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blk_make_request(9) [centos man page]

BLK_MAKE_REQUEST(9)						   Block Devices					       BLK_MAKE_REQUEST(9)

blk_make_request - given a bio, allocate a corresponding struct request. SYNOPSIS
struct request * blk_make_request(struct request_queue * q, struct bio * bio, gfp_t gfp_mask); ARGUMENTS
q target request queue bio The bio describing the memory mappings that will be submitted for IO. It may be a chained-bio properly constructed by block/bio layer. gfp_mask gfp flags to be used for memory allocation DESCRIPTION
blk_make_request is the parallel of generic_make_request for BLOCK_PC type commands. Where the struct request needs to be farther initialized by the caller. It is passed a struct bio, which describes the memory info of the I/O transfer. The caller of blk_make_request must make sure that bi_io_vec are set to describe the memory buffers. That bio_data_dir will return the needed direction of the request. (And all bio's in the passed bio-chain are properly set accordingly) If called under none-sleepable conditions, mapped bio buffers must not need bouncing, by calling the appropriate masked or flagged allocator, suitable for the target device. Otherwise the call to blk_queue_bounce will BUG. WARNING
When allocating/cloning a bio-chain, careful consideration should be given to how you allocate bios. In particular, you cannot use __GFP_WAIT for anything but the first bio in the chain. Otherwise you risk waiting for IO completion of a bio that hasn't been submitted yet, thus resulting in a deadlock. Alternatively bios should be allocated using bio_kmalloc instead of bio_alloc, as that avoids the mempool deadlock. If possible a big IO should be split into smaller parts when allocation fails. Partial allocation should not be an error, or you risk a live-lock. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 BLK_MAKE_REQUEST(9)

Check Out this Related Man Page

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

probe::ioblock_trace.end - Fires whenever a block I/O transfer is complete. SYNOPSIS
ioblock_trace.end VALUES
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 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 signals the transfer is done. SystemTap Tapset Reference June 2014 PROBE::IOBLOCK_TRACE(3stap)

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