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| author | Douglas Gilbert <dgilbert@interlog.com> | 2014-07-01 10:48:05 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2014-07-01 10:48:05 -0600 |
| commit | d15156138dad40205c9fdd9abe85c9e1479ae272 (patch) | |
| tree | 714db80059b08f75e86adb31aa61bdcfa9d286c6 /include/scsi/sg.h | |
| parent | 9b4231bf995996d6459c57959ead5a1829ff2c57 (diff) | |
| download | linux-d15156138dad40205c9fdd9abe85c9e1479ae272.tar.gz linux-d15156138dad40205c9fdd9abe85c9e1479ae272.tar.bz2 linux-d15156138dad40205c9fdd9abe85c9e1479ae272.zip | |
block SG_IO: add SG_FLAG_Q_AT_HEAD flag
After the SG_IO ioctl was copied into the block layer and
later into the bsg driver, subtle differences emerged.
One difference is the way injected commands are queued through
the block layer (i.e. this is not SCSI device queueing nor SATA
NCQ). Summarizing:
- SG_IO on block layer device: blk_exec*(at_head=false)
- sg device SG_IO: at_head=true
- bsg device SG_IO: at_head=true
Some time ago Boaz Harrosh introduced a sg v4 flag called
BSG_FLAG_Q_AT_TAIL to override the bsg driver default. A
recent patch titled: "sg: add SG_FLAG_Q_AT_TAIL flag"
allowed the sg driver default to be overridden. This patch
allows a SG_IO ioctl sent to a block layer device to have
its default overridden.
ChangeLog:
- introduce SG_FLAG_Q_AT_HEAD flag in sg.h to cause
commands that are injected via a block layer
device SG_IO ioctl to set at_head=true
- make comments clearer about queueing in sg.h since the
header is used both by the sg device and block layer
device implementations of the SG_IO ioctl.
- introduce BSG_FLAG_Q_AT_HEAD in bsg.h for compatibility
(it does nothing) and update comments.
Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include/scsi/sg.h')
| -rw-r--r-- | include/scsi/sg.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/scsi/sg.h b/include/scsi/sg.h index a9f3c6fc3f57..4734c15ab5d6 100644 --- a/include/scsi/sg.h +++ b/include/scsi/sg.h @@ -129,6 +129,9 @@ typedef struct sg_io_hdr #define SG_FLAG_MMAP_IO 4 /* request memory mapped IO */ #define SG_FLAG_NO_DXFER 0x10000 /* no transfer of kernel buffers to/from */ /* user space (debug indirect IO) */ +/* defaults:: for sg driver: Q_AT_HEAD; for block layer: Q_AT_TAIL */ +#define SG_FLAG_Q_AT_TAIL 0x10 +#define SG_FLAG_Q_AT_HEAD 0x20 /* following 'info' values are "or"-ed together */ #define SG_INFO_OK_MASK 0x1 |