bread(vp, blkno, size, cred, flags, bpp)
Read a block corresponding to
vp and
blkno. The buffer is returned via
bpp. The units of
blkno are specifically the units used by the
VOP_STRATEGY() routine for the
vp vnode. For device special files,
blkno is in units of
DEV_BSIZE and both
blkno and
size must be multiples of the underlying device's block size. For other files,
blkno is in units chosen by the file system containing
vp.
If the buffer is not found (i.e. the block is not cached in memory),
bread() allocates a buffer with enough pages for
size and reads the specified disk block into it using credential
cred.
The buffer returned by
bread() is marked as busy. (The
B_BUSY flag is set.) After manipulation of the buffer returned from
bread(), the caller should unbusy it so that another thread can get it. If the buffer contents are modified and should be written back to disk, it should be unbusied using one of variants of
bwrite(). Otherwise, it should be unbusied using
brelse().
breadn(vp, blkno, size, rablks, rasizes, nrablks, cred, flags, bpp)
Get a buffer as bread(). In addition, breadn() will start read-ahead of blocks specified by rablks, rasizes, nrablks.
breada(vp, blkno, size, rablkno, rabsize, cred, flags, bpp)
Same as breadn() with single block read-ahead. This function is for compatibility with old filesystem code and shouldn't be used by new ones.
bwrite(bp)
Write a block. Start I/O for write using VOP_STRATEGY(). Then, unless the B_ASYNC flag is set in bp, bwrite() waits for the I/O to complete.
bawrite(bp)
Write a block asynchronously. Set the B_ASYNC flag in bp and simply call VOP_BWRITE(), which results in bwrite() for most filesystems.
bdwrite(bp)
Delayed write. Unlike bawrite(), bdwrite() won't start any I/O. It only marks the buffer as dirty (B_DELWRI) and unbusy it.
getblk(vp, blkno, size, slpflag, slptimeo)
Get a block of requested size
size that is associated with a given vnode and block offset, specified by
vp and
blkno. If it is found in the block cache, make it busy and return it. Otherwise, return an empty block of the correct size. It is up to the caller to ensure that the cached blocks are of the correct size.
If
getblk() needs to sleep,
slpflag and
slptimeo are used as arguments for
cv_timedwait().
geteblk(size)
Allocate an empty, disassociated block of a given size size.
incore(vp, blkno)
Determine if a block associated to a given vnode and block offset is in the cache. If it is there, return a pointer to it. Note that incore() doesn't busy the buffer unlike getblk().
allocbuf(bp, size, preserve)
Expand or contract the actual memory allocated to a buffer. If preserve is zero, the entire data in the buffer will be lost. Otherwise, if the buffer shrinks, the truncated part of the data is lost, so it is up to the caller to have written it out first if needed; this routine will not start a write. If the buffer grows, it is the callers responsibility to fill out the buffer's additional contents.
brelse(bp, set)
Unbusy a buffer and release it to the free lists.
biodone(bp)
Mark I/O complete on a buffer. If a callback has been requested by B_CALL, do so. Otherwise, wakeup waiters.
biowait(bp)
Wait for operations on the buffer to complete. When they do, extract and return the I/O's error value.