Boaz Harrosh wrote:
Douglas Gilbert <dougg@xxxxxxxxxx> wrote ...
struct sg_io_v4 {
__s32 guard; /* [i] 'Q' to differentiate from v3 */
__u32 protocol; /* [i] 0 -> SCSI , .... */
__u32 subprotocol; /* [i] 0 -> SCSI command, 1 -> SCSI task
management function, .... */
__u32 request_len; /* [i] in bytes */
__u64 request; /* [i], [*i] {SCSI: cdb} */
__u64 request_tag; /* [i] {SCSI: task tag (only if flagged)} */
__u32 request_attr; /* [i] {SCSI: task attribute} */
__u32 request_priority; /* [i] {SCSI: task priority} */
__u32 request_extra; /* [i] {spare, for padding} */
__u32 max_response_len; /* [i] in bytes */
__u64 response; /* [i], [*o] {SCSI: (auto)sense data} */
/* "dout_": data out (to device); "din_": data in (from device) */
__u32 dout_iovec_count; /* [i] 0 -> "flat" dout transfer else
dout_xfer points to array of iovec */
__u32 dout_xfer_len; /* [i] bytes to be transferred to device */
__u32 din_iovec_count; /* [i] 0 -> "flat" din transfer */
__u32 din_xfer_len; /* [i] bytes to be transferred from device */
__u64 dout_xferp; /* [i], [*i] */
__u64 din_xferp; /* [i], [*o] */
__u32 timeout; /* [i] units: millisecond */
__u32 flags; /* [i] bit mask */
__u64 usr_ptr; /* [i->o] unused internally */
__u32 spare_in; /* [i] */
...
Currently because of a twisted accident sg and bsg queue their async
request with the "at_head" flag set when calling blk_execute_rq_nowait.
Since sg_io_v4 is new and as plenty of possible choices, what would be
the best place to put the "at_head" flag?
Douglas ?
What was your intention with the above:
__u32 request_priority; /* [i] {SCSI: task priority} */
[And while at it, what was:
__u32 request_attr; /* [i] {SCSI: task attribute} */
Yes, task attribute. That is the term used by SAM-4
(and earlier). Unfortunately SAM-4 defines the names
but not values; those values are left up to the
transport. That presents a problem for a transport
agnostic SCSI pass-through interface like sg_io_v4.
For backward compatibility we probably need to make the value
0 mean "head of queue" (or whatever the mid-level default
task attribute is for pass-through SCSI commands).
Also we probably don't have a clean pass-through of task
attributes in the SCSI mid-level currently. I mean "clean"
in the sense of "leave them alone" and do not act on the
command completion status (e.g. TASK SET FULL).
Should I define (bsg.h):
enum {
BSG_AT_HEAD = 0, /* compatible with old code */
BSG_AT_TAIL,
}
And put it in request_priority
or (adding "_TA_" for task attribute):
enum {
BSG_TA_DEFAULT = 0, // lk 2.4, 2.6 series: head of queue
BSG_TA_HEAD_OF_Q = 0x1000,
BSG_TA_SIMPLE,
BSG_TA_ORDERED,
BSG_TA_ACA,
....
or define:
#define SG_FLAG_AT_TAIL 0x10 /* See sg.h for more/other flags (sg.h flags are ignored by bsg) */
And OR that into the old flags member that is otherwise
unused by current bsg code
I would prefer using the request_attr field.
Tomo, what do you think?
Doug Gilbert
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