiwater / 1024) / 3;
  430         bufhashtbl = hashinit(nbuf, HASH_LIST, M_CACHE, M_WAITOK, &bufhash);
  431 }
  432 
  433 static int
  434 buf_lotsfree(void)
  435 {
  436         int try, thresh;
  437         struct lwp *l = curlwp;
  438 
  439         /* Always allocate if doing copy on write */
  440         if (l->l_flag & L_COWINPROGRESS)
  441                 return 1;
  442 
  443         /* Always allocate if less than the low water mark. */
  444         if (bufmem < bufmem_lowater)
  445                 return 1;
  446 
  447         /* Never allocate if greater than the high water mark. */
  448         if (bufmem > bufmem_hiwater)
  449                 return 0;
  450 
  451         /* If there's anything on the AGE list, it should be eaten. */
  452         if (TAILQ_FIRST(&bufqueues[BQ_AGE].bq_queue) != NULL)
  453                 return 0;
  454 
  455         /*
  456          * The probabily of getting a new allocation is inversely
  457          * proportional to the current size of the cache, using
  458          * a granularity of 16 steps.
  459          */
  460         try = random() & 0x0000000fL;
  461 
  462         /* Don't use "16 * bufmem" here to avoid a 32-bit overflow. */
  463         thresh = (bufmem - bufmem_lowater) /
  464             ((bufmem_hiwater - bufmem_lowater) / 16);
  465 
  466         if (try >= thresh)
  467                 return 1;
  468 
  469         /* Otherwise don't allocate. */
  470         return 0;
  471 }
  472 
  473 /*
  474  * Return estimate of bytes we think need to be
  475  * released to help resolve low memory conditions.
  476  *
  477  * => called at splbio.
  478  * => called with bqueue_slock held.
  479  */
  480 static int
  481 buf_canrelease(void)
  482 {
  483         int pagedemand, ninvalid = 0;
  484 
  485         LOCK_ASSERT(simple_lock_held(&bqueue_slock));
  486 
  487         if (bufmem < bufmem_lowater)
  488                 return 0;
  489 
  490         if (bufmem > bufmem_hiwater)
  491                 return bufmem - bufmem_hiwater;
  492 
  493         ninvalid += bufqueues[BQ_AGE].bq_bytes;
  494 
  495         pagedemand = uvmexp.freetarg - uvmexp.free;
  496         if (pagedemand < 0)
  497                 return ninvalid;
  498         return MAX(ninvalid, MIN(2 * MAXBSIZE,
  499             MIN((bufmem - bufmem_lowater) / 16, pagedemand * PAGE_SIZE)));
  500 }
  501 
  502 /*
  503  * Buffer memory allocation helper functions
  504  */
  505 static __inline u_long
  506 buf_mempoolidx(u_long size)
  507 {
  508         u_int n = 0;
  509 
  510         size -= 1;
  511         size >>= MEMPOOL_INDEX_OFFSET;
  512         while (size) {
  513                 size >>= 1;
  514                 n += 1;
  515         }
  516         if (n >= NMEMPOOLS)
  517                 panic("buf mem pool index %d", n);
  518         return n;
  519 }
  520 
  521 static __inline u_long
  522 buf_roundsize(u_long size)
  523 {
  524         /* Round up to nearest power of 2 */
  525         return (1 << (buf_mempoolidx(size) + MEMPOOL_INDEX_OFFSET));
  526 }
  527 
  528 static __inline caddr_t
  529 buf_malloc(size_t size)
  530 {
  531         u_int n = buf_mempoolidx(size);
  532         caddr_t addr;
  533         int s;
  534 
  535         while (1) {
  536                 addr = pool_get(&bmempools[n], PR_NOWAIT);
  537                 if (addr != NULL)
  538                         break;
  539 
  540                 /* No memory, see if we can free some. If so, try again */
  541                 if (buf_drain(1) > 0)
  542                         continue;
  543 
  544                 /* Wait for buffers to arrive on the LRU queue */
  545                 s = splbio();
  546                 simple_lock(&bqueue_slock);
  547                 needbuffer = 1;
  548                 ltsleep(&needbuffer, PNORELOCK | (PRIBIO + 1),
  549                         "buf_malloc", 0, &bqueue_slock);
  550                 splx(s);
  551         }
  552 
  553         return addr;
  554 }
  555 
  556 static void
  557 buf_mrelease(caddr_t addr, size_t size)
  558 {
  559 
  560         pool_put(&bmempools[buf_mempoolidx(size)], addr);
  561 }
  562 
  563 /*
  564  * bread()/breadn() helper.
  565  */
  566 static __inline struct buf *
  567 bio_doread(struct vnode *vp, daddr_t blkno, int size, struct ucred *cred,
  568     int async)
  569 {
  570         struct buf *bp;
  571         struct lwp *l  = (curlwp != NULL ? curlwp : &lwp0);     /* XXX */
  572         struct proc *p = l->l_proc;
  573         struct mount *mp;
  574 
  575         bp = getblk(vp, blkno, size, 0, 0);
  576 
  577 #ifdef DIAGNOSTIC
  578         if (bp == NULL) {
  579                 panic("bio_doread: no such buf");
  580         }
  581 #endif
  582 
  583         /*
  584          * If buffer does not have data valid, start a read.
  585          * Note that if buffer is B_INVAL, getblk() won't return it.
  586          * Therefore, it's valid if its I/O has completed or been delayed.
  587          */
  588         if (!ISSET(bp->b_flags, (B_DONE | B_DELWRI))) {
  589                 /* Start I/O for the buffer. */
  590                 SET(bp->b_flags, B_READ | async);
  591                 if (async)
  592                         BIO_SETPRIO(bp, BPRIO_TIMELIMITED);
  593                 else
  594                         BIO_SETPRIO(bp, BPRIO_TIMECRITICAL);
  595                 VOP_STRATEGY(vp, bp);
  596 
  597                 /* Pay for the read. */
  598                 p->p_stats->p_ru.ru_inblock++;
  599         } else if (async) {
  600                 brelse(bp);
  601         }
  602 
  603         if (vp->v_type == VBLK)
  604                 mp = vp->v_specmountpoint;
  605         else
  606                 mp = vp->v_mount;
  607 
  608         /*
  609          * Collect statistics on synchronous and asynchronous reads.
  610          * Reads from block devices are charged to their associated
  611          * filesystem (if any).
  612          */
  613         if (mp != NULL) {
  614                 if (async == 0)
  615                         mp->mnt_stat.f_syncreads++;
  616                 else
  617                         mp->mnt_stat.f_asyncreads++;
  618         }
  619 
  620         return (bp);
  621 }
  622 
  623 /*
  624  * Read a disk block.
  625  * This algorithm described in Bach (p.54).
  626  */
  627 int
  628 bread(struct vnode *vp, daddr_t blkno, int size, struct ucred *cred,
  629     struct buf **bpp)
  630 {
  631         struct buf *bp;
  632 
  633         /* Get buffer for block. */
  634         bp = *bpp = bio_doread(vp, blkno, size, cred, 0);
  635 
  636         /* Wait for the read to complete, and return result. */
  637         return (biowait(bp));
  638 }
  639 
  640 /*
  641  * Read-ahead multiple disk blocks. The first is sync, the rest async.
  642  * Trivial modification to the breada algorithm presented in Bach (p.55).
  643  */
  644 int
  645 breadn(struct vnode *vp, daddr_t blkno, int size, daddr_t *rablks,
  646     int *rasizes, int nrablks, struct ucred *cred, struct buf **bpp)
  647 {
  648         struct buf *bp;
  649         int i;
  650 
  651         bp = *bpp = bio_doread(vp, blkno, size, cred, 0);
  652 
  653         /*
  654          * For each of the read-ahead blocks, start a read, if necessary.
  655          */
  656         for (i = 0; i < nrablks; i++) {
  657                 /* If it's in the cache, just go on to next one. */
  658                 if (incore(vp, rablks[i]))
  659                         continue;
  660 
  661                 /* Get a buffer for the read-ahead block */
  662                 (void) bio_doread(vp, rablks[i], rasizes[i], cred, B_ASYNC);
  663         }
  664 
  665         /* Otherwise, we had to start a read for it; wait until it's valid. */
  666         return (biowait(bp));
  667 }
  668 
  669 /*
  670  * Read with single-block read-ahead.  Defined in Bach (p.55), but
  671  * implemented as a call to breadn().
  672  * XXX for compatibility with old file systems.
  673  */
  674 int
  675 breada(struct vnode *vp, daddr_t blkno, int size, daddr_t rablkno,
  676     int rabsize, struct ucred *cred, struct buf **bpp)
  677 {
  678 
  679         return (breadn(vp, blkno, size, &rablkno, &rabsize, 1, cred, bpp));
  680 }
  681 
  682 /*
  683  * Block write.  Described in Bach (p.56)
  684  */
  685 int
  686 bwrite(struct buf *bp)
  687 {
  688         int rv, sync, wasdelayed, s;
  689         struct lwp *l  = (curlwp != NULL ? curlwp : &lwp0);     /* XXX */
  690         struct proc *p = l->l_proc;
  691         struct vnode *vp;
  692         struct mount *mp;
  693 
  694         KASSERT(ISSET(bp->b_flags, B_BUSY));
  695 
  696         vp = bp->b_vp;
  697         if (vp != NULL) {
  698                 if (vp->v_type == VBLK)
  699                         mp = vp->v_specmountpoint;
  700                 else
  701                         mp = vp->v_mount;
  702         } else {
  703                 mp = NULL;
  704         }
  705 
  706         /*
  707          * Remember buffer type, to switch on it later.  If the write was
  708          * synchronous, but the file system was mounted with MNT_ASYNC,
  709          * convert it to a delayed write.
  710          * XXX note that this relies on delayed tape writes being converted
  711          * to async, not sync writes (which is safe, but ugly).
  712          */
  713         sync = !ISSET(bp->b_flags, B_ASYNC);
  714         if (sync && mp != NULL && ISSET(mp->mnt_flag, MNT_ASYNC)) {
  715                 bdwrite(bp);
  716                 return (0);
  717         }
  718 
  719         /*
  720          * Collect statistics on synchronous and asynchronous writes.
  721          * Writes to block devices are charged to their associated
  722          * filesystem (if any).
  723          */
  724         if (mp != NULL) {
  725                 if (sync)
  726                         mp->mnt_stat.f_syncwrites++;
  727                 else
  728                         mp->mnt_stat.f_asyncwrites++;
  729         }
  730 
  731         s = splbio();
  732         simple_lock(&bp->b_interlock);
  733 
  734         wasdelayed = ISSET(bp->b_flags, B_DELWRI);
  735 
  736         CLR(bp->b_flags, (B_READ | B_DONE | B_ERROR | B_DELWRI));
  737 
  738         /*
  739          * Pay for the I/O operation and make sure the buf is on the correct
  740          * vnode queue.
  741          */
  742         if (wasdelayed)
  743                 reassignbuf(bp, bp->b_vp);
  744         else
  745                 p->p_stats->p_ru.ru_oublock++;
  746 
  747         /* Initiate disk write.  Make sure the appropriate party is charged. */
  748         V_INCR_NUMOUTPUT(bp->b_vp);
  749         simple_unlock(&bp->b_interlock);
  750         splx(s);
  751 
  752         if (sync)
  753                 BIO_SETPRIO(bp, BPRIO_TIMECRITICAL);
  754         else
  755                 BIO_SETPRIO(bp, BPRIO_TIMELIMITED);
  756 
  757         VOP_STRATEGY(vp, bp);
  758 
  759         if (sync) {
  760                 /* If I/O was synchronous, wait for it to complete. */
  761                 rv = biowait(bp);
  762 
  763                 /* Release the buffer. */
  764                 brelse(bp);
  765 
  766                 return (rv);
  767         } else {
  768                 return (0);
  769         }
  770 }
  771 
  772 int
  773 vn_bwrite(void *v)
  774 {
  775         struct vop_bwrite_args *ap = v;
  776 
  777         return (bwrite(ap->a_bp));
  778 }
  779 
  780 /*
  781  * Delayed write.
  782  *
  783  * The buffer is marked dirty, but is not queued for I/O.
  784  * This routine should be used when the buffer is expected
  785  * to be modified again soon, typically a small write that
  786  * partially fills a buffer.
  787  *
  788  * NB: magnetic tapes cannot be delayed; they must be
  789  * written in the order that the writes are requested.
  790  *
  791  * Described in Leffler, et al. (pp. 208-213).
  792  */
  793 void
  794 bdwrite(struct buf *bp)
  795 {
  796         struct lwp *l  = (curlwp != NULL ? curlwp : &lwp0);     /* XXX */
  797         struct proc *p = l->l_proc;
  798         const struct bdevsw *bdev;
  799         int s;
  800 
  801         /* If this is a tape block, write the block now. */
  802         bdev = bdevsw_lookup(bp->b_dev);
  803         if (bdev != NULL && bdev->d_type == D_TAPE) {
  804                 bawrite(bp);
  805                 return;
  806         }
  807 
  808         /*
  809          * If the block hasn't been seen before:
  810          *      (1) Mark it as having been seen,
  811          *      (2) Charge for the write,
  812          *      (3) Make sure it's on its vnode's correct block list.
  813          */
  814         s = splbio();
  815         simple_lock(&bp->b_interlock);
  816 
  817         KASSERT(ISSET(bp->b_flags, B_BUSY));
  818 
  819         if (!ISSET(bp->b_flags, B_DELWRI)) {
  820                 SET(bp->b_flags, B_DELWRI);
  821                 p->p_stats->p_ru.ru_oublock++;
  822                 reassignbuf(bp, bp->b_vp);
  823         }
  824 
  825         /* Otherwise, the "write" is done, so mark and release the buffer. */
  826         CLR(bp->b_flags, B_DONE);
  827         simple_unlock(&bp->b_interlock);
  828         splx(s);
  829 
  830         brelse(bp);
  831 }
  832 
  833 /*
  834  * Asynchronous block write; just an asynchronous bwrite().
  835  */
  836 void
  837 bawrite(struct buf *bp)
  838 {
  839         int s;
  840 
  841         s = splbio();
  842         simple_lock(&bp->b_interlock);
  843 
  844         KASSERT(ISSET(bp->b_flags, B_BUSY));
  845 
  846         SET(bp->b_flags, B_ASYNC);
  847         simple_unlock(&bp->b_interlock);
  848         splx(s);
  849         VOP_BWRITE(bp);
  850 }
  851 
  852 /*
  853  * Same as first half of bdwrite, mark buffer dirty, but do not release it.
  854  * Call at splbio() and with the buffer interlock locked.
  855  * Note: called only from biodone() through ffs softdep's bioops.io_complete()
  856  */
  857 void
  858 bdirty(struct buf *bp)
  859 {
  860         struct lwp *l  = (curlwp != NULL ? curlwp : &lwp0);     /* XXX */
  861         struct proc *p = l->l_proc;
  862 
  863         LOCK_ASSERT(simple_lock_held(&bp->b_interlock));
  864         KASSERT(ISSET(bp->b_flags, B_BUSY));
  865 
  866         CLR(bp->b_flags, B_AGE);
  867 
  868         if (!ISSET(bp->b_flags, B_DELWRI)) {
  869                 SET(bp->b_flags, B_DELWRI);
  870                 p->p_stats->p_ru.ru_oublock++;
  871                 reassignbuf(bp, bp->b_vp);
  872         }
  873 }
  874 
  875 /*
  876  * Release a buffer on to the free lists.
  877  * Described in Bach (p. 46).
  878  */
  879 void
  880 brelse(struct buf *bp)
  881 {
  882         struct bqueue *bufq;
  883         int s;
  884 
  885         /* Block disk interrupts. */
  886         s = splbio();
  887         simple_lock(&bqueue_slock);
  888         simple_lock(&bp->b_interlock);
  889 
  890         KASSERT(ISSET(bp->b_flags, B_BUSY));
  891         KASSERT(!ISSET(bp->b_flags, B_CALL));
  892 
  893         /* Wake up any processes waiting for any buffer to become free. */
  894         if (needbuffer) {
  895                 needbuffer = 0;
  896                 wakeup(&needbuffer);
  897         }
  898 
  899         /* Wake up any proceeses waiting for _this_ buffer to become free. */
  900         if (ISSET(bp->b_flags, B_WANTED)) {
  901                 CLR(bp->b_flags, B_WANTED|B_AGE);
  902                 wakeup(bp);
  903         }
  904 
  905         /*
  906          * Determine which queue the buffer should be on, then put it there.
  907          */
  908 
  909         /* If it's locked, don't report an error; try again later. */
  910         if (ISSET(bp->b_flags, (B_LOCKED|B_ERROR)) == (B_LOCKED|B_ERROR))
  911                 CLR(bp->b_flags, B_ERROR);
  912 
  913         /* If it's not cacheable, or an error, mark it invalid. */
  914         if (ISSET(bp->b_flags, (B_NOCACHE|B_ERROR)))
  915                 SET(bp->b_flags, B_INVAL);
  916 
  917         if (ISSET(bp->b_flags, B_VFLUSH)) {
  918                 /*
  919                  * This is a delayed write buffer that was just flushed to
  920                  * disk.  It is still on the LRU queue.  If it's become
  921                  * invalid, then we need to move it to a different queue;
  922                  * otherwise leave it in its current position.
  923                  */
  924                 CLR(bp->b_flags, B_VFLUSH);
  925                 if (!ISSET(bp->b_flags, B_ERROR|B_INVAL|B_LOCKED|B_AGE)) {
  926                         KDASSERT(!debug_verify_freelist || checkfreelist(bp, &bufqueues[BQ_LRU]));
  927                         goto already_queued;
  928                 } else {
  929                         bremfree(bp);
  930                 }
  931         }
  932 
  933   KDASSERT(!debug_verify_freelist || !checkfreelist(bp, &bufqueues[BQ_AGE]));
  934   KDASSERT(!debug_verify_freelist || !checkfreelist(bp, &bufqueues[BQ_LRU]));
  935   KDASSERT(!debug_verify_freelist || !checkfreelist(bp, &bufqueues[BQ_LOCKED]));
  936 
  937         if ((bp->b_bufsize <= 0) || ISSET(bp->b_flags, B_INVAL)) {
  938                 /*
  939                  * If it's invalid or empty, dissociate it from its vnode
  940                  * and put on the head of the appropriate queue.
  941                  */
  942                 if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_deallocate)
  943                         (*bioops.io_deallocate)(bp);
  944                 CLR(bp->b_flags, B_DONE|B_DELWRI);
  945                 if (bp->b_vp) {
  946                         reassignbuf(bp, bp->b_vp);
  947                         brelvp(bp);
  948                 }
  949                 if (bp->b_bufsize <= 0)
  950                         /* no data */
  951                         goto already_queued;
  952                 else
  953                         /* invalid data */
  954                         bufq = &bufqueues[BQ_AGE];
  955                 binsheadfree(bp, bufq);
  956         } else {
  957                 /*
  958                  * It has valid data.  Put it on the end of the appropriate
  959                  * queue, so that it'll stick around for as long as possible.
  960                  * If buf is AGE, but has dependencies, must put it on last
  961                  * bufqueue to be scanned, ie LRU. This protects against the
  962                  * livelock where BQ_AGE only has buffers with dependencies,
  963                  * and we thus never get to the dependent buffers in BQ_LRU.
  964                  */
  965                 if (ISSET(bp->b_flags, B_LOCKED))
  966                         /* locked in core */
  967                         bufq = &bufqueues[BQ_LOCKED];
  968                 else if (!ISSET(bp->b_flags, B_AGE))
  969                         /* valid data */
  970                         bufq = &bufqueues[BQ_LRU];
  971                 else {
  972                         /* stale but valid data */
  973                         int has_deps;
  974 
  975                         if (LIST_FIRST(&bp->b_dep) != NULL &&
  976                             bioops.io_countdeps)
  977                                 has_deps = (*bioops.io_countdeps)(bp, 0);
  978                         else
  979                                 has_deps = 0;
  980                         bufq = has_deps ? &bufqueues[BQ_LRU] :
  981                             &bufqueues[BQ_AGE];
  982                 }
  983                 binstailfree(bp, bufq);
  984         }
  985 
  986 already_queued:
  987         /* Unlock the buffer. */
  988         CLR(bp->b_flags, B_AGE|B_ASYNC|B_BUSY|B_NOCACHE);
  989         SET(bp->b_flags, B_CACHE);
  990 
  991         /* Allow disk interrupts. */
  992         simple_unlock(&bp->b_interlock);
  993         simple_unlock(&bqueue_slock);
  994         if (bp->b_bufsize <= 0) {
  995 #ifdef DEBUG
  996                 memset((char *)bp, 0, sizeof(*bp));
  997 #endif
  998                 pool_put(&bufpool, bp);
  999         }
 1000         splx(s);
 1001 }
 1002 
 1003 /*
 1004  * Determine if a block is in the cache.
 1005  * Just look on what would be its hash chain.  If it's there, return
 1006  * a pointer to it, unless it's marked invalid.  If it's marked invalid,
 1007  * we normally don't return the buffer, unless the caller explicitly
 1008  * wants us to.
 1009  */
 1010 struct buf *
 1011 incore(struct vnode *vp, daddr_t blkno)
 1012 {
 1013         struct buf *bp;
 1014 
 1015         /* Search hash chain */
 1016         LIST_FOREACH(bp, BUFHASH(vp, blkno), b_hash) {
 1017                 if (bp->b_lblkno == blkno && bp->b_vp == vp &&
 1018                     !ISSET(bp->b_flags, B_INVAL))
 1019                 return (bp);
 1020         }
 1021 
 1022         return (NULL);
 1023 }
 1024 
 1025 /*
 1026  * Get a block of requested size that is associated with
 1027  * a given vnode and block offset. If it is found in the
 1028  * block cache, mark it as having been found, make it busy
 1029  * and return it. Otherwise, return an empty block of the
 1030  * correct size. It is up to the caller to insure that the
 1031  * cached blocks be of the correct size.
 1032  */
 1033 struct buf *
 1034 getblk(struct vnode *vp, daddr_t blkno, int size, int slpflag, int slptimeo)
 1035 {
 1036         struct buf *bp;
 1037         int s, err;
 1038         int preserve;
 1039 
 1040 start:
 1041         s = splbio();
 1042         simple_lock(&bqueue_slock);
 1043         bp = incore(vp, blkno);
 1044         if (bp != NULL) {
 1045                 simple_lock(&bp->b_interlock);
 1046                 if (ISSET(bp->b_flags, B_BUSY)) {
 1047                         simple_unlock(&bqueue_slock);
 1048                         if (curproc == uvm.pagedaemon_proc) {
 1049                                 simple_unlock(&bp->b_interlock);
 1050                                 splx(s);
 1051                                 return NULL;
 1052                         }
 1053                         SET(bp->b_flags, B_WANTED);
 1054                         err = ltsleep(bp, slpflag | (PRIBIO + 1) | PNORELOCK,
 1055                                         "getblk", slptimeo, &bp->b_interlock);
 1056                         splx(s);
 1057                         if (err)
 1058                                 return (NULL);
 1059                         goto start;
 1060                 }
 1061 #ifdef DIAGNOSTIC
 1062                 if (ISSET(bp->b_flags, B_DONE|B_DELWRI) &&
 1063                     bp->b_bcount < size && vp->v_type != VBLK)
 1064                         panic("getblk: block size invariant failed");
 1065 #endif
 1066                 SET(bp->b_flags, B_BUSY);
 1067                 bremfree(bp);
 1068                 preserve = 1;
 1069         } else {
 1070                 if ((bp = getnewbuf(slpflag, slptimeo, 0)) == NULL) {
 1071                         simple_unlock(&bqueue_slock);
 1072                         splx(s);
 1073                         goto start;
 1074                 }
 1075 
 1076                 binshash(bp, BUFHASH(vp, blkno));
 1077                 bp->b_blkno = bp->b_lblkno = bp->b_rawblkno = blkno;
 1078                 bgetvp(vp, bp);
 1079                 preserve = 0;
 1080         }
 1081         simple_unlock(&bp->b_interlock);
 1082         simple_unlock(&bqueue_slock);
 1083         splx(s);
 1084         /*
 1085          * LFS can't track total size of B_LOCKED buffer (locked_queue_bytes)
 1086          * if we re-size buffers here.
 1087          */
 1088         if (ISSET(bp->b_flags, B_LOCKED)) {
 1089                 KASSERT(bp->b_bufsize >= size);
 1090         } else {
 1091                 allocbuf(bp, size, preserve);
 1092         }
 1093         BIO_SETPRIO(bp, BPRIO_DEFAULT);
 1094         return (bp);
 1095 }
 1096 
 1097 /*
 1098  * Get an empty, disassociated buffer of given size.
 1099  */
 1100 struct buf *
 1101 geteblk(int size)
 1102 {
 1103         struct buf *bp;
 1104         int s;
 1105 
 1106         s = splbio();
 1107         simple_lock(&bqueue_slock);
 1108         while ((bp = getnewbuf(0, 0, 0)) == 0)
 1109                 ;
 1110 
 1111         SET(bp->b_flags, B_INVAL);
 1112         binshash(bp, &invalhash);
 1113         simple_unlock(&bqueue_slock);
 1114         simple_unlock(&bp->b_interlock);
 1115         splx(s);
 1116         BIO_SETPRIO(bp, BPRIO_DEFAULT);
 1117         allocbuf(bp, size, 0);
 1118         return (bp);
 1119 }
 1120 
 1121 /*
 1122  * Expand or contract the actual memory allocated to a buffer.
 1123  *
 1124  * If the buffer shrinks, data is lost, so it's up to the
 1125  * caller to have written it out *first*; this routine will not
 1126  * start a write.  If the buffer grows, it's the callers
 1127  * responsibility to fill out the buffer's additional contents.
 1128  */
 1129 void
 1130 allocbuf(struct buf *bp, int size, int preserve)
 1131 {
 1132         vsize_t oldsize, desired_size;
 1133         caddr_t addr;
 1134         int s, delta;
 1135 
 1136         desired_size = buf_roundsize(size);
 1137         if (desired_size > MAXBSIZE)
 1138                 printf("allocbuf: buffer larger than MAXBSIZE requested");
 1139 
 1140         bp->b_bcount = size;
 1141 
 1142         oldsize = bp->b_bufsize;
 1143         if (oldsize == desired_size)
 1144                 return;
 1145 
 1146         /*
 1147          * If we want a buffer of a different size, re-allocate the
 1148          * buffer's memory; copy old content only if needed.
 1149          */
 1150         addr = buf_malloc(desired_size);
 1151         if (preserve)
 1152                 memcpy(addr, bp->b_data, MIN(oldsize,desired_size));
 1153         if (bp->b_data != NULL)
 1154                 buf_mrelease(bp->b_data, oldsize);
 1155         bp->b_data = addr;
 1156         bp->b_bufsize = desired_size;
 1157 
 1158         /*
 1159          * Update overall buffer memory counter (protected by bqueue_slock)
 1160          */
 1161         delta = (long)desired_size - (long)oldsize;
 1162 
 1163         s = splbio();
 1164         simple_lock(&bqueue_slock);
 1165         if ((bufmem += delta) > bufmem_hiwater) {
 1166                 /*
 1167                  * Need to trim overall memory usage.
 1168                  */
 1169                 while (buf_canrelease()) {
 1170                         if (buf_trim() == 0)
 1171                                 break;
 1172                 }
 1173         }
 1174 
 1175         simple_unlock(&bqueue_slock);
 1176         splx(s);
 1177 }
 1178 
 1179 /*
 1180  * Find a buffer which is available for use.
 1181  * Select something from a free list.
 1182  * Preference is to AGE list, then LRU list.
 1183  *
 1184  * Called at splbio and with buffer queues locked.
 1185  * Return buffer locked.
 1186  */
 1187 struct buf *
 1188 getnewbuf(int slpflag, int slptimeo, int from_bufq)
 1189 {
 1190         struct buf *bp;
 1191 
 1192 start:
 1193         LOCK_ASSERT(simple_lock_held(&bqueue_slock));
 1194 
 1195         /*
 1196          * Get a new buffer from the pool; but use NOWAIT because
 1197          * we have the buffer queues locked.
 1198          */
 1199         if (!from_bufq && buf_lotsfree() &&
 1200             (bp = pool_get(&bufpool, PR_NOWAIT)) != NULL) {
 1201                 memset((char *)bp, 0, sizeof(*bp));
 1202                 BUF_INIT(bp);
 1203                 bp->b_dev = NODEV;
 1204                 bp->b_vnbufs.le_next = NOLIST;
 1205                 bp->b_flags = B_BUSY;
 1206                 simple_lock(&bp->b_interlock);
 1207 #if defined(DIAGNOSTIC)
 1208                 bp->b_freelistindex = -1;
 1209 #endif /* defined(DIAGNOSTIC) */
 1210                 return (bp);
 1211         }
 1212 
 1213         if ((bp = TAILQ_FIRST(&bufqueues[BQ_AGE].bq_queue)) != NULL ||
 1214             (bp = TAILQ_FIRST(&bufqueues[BQ_LRU].bq_queue)) != NULL) {
 1215                 simple_lock(&bp->b_interlock);
 1216                 bremfree(bp);
 1217         } else {
 1218                 /*
 1219                  * XXX: !from_bufq should be removed.
 1220                  */
 1221                 if (!from_bufq || curproc != uvm.pagedaemon_proc) {
 1222                         /* wait for a free buffer of any kind */
 1223                         needbuffer = 1;
 1224                         ltsleep(&needbuffer, slpflag|(PRIBIO + 1),
 1225                             "getnewbuf", slptimeo, &bqueue_slock);
 1226                 }
 1227                 return (NULL);
 1228         }
 1229 
 1230 #ifdef DIAGNOSTIC
 1231         if (bp->b_bufsize <= 0)
 1232                 panic("buffer %p: on queue but empty", bp);
 1233 #endif
 1234 
 1235         if (ISSET(bp->b_flags, B_VFLUSH)) {
 1236                 /*
 1237                  * This is a delayed write buffer being flushed to disk.  Make
 1238                  * sure it gets aged out of the queue when it's finished, and
 1239                  * leave it off the LRU queue.
 1240                  */
 1241                 CLR(bp->b_flags, B_VFLUSH);
 1242                 SET(bp->b_flags, B_AGE);
 1243                 simple_unlock(&bp->b_interlock);
 1244                 goto start;
 1245         }
 1246 
 1247         /* Buffer is no longer on free lists. */
 1248         SET(bp->b_flags, B_BUSY);
 1249 
 1250         /*
 1251          * If buffer was a delayed write, start it and return NULL
 1252          * (since we might sleep while starting the write).
 1253          */
 1254         if (ISSET(bp->b_flags, B_DELWRI)) {
 1255                 /*
 1256                  * This buffer has gone through the LRU, so make sure it gets
 1257                  * reused ASAP.
 1258                  */
 1259                 SET(bp->b_flags, B_AGE);
 1260                 simple_unlock(&bp->b_interlock);
 1261                 simple_unlock(&bqueue_slock);
 1262                 bawrite(bp);
 1263                 simple_lock(&bqueue_slock);
 1264                 return (NULL);
 1265         }
 1266 
 1267         /* disassociate us from our vnode, if we had one... */
 1268         if (bp->b_vp)
 1269                 brelvp(bp);
 1270 
 1271         if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_deallocate)
 1272                 (*bioops.io_deallocate)(bp);
 1273 
 1274         /* clear out various other fields */
 1275         bp->b_flags = B_BUSY;
 1276         bp->b_dev = NODEV;
 1277         bp->b_blkno = bp->b_lblkno = bp->b_rawblkno = 0;
 1278         bp->b_iodone = 0;
 1279         bp->b_error = 0;
 1280         bp->b_resid = 0;
 1281         bp->b_bcount = 0;
 1282 
 1283         bremhash(bp);
 1284         return (bp);
 1285 }
 1286 
 1287 /*
 1288  * Attempt to free an aged buffer off the queues.
 1289  * Called at splbio and with queue lock held.
 1290  * Returns the amount of buffer memory freed.
 1291  */
 1292 static int
 1293 buf_trim(void)
 1294 {
 1295         struct buf *bp;
 1296         long size = 0;
 1297 
 1298         /* Instruct getnewbuf() to get buffers off the queues */
 1299         if ((bp = getnewbuf(PCATCH, 1, 1)) == NULL)
 1300                 return 0;
 1301 
 1302         KASSERT(!ISSET(bp->b_flags, B_WANTED));
 1303         simple_unlock(&bp->b_interlock);
 1304         size = bp->b_bufsize;
 1305         bufmem -= size;
 1306         simple_unlock(&bqueue_slock);
 1307         if (size > 0) {
 1308                 buf_mrelease(bp->b_data, size);
 1309                 bp->b_bcount = bp->b_bufsize = 0;
 1310         }
 1311         /* brelse() will return the buffer to the global buffer pool */
 1312         brelse(bp);
 1313         simple_lock(&bqueue_slock);
 1314         return size;
 1315 }
 1316 
 1317 int
 1318 buf_drain(int n)
 1319 {
 1320         int s, size = 0, sz;
 1321 
 1322         s = splbio();
 1323         simple_lock(&bqueue_slock);
 1324 
 1325         while (size < n && bufmem > bufmem_lowater) {
 1326                 sz = buf_trim();
 1327                 if (sz <= 0)
 1328                         break;
 1329                 size += sz;
 1330         }
 1331 
 1332         simple_unlock(&bqueue_slock);
 1333         splx(s);
 1334         return size;
 1335 }
 1336 
 1337 /*
 1338  * Wait for operations on the buffer to complete.
 1339  * When they do, extract and return the I/O's error value.
 1340  */
 1341 int
 1342 biowait(struct buf *bp)
 1343 {
 1344         int s, error;
 1345 
 1346         s = splbio();
 1347         simple_lock(&bp->b_interlock);
 1348         while (!ISSET(bp->b_flags, B_DONE | B_DELWRI))
 1349                 ltsleep(bp, PRIBIO + 1, "biowait", 0, &bp->b_interlock);
 1350 
 1351         /* check for interruption of I/O (e.g. via NFS), then errors. */
 1352         if (ISSET(bp->b_flags, B_EINTR)) {
 1353                 CLR(bp->b_flags, B_EINTR);
 1354                 error = EINTR;
 1355         } else if (ISSET(bp->b_flags, B_ERROR))
 1356                 error = bp->b_error ? bp->b_error : EIO;
 1357         else
 1358                 error = 0;
 1359 
 1360         simple_unlock(&bp->b_interlock);
 1361         splx(s);
 1362         return (error);
 1363 }
 1364 
 1365 /*
 1366  * Mark I/O complete on a buffer.
 1367  *
 1368  * If a callback has been requested, e.g. the pageout
 1369  * daemon, do so. Otherwise, awaken waiting processes.
 1370  *
 1371  * [ Leffler, et al., says on p.247:
 1372  *      "This routine wakes up the blocked process, frees the buffer
 1373  *      for an asynchronous write, or, for a request by the pagedaemon
 1374  *      process, invokes a procedure specified in the buffer structure" ]
 1375  *
 1376  * In real life, the pagedaemon (or other system processes) wants
 1377  * to do async stuff to, and doesn't want the buffer brelse()'d.
 1378  * (for swap pager, that puts swap buffers on the free lists (!!!),
 1379  * for the vn device, that puts malloc'd buffers on the free lists!)
 1380  */
 1381 void
 1382 biodone(struct buf *bp)
 1383 {
 1384         int s = splbio();
 1385 
 1386         simple_lock(&bp->b_interlock);
 1387         if (ISSET(bp->b_flags, B_DONE))
 1388                 panic("biodone already");
 1389         SET(bp->b_flags, B_DONE);               /* note that it's done */
 1390         BIO_SETPRIO(bp, BPRIO_DEFAULT);
 1391 
 1392         if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_complete)
 1393                 (*bioops.io_complete)(bp);
 1394 
 1395         if (!ISSET(bp->b_flags, B_READ))        /* wake up reader */
 1396                 vwakeup(bp);
 1397 
 1398         /*
 1399          * If necessary, call out.  Unlock the buffer before calling
 1400          * iodone() as the buffer isn't valid any more when it return.
 1401          */
 1402         if (ISSET(bp->b_flags, B_CALL)) {
 1403                 CLR(bp->b_flags, B_CALL);       /* but note callout done */
 1404                 simple_unlock(&bp->b_interlock);
 1405                 (*bp->b_iodone)(bp);
 1406         } else {
 1407                 if (ISSET(bp->b_flags, B_ASYNC)) {      /* if async, release */
 1408                         simple_unlock(&bp->b_interlock);
 1409                         brelse(bp);
 1410                 } else {                        /* or just wakeup the buffer */
 1411                         CLR(bp->b_flags, B_WANTED);
 1412                         wakeup(bp);
 1413                         simple_unlock(&bp->b_interlock);
 1414                 }
 1415         }
 1416 
 1417         splx(s);
 1418 }
 1419 
 1420 /*
 1421  * Return a count of buffers on the "locked" queue.
 1422  */
 1423 int
 1424 count_lock_queue(void)
 1425 {
 1426         struct buf *bp;
 1427         int n = 0;
 1428 
 1429         simple_lock(&bqueue_slock);
 1430         TAILQ_FOREACH(bp, &bufqueues[BQ_LOCKED].bq_queue, b_freelist)
 1431                 n++;
 1432         simple_unlock(&bqueue_slock);
 1433         return (n);
 1434 }
 1435 
 1436 /*
 1437  * Wait for all buffers to complete I/O
 1438  * Return the number of "stuck" buffers.
 1439  */
 1440 int
 1441 buf_syncwait(void)
 1442 {
 1443         struct buf *bp;
 1444         int iter, nbusy, nbusy_prev = 0, dcount, s, ihash;
 1445 
 1446         dcount = 10000;
 1447         for (iter = 0; iter < 20;) {
 1448                 s = splbio();
 1449                 simple_lock(&bqueue_slock);
 1450                 nbusy = 0;
 1451                 for (ihash = 0; ihash < bufhash+1; ihash++) {
 1452                     LIST_FOREACH(bp, &bufhashtbl[ihash], b_hash) {
 1453                         if ((bp->b_flags & (B_BUSY|B_INVAL|B_READ)) == B_BUSY)
 1454                                 nbusy++;
 1455                         /*
 1456                          * With soft updates, some buffers that are
 1457                          * written will be remarked as dirty until other
 1458                          * buffers are written.
 1459                          */
 1460                         if (bp->b_vp && bp->b_vp->v_mount
 1461                             && (bp->b_vp->v_mount->mnt_flag & MNT_SOFTDEP)
 1462                             && (bp->b_flags & B_DELWRI)) {
 1463                                 simple_lock(&bp->b_interlock);
 1464                                 bremfree(bp);
 1465                                 bp->b_flags |= B_BUSY;
 1466                                 nbusy++;
 1467                                 simple_unlock(&bp->b_interlock);
 1468                                 simple_unlock(&bqueue_slock);
 1469                                 bawrite(bp);
 1470                                 if (dcount-- <= 0) {
 1471                                         printf("softdep ");
 1472                                         splx(s);
 1473                                         goto fail;
 1474                                 }
 1475                                 simple_lock(&bqueue_slock);
 1476                         }
 1477                     }
 1478                 }
 1479 
 1480                 simple_unlock(&bqueue_slock);
 1481                 splx(s);
 1482 
 1483                 if (nbusy == 0)
 1484                         break;
 1485                 if (nbusy_prev == 0)
 1486                         nbusy_prev = nbusy;
 1487                 printf("%d ", nbusy);
 1488                 tsleep(&nbusy, PRIBIO, "bflush",
 1489                     (iter == 0) ? 1 : hz / 25 * iter);
 1490                 if (nbusy >= nbusy_prev) /* we didn't flush anything */
 1491                         iter++;
 1492                 else
 1493                         nbusy_prev = nbusy;
 1494         }
 1495 
 1496         if (nbusy) {
 1497 fail:;
 1498 #if defined(DEBUG) || defined(DEBUG_HALT_BUSY)
 1499                 printf("giving up\nPrinting vnodes for busy buffers\n");
 1500                 s = splbio();
 1501                 for (ihash = 0; ihash < bufhash+1; ihash++) {
 1502                     LIST_FOREACH(bp, &bufhashtbl[ihash], b_hash) {
 1503                         if ((bp->b_flags & (B_BUSY|B_INVAL|B_READ)) == B_BUSY)
 1504                                 vprint(NULL, bp->b_vp);
 1505                     }
 1506                 }
 1507                 splx(s);
 1508 #endif
 1509         }
 1510 
 1511         return nbusy;
 1512 }
 1513 
 1514 static void
 1515 sysctl_fillbuf(struct buf *i, struct buf_sysctl *o)
 1516 {
 1517 
 1518         o->b_flags = i->b_flags;
 1519         o->b_error = i->b_error;
 1520         o->b_prio = i->b_prio;
 1521         o->b_dev = i->b_dev;
 1522         o->b_bufsize = i->b_bufsize;
 1523         o->b_bcount = i->b_bcount;
 1524         o->b_resid = i->b_resid;
 1525         o->b_addr = PTRTOUINT64(i->b_un.b_addr);
 1526         o->b_blkno = i->b_blkno;
 1527         o->b_rawblkno = i->b_rawblkno;
 1528         o->b_iodone = PTRTOUINT64(i->b_iodone);
 1529         o->b_proc = PTRTOUINT64(i->b_proc);
 1530         o->b_vp = PTRTOUINT64(i->b_vp);
 1531         o->b_saveaddr = PTRTOUINT64(i->b_saveaddr);
 1532         o->b_lblkno = i->b_lblkno;
 1533 }
 1534 
 1535 #define KERN_BUFSLOP 20
 1536 static int
 1537 sysctl_dobuf(SYSCTLFN_ARGS)
 1538 {
 1539         struct buf *bp;
 1540         struct buf_sysctl bs;
 1541         char *dp;
 1542         u_int i, op, arg;
 1543         size_t len, needed, elem_size, out_size;
 1544         int error, s, elem_count;
 1545 
 1546         if (namelen == 1 && name[0] == CTL_QUERY)
 1547                 return (sysctl_query(SYSCTLFN_CALL(rnode)));
 1548 
 1549         if (namelen != 4)
 1550                 return (EINVAL);
 1551 
 1552         dp = oldp;
 1553         len = (oldp != NULL) ? *oldlenp : 0;
 1554         op = name[0];
 1555         arg = name[1];
 1556         elem_size = name[2];
 1557         elem_count = name[3];
 1558         out_size = MIN(sizeof(bs), elem_size);
 1559 
 1560         /*
 1561          * at the moment, these are just "placeholders" to make the
 1562          * API for retrieving kern.buf data more extensible in the
 1563          * future.
 1564          *
 1565          * XXX kern.buf currently has "netbsd32" issues.  hopefully
 1566          * these will be resolved at a later point.
 1567          */
 1568         if (op != KERN_BUF_ALL || arg != KERN_BUF_ALL ||
 1569             elem_size < 1 || elem_count < 0)
 1570                 return (EINVAL);
 1571 
 1572         error = 0;
 1573         needed = 0;
 1574         s = splbio();
 1575         simple_lock(&bqueue_slock);
 1576         for (i = 0; i < BQUEUES; i++) {
 1577                 TAILQ_FOREACH(bp, &bufqueues[i].bq_queue, b_freelist) {
 1578                         if (len >= elem_size && elem_count > 0) {
 1579                                 sysctl_fillbuf(bp, &bs);
 1580                                 error = copyout(&bs, dp, out_size);
 1581                                 if (error)
 1582                                         goto cleanup;
 1583                                 dp += elem_size;
 1584                                 len -= elem_size;
 1585                         }
 1586                         if (elem_count > 0) {
 1587                                 needed += elem_size;
 1588                                 if (elem_count != INT_MAX)
 1589                                         elem_count--;
 1590                         }
 1591                 }
 1592         }
 1593 cleanup:
 1594         simple_unlock(&bqueue_slock);
 1595         splx(s);
 1596 
 1597         *oldlenp = needed;
 1598         if (oldp == NULL)
 1599                 *oldlenp += KERN_BUFSLOP * sizeof(struct buf);
 1600 
 1601         return (error);
 1602 }
 1603 
 1604 static int
 1605 sysctl_bufvm_update(SYSCTLFN_ARGS)
 1606 {
 1607         int t, error;
 1608         struct sysctlnode node;
 1609 
 1610         node = *rnode;
 1611         node.sysctl_data = &t;
 1612         t = *(int *)rnode->sysctl_data;
 1613         error = sysctl_lookup(SYSCTLFN_CALL(&node));
 1614         if (error || newp == NULL)
 1615                 return (error);
 1616 
 1617         if (t < 0)
 1618                 return EINVAL;
 1619         if (rnode->sysctl_data == &bufcache) {
 1620                 if (t > 100)
 1621                         return (EINVAL);
 1622                 bufcache = t;
 1623                 buf_setwm();
 1624         } else if (rnode->sysctl_data == &bufmem_lowater) {
 1625                 if (bufmem_hiwater - t < 16)
 1626                         return (EINVAL);
 1627                 bufmem_lowater = t;
 1628         } else if (rnode->sysctl_data == &bufmem_hiwater) {
 1629                 if (t - bufmem_lowater < 16)
 1630                         return (EINVAL);
 1631                 bufmem_hiwater = t;
 1632         } else
 1633                 return (EINVAL);
 1634 
 1635         /* Drain until below new high water mark */
 1636         while ((t = bufmem - bufmem_hiwater) >= 0) {
 1637                 if (buf_drain(t / (2 * 1024)) <= 0)
 1638                         break;
 1639         }
 1640 
 1641         return 0;
 1642 }
 1643 
 1644 SYSCTL_SETUP(sysctl_kern_buf_setup, "sysctl kern.buf subtree setup")
 1645 {
 1646 
 1647         sysctl_createv(clog, 0, NULL, NULL,
 1648                        CTLFLAG_PERMANENT,
 1649                        CTLTYPE_NODE, "kern", NULL,
 1650                        NULL, 0, NULL, 0,
 1651                        CTL_KERN, CTL_EOL);
 1652         sysctl_createv(clog, 0, NULL, NULL,
 1653                        CTLFLAG_PERMANENT,
 1654                        CTLTYPE_NODE, "buf",
 1655                        SYSCTL_DESCR("Kernel buffer cache information"),
 1656                        sysctl_dobuf, 0, NULL, 0,
 1657                        CTL_KERN, KERN_BUF, CTL_EOL);
 1658 }
 1659 
 1660 SYSCTL_SETUP(sysctl_vm_buf_setup, "sysctl vm.buf* subtree setup")
 1661 {
 1662 
 1663         sysctl_createv(clog, 0, NULL, NULL,
 1664                        CTLFLAG_PERMANENT,
 1665                        CTLTYPE_NODE, "vm", NULL,
 1666                        NULL, 0, NULL, 0,
 1667                        CTL_VM, CTL_EOL);
 1668 
 1669         sysctl_createv(clog, 0, NULL, NULL,
 1670                        CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
 1671                        CTLTYPE_INT, "bufcache",
 1672                        SYSCTL_DESCR("Percentage of physical memory to use for "
 1673                                     "buffer cache"),
 1674                        sysctl_bufvm_update, 0, &bufcache, 0,
 1675                        CTL_VM, CTL_CREATE, CTL_EOL);
 1676         sysctl_createv(clog, 0, NULL, NULL,
 1677                        CTLFLAG_PERMANENT|CTLFLAG_READONLY,
 1678                        CTLTYPE_INT, "bufmem",
 1679                        SYSCTL_DESCR("Amount of kernel memory used by buffer "
 1680                                     "cache"),
 1681                        NULL, 0, &bufmem, 0,
 1682                        CTL_VM, CTL_CREATE, CTL_EOL);
 1683         sysctl_createv(clog, 0, NULL, NULL,
 1684                        CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
 1685                        CTLTYPE_INT, "bufmem_lowater",
 1686                        SYSCTL_DESCR("Minimum amount of kernel memory to "
 1687                                     "reserve for buffer cache"),
 1688                        sysctl_bufvm_update, 0, &bufmem_lowater, 0,
 1689                        CTL_VM, CTL_CREATE, CTL_EOL);
 1690         sysctl_createv(clog, 0, NULL, NULL,
 1691                        CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
 1692                        CTLTYPE_INT, "bufmem_hiwater",
 1693                        SYSCTL_DESCR("Maximum amount of kernel memory to use "
 1694                                     "for buffer cache"),
 1695                        sysctl_bufvm_update, 0, &bufmem_hiwater, 0,
 1696                        CTL_VM, CTL_CREATE, CTL_EOL);
 1697 }
 1698 
 1699 #ifdef DEBUG
 1700 /*
 1701  * Print out statistics on the current allocation of the buffer pool.
 1702  * Can be enabled to print out on every ``sync'' by setting "syncprt"
 1703  * in vfs_syscalls.c using sysctl.
 1704  */
 1705 void
 1706 vfs_bufstats(void)
 1707 {
 1708         int s, i, j, count;
 1709         struct buf *bp;
 1710         struct bqueue *dp;
 1711         int counts[(MAXBSIZE / PAGE_SIZE) + 1];
 1712         static char *bname[BQUEUES] = { "LOCKED", "LRU", "AGE" };
 1713 
 1714         for (dp = bufqueues, i = 0; dp < &bufqueues[BQUEUES]; dp++, i++) {
 1715                 count = 0;
 1716                 for (j = 0; j <= MAXBSIZE/PAGE_SIZE; j++)
 1717                         counts[j] = 0;
 1718                 s = splbio();
 1719                 TAILQ_FOREACH(bp, &dp->bq_queue, b_freelist) {
 1720                         counts[bp->b_bufsize/PAGE_SIZE]++;
 1721                         count++;
 1722                 }
 1723                 splx(s);
 1724                 printf("%s: total-%d", bname[i], count);
 1725                 for (j = 0; j <= MAXBSIZE/PAGE_SIZE; j++)
 1726                         if (counts[j] != 0)
 1727                                 printf(", %d-%d", j * PAGE_SIZE, counts[j]);
 1728                 printf("\n");
 1729         }
 1730 }
 1731 #endif /* DEBUG */

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