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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/uapi | |
| 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/uapi')
| -rw-r--r-- | include/uapi/linux/bsg.h | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/include/uapi/linux/bsg.h b/include/uapi/linux/bsg.h index 7a12e1c0f371..02986cf8b6f1 100644 --- a/include/uapi/linux/bsg.h +++ b/include/uapi/linux/bsg.h @@ -10,12 +10,13 @@ #define BSG_SUB_PROTOCOL_SCSI_TRANSPORT 2 /* - * For flags member below - * sg.h sg_io_hdr also has bits defined for it's flags member. However - * none of these bits are implemented/used by bsg. The bits below are - * allocated to not conflict with sg.h ones anyway. + * For flag constants below: + * sg.h sg_io_hdr also has bits defined for it's flags member. These + * two flag values (0x10 and 0x20) have the same meaning in sg.h . For + * bsg the BSG_FLAG_Q_AT_HEAD flag is ignored since it is the deafult. */ -#define BSG_FLAG_Q_AT_TAIL 0x10 /* default, == 0 at this bit, is Q_AT_HEAD */ +#define BSG_FLAG_Q_AT_TAIL 0x10 /* default is Q_AT_HEAD */ +#define BSG_FLAG_Q_AT_HEAD 0x20 struct sg_io_v4 { __s32 guard; /* [i] 'Q' to differentiate from v3 */ |