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

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    1 /*      $NetBSD: kern_physio.c,v 1.60 2004/03/23 13:22:33 junyoung Exp $        */
    2 
    3 /*-
    4  * Copyright (c) 1982, 1986, 1990, 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  *      @(#)kern_physio.c       8.1 (Berkeley) 6/10/93
   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  *      @(#)kern_physio.c       8.1 (Berkeley) 6/10/93
   71  */
   72 
   73 #include <sys/cdefs.h>
   74 __KERNEL_RCSID(0, "$NetBSD: kern_physio.c,v 1.60 2004/03/23 13:22:33 junyoung Exp $");
   75 
   76 #include <sys/param.h>
   77 #include <sys/systm.h>
   78 #include <sys/buf.h>
   79 #include <sys/malloc.h>
   80 #include <sys/proc.h>
   81 
   82 #include <uvm/uvm_extern.h>
   83 
   84 /*
   85  * The routines implemented in this file are described in:
   86  *      Leffler, et al.: The Design and Implementation of the 4.3BSD
   87  *          UNIX Operating System (Addison Welley, 1989)
   88  * on pages 231-233.
   89  *
   90  * The routines "getphysbuf" and "putphysbuf" steal and return a swap
   91  * buffer.  Leffler, et al., says that swap buffers are used to do the
   92  * I/O, so raw I/O requests don't have to be single-threaded.
   93  */
   94 
   95 struct buf *getphysbuf(void);
   96 void putphysbuf(struct buf *bp);
   97 
   98 /*
   99  * Do "physical I/O" on behalf of a user.  "Physical I/O" is I/O directly
  100  * from the raw device to user buffers, and bypasses the buffer cache.
  101  *
  102  * Comments in brackets are from Leffler, et al.'s pseudo-code implementation.
  103  */
  104 int
  105 physio(strategy, bp, dev, flags, min_phys, uio)
  106         void (*strategy)(struct buf *);
  107         struct buf *bp;
  108         dev_t dev;
  109         int flags;
  110         void (*min_phys)(struct buf *);
  111         struct uio *uio;
  112 {
  113         struct iovec *iovp;
  114         struct lwp *l = curlwp;
  115         struct proc *p = l->l_proc;
  116         int error, done, i, nobuf, s;
  117         long todo;
  118 
  119         error = 0;
  120         flags &= B_READ | B_WRITE;
  121 
  122         /* Make sure we have a buffer, creating one if necessary. */
  123         if ((nobuf = (bp == NULL)) != 0) {
  124 
  125                 bp = getphysbuf();
  126                 /* bp was just malloc'd so can't already be busy */
  127                 bp->b_flags |= B_BUSY;
  128 
  129         } else {
  130 
  131                 /* [raise the processor priority level to splbio;] */
  132                 s = splbio();
  133 
  134                 /* [while the buffer is marked busy] */
  135                 while (bp->b_flags & B_BUSY) {
  136                         /* [mark the buffer wanted] */
  137                         bp->b_flags |= B_WANTED;
  138                         /* [wait until the buffer is available] */
  139                         tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0);
  140                 }
  141 
  142                 /* Mark it busy, so nobody else will use it. */
  143                 bp->b_flags |= B_BUSY;
  144 
  145                 /* [lower the priority level] */
  146                 splx(s);
  147         }
  148 
  149         /* [set up the fixed part of the buffer for a transfer] */
  150         bp->b_dev = dev;
  151         bp->b_error = 0;
  152         bp->b_proc = p;
  153         LIST_INIT(&bp->b_dep);
  154 
  155         /*
  156          * [while there are data to transfer and no I/O error]
  157          * Note that I/O errors are handled with a 'goto' at the bottom
  158          * of the 'while' loop.
  159          */
  160         for (i = 0; i < uio->uio_iovcnt; i++) {
  161                 iovp = &uio->uio_iov[i];
  162                 while (iovp->iov_len > 0) {
  163 
  164                         /*
  165                          * [mark the buffer busy for physical I/O]
  166                          * (i.e. set B_PHYS (because it's an I/O to user
  167                          * memory, and B_RAW, because B_RAW is to be
  168                          * "Set by physio for raw transfers.", in addition
  169                          * to the "busy" and read/write flag.)
  170                          */
  171                         bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags;
  172 
  173                         /* [set up the buffer for a maximum-sized transfer] */
  174                         bp->b_blkno = btodb(uio->uio_offset);
  175                         bp->b_bcount = iovp->iov_len;
  176                         bp->b_data = iovp->iov_base;
  177 
  178                         /*
  179                          * [call minphys to bound the transfer size]
  180                          * and remember the amount of data to transfer,
  181                          * for later comparison.
  182                          */
  183                         (*min_phys)(bp);
  184                         todo = bp->b_bcount;
  185 #ifdef DIAGNOSTIC
  186                         if (todo <= 0)
  187                                 panic("todo(%ld) <= 0; minphys broken", todo);
  188                         if (todo > MAXPHYS)
  189                                 panic("todo(%ld) > MAXPHYS; minphys broken",
  190                                       todo);
  191 #endif
  192 
  193                         /*
  194                          * [lock the part of the user address space involved
  195                          *    in the transfer]
  196                          * Beware vmapbuf(); it clobbers b_data and
  197                          * saves it in b_saveaddr.  However, vunmapbuf()
  198                          * restores it.
  199                          */
  200                         PHOLD(l);
  201                         error = uvm_vslock(p, bp->b_data, todo,
  202                                            (flags & B_READ) ?
  203                                            VM_PROT_WRITE : VM_PROT_READ);
  204                         if (error) {
  205                                 bp->b_flags |= B_ERROR;
  206                                 bp->b_error = error;
  207                                 goto after_vsunlock;
  208                         }
  209                         vmapbuf(bp, todo);
  210 
  211                         BIO_SETPRIO(bp, BPRIO_TIMECRITICAL);
  212 
  213                         /* [call strategy to start the transfer] */
  214                         (*strategy)(bp);
  215 
  216                         /*
  217                          * Note that the raise/wait/lower/get error
  218                          * steps below would be done by biowait(), but
  219                          * we want to unlock the address space before
  220                          * we lower the priority.
  221                          *
  222                          * [raise the priority level to splbio]
  223                          */
  224                         s = splbio();
  225 
  226                         /* [wait for the transfer to complete] */
  227                         while ((bp->b_flags & B_DONE) == 0)
  228                                 tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0);
  229 
  230                         /* Mark it busy again, so nobody else will use it. */
  231                         bp->b_flags |= B_BUSY;
  232 
  233                         /* [lower the priority level] */
  234                         splx(s);
  235 
  236                         /*
  237                          * [unlock the part of the address space previously
  238                          *    locked]
  239                          */
  240                         vunmapbuf(bp, todo);
  241                         uvm_vsunlock(p, bp->b_data, todo);
  242  after_vsunlock:
  243                         PRELE(l);
  244 
  245                         /* remember error value (save a splbio/splx pair) */
  246                         if (bp->b_flags & B_ERROR)
  247                                 error = (bp->b_error ? bp->b_error : EIO);
  248 
  249                         /*
  250                          * [deduct the transfer size from the total number
  251                          *    of data to transfer]
  252                          */
  253                         done = bp->b_bcount - bp->b_resid;
  254                         KASSERT(done >= 0);
  255                         KASSERT(done <= todo);
  256 
  257                         iovp->iov_len -= done;
  258                         iovp->iov_base = (caddr_t)iovp->iov_base + done;
  259                         uio->uio_offset += done;
  260                         uio->uio_resid -= done;
  261 
  262                         /*
  263                          * Now, check for an error.
  264                          * Also, handle weird end-of-disk semantics.
  265                          */
  266                         if (error || done < todo)
  267                                 goto done;
  268                 }
  269         }
  270 
  271 done:
  272         /*
  273          * [clean up the state of the buffer]
  274          * Remember if somebody wants it, so we can wake them up below.
  275          * Also, if we had to steal it, give it back.
  276          */
  277         s = splbio();
  278         bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW);
  279         if (nobuf)
  280                 putphysbuf(bp);
  281         else {
  282                 /*
  283                  * [if another process is waiting for the raw I/O buffer,
  284                  *    wake up processes waiting to do physical I/O;
  285                  */
  286                 if (bp->b_flags & B_WANTED) {
  287                         bp->b_flags &= ~B_WANTED;
  288                         wakeup(bp);
  289                 }
  290         }
  291         splx(s);
  292 
  293         return (error);
  294 }
  295 
  296 /*
  297  * allocate a buffer structure for use in physical I/O.
  298  */
  299 struct buf *
  300 getphysbuf()
  301 {
  302         struct buf *bp;
  303         int s;
  304 
  305         s = splbio();
  306         bp = pool_get(&bufpool, PR_WAITOK);
  307         splx(s);
  308         memset(bp, 0, sizeof(*bp));
  309         BUF_INIT(bp);
  310         return(bp);
  311 }
  312 
  313 /*
  314  * get rid of a swap buffer structure which has been used in physical I/O.
  315  */
  316 void
  317 putphysbuf(bp)
  318         struct buf *bp;
  319 {
  320         int s;
  321 
  322         if (__predict_false(bp->b_flags & B_WANTED))
  323                 panic("putphysbuf: private buf B_WANTED");
  324         s = splbio();
  325         pool_put(&bufpool, bp);
  326         splx(s);
  327 }
  328 
  329 /*
  330  * Leffler, et al., says on p. 231:
  331  * "The minphys() routine is called by physio() to adjust the
  332  * size of each I/O transfer before the latter is passed to
  333  * the strategy routine..."
  334  *
  335  * so, just adjust the buffer's count accounting to MAXPHYS here,
  336  * and return the new count;
  337  */
  338 void
  339 minphys(bp)
  340         struct buf *bp;
  341 {
  342 
  343         if (bp->b_bcount > MAXPHYS)
  344                 bp->b_bcount = MAXPHYS;
  345 }

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