FreeBSD/Linux Kernel Cross Reference
sys/sys/buf.h

     /*-
      * Copyright (c) 1982, 1986, 1989, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
      * the permission of UNIX System Laboratories, Inc.
      *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)buf.h       8.9 (Berkeley) 3/30/95
     * $FreeBSD: releng/10.3/sys/sys/buf.h 285402 2015-07-11 19:11:40Z kib $
     */
    
    #ifndef _SYS_BUF_H_
    #define _SYS_BUF_H_
    
    #include <sys/bufobj.h>
    #include <sys/queue.h>
    #include <sys/lock.h>
    #include <sys/lockmgr.h>
    
    struct bio;
    struct buf;
    struct bufobj;
    struct mount;
    struct vnode;
    struct uio;
    
    /*
     * To avoid including <ufs/ffs/softdep.h> 
     */   
    LIST_HEAD(workhead, worklist);
    /*
     * These are currently used only by the soft dependency code, hence
     * are stored once in a global variable. If other subsystems wanted
     * to use these hooks, a pointer to a set of bio_ops could be added
     * to each buffer.
     */
    extern struct bio_ops {
            void    (*io_start)(struct buf *);
            void    (*io_complete)(struct buf *);
            void    (*io_deallocate)(struct buf *);
            int     (*io_countdeps)(struct buf *, int);
    } bioops;
    
    struct vm_object;
    
    typedef unsigned char b_xflags_t;
    
    /*
     * The buffer header describes an I/O operation in the kernel.
     *
     * NOTES:
     *      b_bufsize, b_bcount.  b_bufsize is the allocation size of the
     *      buffer, either DEV_BSIZE or PAGE_SIZE aligned.  b_bcount is the
     *      originally requested buffer size and can serve as a bounds check
     *      against EOF.  For most, but not all uses, b_bcount == b_bufsize.
     *
     *      b_dirtyoff, b_dirtyend.  Buffers support piecemeal, unaligned
     *      ranges of dirty data that need to be written to backing store.
     *      The range is typically clipped at b_bcount ( not b_bufsize ).
     *
     *      b_resid.  Number of bytes remaining in I/O.  After an I/O operation
     *      completes, b_resid is usually 0 indicating 100% success.
     *
     *      All fields are protected by the buffer lock except those marked:
     *              V - Protected by owning bufobj lock
     *              Q - Protected by the buf queue lock
     *              D - Protected by an dependency implementation specific lock
     */
    struct buf {
            struct bufobj   *b_bufobj;
            long            b_bcount;
            void            *b_caller1;
            caddr_t         b_data;
           int             b_error;
           uint8_t         b_iocmd;
           uint8_t         b_ioflags;
           off_t           b_iooffset;
           long            b_resid;
           void    (*b_iodone)(struct buf *);
           daddr_t b_blkno;                /* Underlying physical block number. */
           off_t   b_offset;               /* Offset into file. */
           TAILQ_ENTRY(buf) b_bobufs;      /* (V) Buffer's associated vnode. */
           uint32_t        b_vflags;       /* (V) BV_* flags */
           TAILQ_ENTRY(buf) b_freelist;    /* (Q) Free list position inactive. */
           unsigned short b_qindex;        /* (Q) buffer queue index */
           uint32_t        b_flags;        /* B_* flags. */
           b_xflags_t b_xflags;            /* extra flags */
           struct lock b_lock;             /* Buffer lock */
           long    b_bufsize;              /* Allocated buffer size. */
           long    b_runningbufspace;      /* when I/O is running, pipelining */
           caddr_t b_kvabase;              /* base kva for buffer */
           caddr_t b_kvaalloc;             /* allocated kva for B_KVAALLOC */
           int     b_kvasize;              /* size of kva for buffer */
           daddr_t b_lblkno;               /* Logical block number. */
           struct  vnode *b_vp;            /* Device vnode. */
           int     b_dirtyoff;             /* Offset in buffer of dirty region. */
           int     b_dirtyend;             /* Offset of end of dirty region. */
           struct  ucred *b_rcred;         /* Read credentials reference. */
           struct  ucred *b_wcred;         /* Write credentials reference. */
           void    *b_saveaddr;            /* Original b_addr for physio. */
           union   pager_info {
                   int     pg_reqpage;
           } b_pager;
           union   cluster_info {
                   TAILQ_HEAD(cluster_list_head, buf) cluster_head;
                   TAILQ_ENTRY(buf) cluster_entry;
           } b_cluster;
           struct  vm_page *b_pages[btoc(MAXPHYS)];
           int             b_npages;
           struct  workhead b_dep;         /* (D) List of filesystem dependencies. */
           void    *b_fsprivate1;
           void    *b_fsprivate2;
           void    *b_fsprivate3;
           int     b_pin_count;
   };
   
   #define b_object        b_bufobj->bo_object
   
   /*
    * These flags are kept in b_flags.
    *
    * Notes:
    *
    *      B_ASYNC         VOP calls on bp's are usually async whether or not
    *                      B_ASYNC is set, but some subsystems, such as NFS, like 
    *                      to know what is best for the caller so they can
    *                      optimize the I/O.
    *
    *      B_PAGING        Indicates that bp is being used by the paging system or
    *                      some paging system and that the bp is not linked into
    *                      the b_vp's clean/dirty linked lists or ref counts.
    *                      Buffer vp reassignments are illegal in this case.
    *
    *      B_CACHE         This may only be set if the buffer is entirely valid.
    *                      The situation where B_DELWRI is set and B_CACHE is
    *                      clear MUST be committed to disk by getblk() so 
    *                      B_DELWRI can also be cleared.  See the comments for
    *                      getblk() in kern/vfs_bio.c.  If B_CACHE is clear,
    *                      the caller is expected to clear BIO_ERROR and B_INVAL,
    *                      set BIO_READ, and initiate an I/O.
    *
    *                      The 'entire buffer' is defined to be the range from
    *                      0 through b_bcount.
    *
    *      B_MALLOC        Request that the buffer be allocated from the malloc
    *                      pool, DEV_BSIZE aligned instead of PAGE_SIZE aligned.
    *
    *      B_CLUSTEROK     This flag is typically set for B_DELWRI buffers
    *                      by filesystems that allow clustering when the buffer
    *                      is fully dirty and indicates that it may be clustered
    *                      with other adjacent dirty buffers.  Note the clustering
    *                      may not be used with the stage 1 data write under NFS
    *                      but may be used for the commit rpc portion.
    *
    *      B_VMIO          Indicates that the buffer is tied into an VM object.
    *                      The buffer's data is always PAGE_SIZE aligned even
    *                      if b_bufsize and b_bcount are not.  ( b_bufsize is 
    *                      always at least DEV_BSIZE aligned, though ).
    *
    *      B_DIRECT        Hint that we should attempt to completely free
    *                      the pages underlying the buffer.  B_DIRECT is
    *                      sticky until the buffer is released and typically
    *                      only has an effect when B_RELBUF is also set.
    *
    */
   
   #define B_AGE           0x00000001      /* Move to age queue when I/O done. */
   #define B_NEEDCOMMIT    0x00000002      /* Append-write in progress. */
   #define B_ASYNC         0x00000004      /* Start I/O, do not wait. */
   #define B_DIRECT        0x00000008      /* direct I/O flag (pls free vmio) */
   #define B_DEFERRED      0x00000010      /* Skipped over for cleaning */
   #define B_CACHE         0x00000020      /* Bread found us in the cache. */
   #define B_VALIDSUSPWRT  0x00000040      /* Valid write during suspension. */
   #define B_DELWRI        0x00000080      /* Delay I/O until buffer reused. */
   #define B_PERSISTENT    0x00000100      /* Perm. ref'ed while EXT2FS mounted. */
   #define B_DONE          0x00000200      /* I/O completed. */
   #define B_EINTR         0x00000400      /* I/O was interrupted */
   #define B_UNMAPPED      0x00000800      /* KVA is not mapped. */
   #define B_KVAALLOC      0x00001000      /* But allocated. */
   #define B_INVAL         0x00002000      /* Does not contain valid info. */
   #define B_BARRIER       0x00004000      /* Write this and all preceeding first. */
   #define B_NOCACHE       0x00008000      /* Do not cache block after use. */
   #define B_MALLOC        0x00010000      /* malloced b_data */
   #define B_CLUSTEROK     0x00020000      /* Pagein op, so swap() can count it. */
   #define B_000400000     0x00040000      /* Available flag. */
   #define B_000800000     0x00080000      /* Available flag. */
   #define B_00100000      0x00100000      /* Available flag. */
   #define B_DIRTY         0x00200000      /* Needs writing later (in EXT2FS). */
   #define B_RELBUF        0x00400000      /* Release VMIO buffer. */
   #define B_00800000      0x00800000      /* Available flag. */
   #define B_NOCOPY        0x01000000      /* Don't copy-on-write this buf. */
   #define B_INFREECNT     0x02000000      /* buf is counted in numfreebufs */
   #define B_PAGING        0x04000000      /* volatile paging I/O -- bypass VMIO */
   #define B_MANAGED       0x08000000      /* Managed by FS. */
   #define B_RAM           0x10000000      /* Read ahead mark (flag) */
   #define B_VMIO          0x20000000      /* VMIO flag */
   #define B_CLUSTER       0x40000000      /* pagein op, so swap() can count it */
   #define B_REMFREE       0x80000000      /* Delayed bremfree */
   
   #define PRINT_BUF_FLAGS "\2\40remfree\37cluster\36vmio\35ram\34managed" \
           "\33paging\32infreecnt\31nocopy\30b23\27relbuf\26dirty\25b20" \
           "\24b19\23b18\22clusterok\21malloc\20nocache\17b14\16inval" \
           "\15kvaalloc\14unmapped\13eintr\12done\11persist\10delwri" \
           "\7validsuspwrt\6cache\5deferred\4direct\3async\2needcommit\1age"
   
   /*
    * These flags are kept in b_xflags.
    */
   #define BX_VNDIRTY      0x00000001      /* On vnode dirty list */
   #define BX_VNCLEAN      0x00000002      /* On vnode clean list */
   #define BX_BKGRDWRITE   0x00000010      /* Do writes in background */
   #define BX_BKGRDMARKER  0x00000020      /* Mark buffer for splay tree */
   #define BX_ALTDATA      0x00000040      /* Holds extended data */
   
   #define PRINT_BUF_XFLAGS "\2\7altdata\6bkgrdmarker\5bkgrdwrite\2clean\1dirty"
   
   #define NOOFFSET        (-1LL)          /* No buffer offset calculated yet */
   
   /*
    * These flags are kept in b_vflags.
    */
   #define BV_SCANNED      0x00000001      /* VOP_FSYNC funcs mark written bufs */
   #define BV_BKGRDINPROG  0x00000002      /* Background write in progress */
   #define BV_BKGRDWAIT    0x00000004      /* Background write waiting */
   #define BV_BKGRDERR     0x00000008      /* Error from background write */
   
   #define PRINT_BUF_VFLAGS "\2\4bkgrderr\3bkgrdwait\2bkgrdinprog\1scanned"
   
   #ifdef _KERNEL
   /*
    * Buffer locking
    */
   extern const char *buf_wmesg;           /* Default buffer lock message */
   #define BUF_WMESG "bufwait"
   #include <sys/proc.h>                   /* XXX for curthread */
   #include <sys/mutex.h>
   
   /*
    * Initialize a lock.
    */
   #define BUF_LOCKINIT(bp)                                                \
           lockinit(&(bp)->b_lock, PRIBIO + 4, buf_wmesg, 0, 0)
   /*
    *
    * Get a lock sleeping non-interruptably until it becomes available.
    */
   #define BUF_LOCK(bp, locktype, interlock)                               \
           _lockmgr_args_rw(&(bp)->b_lock, (locktype), (interlock),        \
               LK_WMESG_DEFAULT, LK_PRIO_DEFAULT, LK_TIMO_DEFAULT,         \
               LOCK_FILE, LOCK_LINE)
   
   /*
    * Get a lock sleeping with specified interruptably and timeout.
    */
   #define BUF_TIMELOCK(bp, locktype, interlock, wmesg, catch, timo)       \
           _lockmgr_args_rw(&(bp)->b_lock, (locktype) | LK_TIMELOCK,       \
               (interlock), (wmesg), (PRIBIO + 4) | (catch), (timo),       \
               LOCK_FILE, LOCK_LINE)
   
   /*
    * Release a lock. Only the acquiring process may free the lock unless
    * it has been handed off to biodone.
    */
   #define BUF_UNLOCK(bp) do {                                             \
           KASSERT(((bp)->b_flags & B_REMFREE) == 0,                       \
               ("BUF_UNLOCK %p while B_REMFREE is still set.", (bp)));     \
                                                                           \
           (void)_lockmgr_args(&(bp)->b_lock, LK_RELEASE, NULL,            \
               LK_WMESG_DEFAULT, LK_PRIO_DEFAULT, LK_TIMO_DEFAULT,         \
               LOCK_FILE, LOCK_LINE);                                      \
   } while (0)
   
   /*
    * Check if a buffer lock is recursed.
    */
   #define BUF_LOCKRECURSED(bp)                                            \
           lockmgr_recursed(&(bp)->b_lock)
   
   /*
    * Check if a buffer lock is currently held.
    */
   #define BUF_ISLOCKED(bp)                                                \
           lockstatus(&(bp)->b_lock)
   /*
    * Free a buffer lock.
    */
   #define BUF_LOCKFREE(bp)                                                \
           lockdestroy(&(bp)->b_lock)
   
   /*
    * Print informations on a buffer lock.
    */
   #define BUF_LOCKPRINTINFO(bp)                                           \
           lockmgr_printinfo(&(bp)->b_lock)
   
   /*
    * Buffer lock assertions.
    */
   #if defined(INVARIANTS) && defined(INVARIANT_SUPPORT)
   #define BUF_ASSERT_LOCKED(bp)                                           \
           _lockmgr_assert(&(bp)->b_lock, KA_LOCKED, LOCK_FILE, LOCK_LINE)
   #define BUF_ASSERT_SLOCKED(bp)                                          \
           _lockmgr_assert(&(bp)->b_lock, KA_SLOCKED, LOCK_FILE, LOCK_LINE)
   #define BUF_ASSERT_XLOCKED(bp)                                          \
           _lockmgr_assert(&(bp)->b_lock, KA_XLOCKED, LOCK_FILE, LOCK_LINE)
   #define BUF_ASSERT_UNLOCKED(bp)                                         \
           _lockmgr_assert(&(bp)->b_lock, KA_UNLOCKED, LOCK_FILE, LOCK_LINE)
   #define BUF_ASSERT_HELD(bp)
   #define BUF_ASSERT_UNHELD(bp)
   #else
   #define BUF_ASSERT_LOCKED(bp)
   #define BUF_ASSERT_SLOCKED(bp)
   #define BUF_ASSERT_XLOCKED(bp)
   #define BUF_ASSERT_UNLOCKED(bp)
   #define BUF_ASSERT_HELD(bp)
   #define BUF_ASSERT_UNHELD(bp)
   #endif
   
   #ifdef _SYS_PROC_H_     /* Avoid #include <sys/proc.h> pollution */
   /*
    * When initiating asynchronous I/O, change ownership of the lock to the
    * kernel. Once done, the lock may legally released by biodone. The
    * original owning process can no longer acquire it recursively, but must
    * wait until the I/O is completed and the lock has been freed by biodone.
    */
   #define BUF_KERNPROC(bp)                                                \
           _lockmgr_disown(&(bp)->b_lock, LOCK_FILE, LOCK_LINE)
   #endif
   
   /*
    * Find out if the lock has waiters or not.
    */
   #define BUF_LOCKWAITERS(bp)                                             \
           lockmgr_waiters(&(bp)->b_lock)
   
   #endif /* _KERNEL */
   
   struct buf_queue_head {
           TAILQ_HEAD(buf_queue, buf) queue;
           daddr_t last_pblkno;
           struct  buf *insert_point;
           struct  buf *switch_point;
   };
   
   /*
    * This structure describes a clustered I/O.  It is stored in the b_saveaddr
    * field of the buffer on which I/O is done.  At I/O completion, cluster
    * callback uses the structure to parcel I/O's to individual buffers, and
    * then free's this structure.
    */
   struct cluster_save {
           long    bs_bcount;              /* Saved b_bcount. */
           long    bs_bufsize;             /* Saved b_bufsize. */
           void    *bs_saveaddr;           /* Saved b_addr. */
           int     bs_nchildren;           /* Number of associated buffers. */
           struct buf **bs_children;       /* List of associated buffers. */
   };
   
   #ifdef _KERNEL
   
   static __inline int
   bwrite(struct buf *bp)
   {
   
           KASSERT(bp->b_bufobj != NULL, ("bwrite: no bufobj bp=%p", bp));
           KASSERT(bp->b_bufobj->bo_ops != NULL, ("bwrite: no bo_ops bp=%p", bp));
           KASSERT(bp->b_bufobj->bo_ops->bop_write != NULL,
               ("bwrite: no bop_write bp=%p", bp));
           return (BO_WRITE(bp->b_bufobj, bp));
   }
   
   static __inline void
   bstrategy(struct buf *bp)
   {
   
           KASSERT(bp->b_bufobj != NULL, ("bstrategy: no bufobj bp=%p", bp));
           KASSERT(bp->b_bufobj->bo_ops != NULL,
               ("bstrategy: no bo_ops bp=%p", bp));
           KASSERT(bp->b_bufobj->bo_ops->bop_strategy != NULL,
               ("bstrategy: no bop_strategy bp=%p", bp));
           BO_STRATEGY(bp->b_bufobj, bp);
   }
   
   static __inline void
   buf_start(struct buf *bp)
   {
           if (bioops.io_start)
                   (*bioops.io_start)(bp);
   }
   
   static __inline void
   buf_complete(struct buf *bp)
   {
           if (bioops.io_complete)
                   (*bioops.io_complete)(bp);
   }
   
   static __inline void
   buf_deallocate(struct buf *bp)
   {
           if (bioops.io_deallocate)
                   (*bioops.io_deallocate)(bp);
   }
   
   static __inline int
   buf_countdeps(struct buf *bp, int i)
   {
           if (bioops.io_countdeps)
                   return ((*bioops.io_countdeps)(bp, i));
           else
                   return (0);
   }
   
   #endif /* _KERNEL */
   
   /*
    * Zero out the buffer's data area.
    */
   #define clrbuf(bp) {                                                    \
           bzero((bp)->b_data, (u_int)(bp)->b_bcount);                     \
           (bp)->b_resid = 0;                                              \
   }
   
   /*
    * Flags for getblk's last parameter.
    */
   #define GB_LOCK_NOWAIT  0x0001          /* Fail if we block on a buf lock. */
   #define GB_NOCREAT      0x0002          /* Don't create a buf if not found. */
   #define GB_NOWAIT_BD    0x0004          /* Do not wait for bufdaemon. */
   #define GB_UNMAPPED     0x0008          /* Do not mmap buffer pages. */
   #define GB_KVAALLOC     0x0010          /* But allocate KVA. */
   
   #ifdef _KERNEL
   extern int      nbuf;                   /* The number of buffer headers */
   extern long     maxswzone;              /* Max KVA for swap structures */
   extern long     maxbcache;              /* Max KVA for buffer cache */
   extern long     runningbufspace;
   extern long     hibufspace;
   extern int      dirtybufthresh;
   extern int      bdwriteskip;
   extern int      dirtybufferflushes;
   extern int      altbufferflushes;
   extern struct   buf *buf;               /* The buffer headers. */
   extern struct   buf *swbuf;             /* Swap I/O buffer headers. */
   extern int      nswbuf;                 /* Number of swap I/O buffer headers. */
   extern int      cluster_pbuf_freecnt;   /* Number of pbufs for clusters */
   extern int      vnode_pbuf_freecnt;     /* Number of pbufs for vnode pager */
   extern caddr_t  unmapped_buf;
   
   void    runningbufwakeup(struct buf *);
   void    waitrunningbufspace(void);
   caddr_t kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est);
   void    bufinit(void);
   void    bdata2bio(struct buf *bp, struct bio *bip);
   void    bwillwrite(void);
   int     buf_dirty_count_severe(void);
   void    bremfree(struct buf *);
   void    bremfreef(struct buf *);        /* XXX Force bremfree, only for nfs. */
   #define bread(vp, blkno, size, cred, bpp) \
               breadn_flags(vp, blkno, size, NULL, NULL, 0, cred, 0, bpp)
   #define bread_gb(vp, blkno, size, cred, gbflags, bpp) \
               breadn_flags(vp, blkno, size, NULL, NULL, 0, cred, \
                   gbflags, bpp)
   #define breadn(vp, blkno, size, rablkno, rabsize, cnt, cred, bpp) \
               breadn_flags(vp, blkno, size, rablkno, rabsize, cnt, cred, 0, bpp)
   int     breadn_flags(struct vnode *, daddr_t, int, daddr_t *, int *, int,
               struct ucred *, int, struct buf **);
   void    breada(struct vnode *, daddr_t *, int *, int, struct ucred *);
   void    bdwrite(struct buf *);
   void    bawrite(struct buf *);
   void    babarrierwrite(struct buf *);
   int     bbarrierwrite(struct buf *);
   void    bdirty(struct buf *);
   void    bundirty(struct buf *);
   void    bufstrategy(struct bufobj *, struct buf *);
   void    brelse(struct buf *);
   void    bqrelse(struct buf *);
   int     vfs_bio_awrite(struct buf *);
   void    vfs_drain_busy_pages(struct buf *bp);
   struct buf *     getpbuf(int *);
   struct buf *incore(struct bufobj *, daddr_t);
   struct buf *gbincore(struct bufobj *, daddr_t);
   struct buf *getblk(struct vnode *, daddr_t, int, int, int, int);
   struct buf *geteblk(int, int);
   int     bufwait(struct buf *);
   int     bufwrite(struct buf *);
   void    bufdone(struct buf *);
   void    bufdone_finish(struct buf *);
   void    bd_speedup(void);
   
   int     cluster_read(struct vnode *, u_quad_t, daddr_t, long,
               struct ucred *, long, int, int, struct buf **);
   int     cluster_wbuild(struct vnode *, long, daddr_t, int, int);
   void    cluster_write(struct vnode *, struct buf *, u_quad_t, int, int);
   void    vfs_bio_bzero_buf(struct buf *bp, int base, int size);
   void    vfs_bio_set_valid(struct buf *, int base, int size);
   void    vfs_bio_clrbuf(struct buf *);
   void    vfs_busy_pages(struct buf *, int clear_modify);
   void    vfs_unbusy_pages(struct buf *);
   int     vmapbuf(struct buf *, int);
   void    vunmapbuf(struct buf *);
   void    relpbuf(struct buf *, int *);
   void    brelvp(struct buf *);
   void    bgetvp(struct vnode *, struct buf *);
   void    pbgetbo(struct bufobj *bo, struct buf *bp);
   void    pbgetvp(struct vnode *, struct buf *);
   void    pbrelbo(struct buf *);
   void    pbrelvp(struct buf *);
   int     allocbuf(struct buf *bp, int size);
   void    reassignbuf(struct buf *);
   struct  buf *trypbuf(int *);
   void    bwait(struct buf *, u_char, const char *);
   void    bdone(struct buf *);
   void    bpin(struct buf *);
   void    bunpin(struct buf *);
   void    bunpin_wait(struct buf *);
   
   #endif /* _KERNEL */
   
   #endif /* !_SYS_BUF_H_ */

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