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bio_alloc_bioset(9) [centos man page]

BIO_ALLOC_BIOSET(9)						   The Linux VFS					       BIO_ALLOC_BIOSET(9)

NAME
bio_alloc_bioset - allocate a bio for I/O SYNOPSIS
struct bio * bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set * bs); ARGUMENTS
gfp_mask the GFP_ mask given to the slab allocator nr_iovecs number of iovecs to pre-allocate bs the bio_set to allocate from. DESCRIPTION
If bs is NULL, uses kmalloc to allocate the bio; else the allocation is backed by the bs's mempool. When bs is not NULL, if __GFP_WAIT is set then bio_alloc will always be able to allocate a bio. This is due to the mempool guarantees. To make this work, callers must never allocate more than 1 bio at a time from this pool. Callers that need to allocate more than 1 bio must always submit the previously allocated bio for IO before attempting to allocate a new one. Failure to do so can cause deadlocks under memory pressure. Note that when running under generic_make_request (i.e. any block driver), bios are not submitted until after you return - see the code in generic_make_request that converts recursion into iteration, to prevent stack overflows. This would normally mean allocating multiple bios under generic_make_request would be susceptible to deadlocks, but we have deadlock avoidance code that resubmits any blocked bios from a rescuer thread. However, we do not guarantee forward progress for allocations from other mempools. Doing multiple allocations from the same mempool under generic_make_request should be avoided - instead, use bio_set's front_pad for per bio allocations. RETURNS
Pointer to new bio on success, NULL on failure. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 BIO_ALLOC_BIOSET(9)

Check Out this Related Man Page

PROBE::IOBLOCK_TRACE(3stap)				  IO Scheduler and block IO Taps			       PROBE::IOBLOCK_TRACE(3stap)

NAME
probe::ioblock_trace.bounce - Fires whenever a buffer bounce is needed for at least one page of a block IO request. SYNOPSIS
ioblock_trace.bounce VALUES
None DESCRIPTION
name - name of the probe point q - request queue on which this bio was queued. devname - device for which a buffer bounce was needed. ino - i-node number of the mapped file bytes_done - number of bytes transferred sector - beginning sector for the entire bio flags - see below BIO_UPTODATE 0 ok after I/O completion BIO_RW_BLOCK 1 RW_AHEAD set, and read/write would block BIO_EOF 2 out-out-bounds error BIO_SEG_VALID 3 nr_hw_seg valid BIO_CLONED 4 doesn't own data BIO_BOUNCED 5 bio is a bounce bio BIO_USER_MAPPED 6 contains user pages BIO_EOPNOTSUPP 7 not supported rw - binary trace for read/write request vcnt - bio vector count which represents number of array element (page, offset, length) which makes up this I/O request idx - offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed. size - total size in bytes bdev - target block device bdev_contains - points to the device object which contains the partition (when bio structure represents a partition) p_start_sect - points to the start sector of the partition structure of the device CONTEXT
The process creating a block IO request. SystemTap Tapset Reference June 2014 PROBE::IOBLOCK_TRACE(3stap)

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