BLK_QUEUE_MERGE_BVEC(9) Block Devices BLK_QUEUE_MERGE_BVEC(9)NAME
blk_queue_merge_bvec - set a merge_bvec function for queue
SYNOPSIS
void blk_queue_merge_bvec(struct request_queue * q, merge_bvec_fn * mbfn);
ARGUMENTS
q
queue
mbfn
merge_bvec_fn
DESCRIPTION
Usually queues have static limitations on the max sectors or segments that we can put in a request. Stacking drivers may have some settings
that are dynamic, and thus we have to query the queue whether it is ok to add a new bio_vec to a bio at a given offset or not. If the block
device has such limitations, it needs to register a merge_bvec_fn to control the size of bio's sent to it. Note that a block device *must*
allow a single page to be added to an empty bio. The block device driver may want to use the bio_split function to deal with these bio's.
By default no merge_bvec_fn is defined for a queue, and only the fixed limits are honored.
COPYRIGHT Kernel Hackers Manual 2.6. July 2010 BLK_QUEUE_MERGE_BVEC(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.request - Fires just as a generic block I/O request is created for a bio.
SYNOPSIS
ioblock_trace.request
VALUES
None
DESCRIPTION
name - name of the probe point q - request queue on which this bio was queued. devname - block device name 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 make
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 makes block I/O request
SystemTap Tapset Reference June 2014 PROBE::IOBLOCK_TRACE(3stap)
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