probe::ioblock_trace.bounce(3stap) [centos 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)

BLK_MAKE_REQUEST(9)						   Block Devices					       BLK_MAKE_REQUEST(9)

NAME

       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)