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SubjectRe: [PATCH] queue barrier support
On Wed, Feb 13 2002, Martin Dalecki wrote:
> >On Wed, Feb 13 2002, Martin Dalecki wrote:
> >
> >>Jens Axboe wrote:
> >>
> >>>Patches attached, comments welcome.
> >>>
> >>>diff -Nru a/include/linux/ide.h b/include/linux/ide.h
> >>>--- a/include/linux/ide.h Wed Feb 13 13:48:25 2002
> >>>+++ b/include/linux/ide.h Wed Feb 13 13:48:25 2002
> >>>@@ -448,6 +448,7 @@
> >>> byte acoustic; /* acoustic management */
> >>> unsigned int failures; /* current failure count */
> >>> unsigned int max_failures; /* maximum allowed failure count */
> >>>+ char special_buf[4]; /* IDE_DRIVE_CMD, free use */
> >>>} ide_drive_t;
> >>>
> >>ide-barrier-1-c1.296:+ memset(drive->special_buf, 0,
> >>sizeof(drive->special_buf));
> >>ide-barrier-1-c1.296:+ flush_rq->buffer = drive->special_buf;
> >>ide-barrier-1-c1.296:+ char special_buf[4]; /*
> >>IDE_DRIVE_CMD, free use */
> >>
> >>I just don't see special_buf used anywhere. What is it supposed to be
> >>used for?
> >>Is the intention to make it look like the SCSI code?
> >>
> >
> >See ide.c:ide_queue_flush_cmd(), I'm only using 1 of the bytes but it
> >has room for 4 like that is typically used when issuing an ata command
> >directly. So yes, it is used, I'm not adding stuff for fun :-)
> >
>
> OK I see now. Is this to become analogous to the sr_cmnd field for
> struct scsi_request?
> It would make sense to first make them use the same software
> architecture at least and then
> to merge as much of this driver mid-layer stuff as possible....

Well dunno, typically users of IDE_DRIVE_CMD's are using ide_wait and
thus waits for completion. So request and arguments are almost always
allocated on the stack, which is fine in that case. For out-of-order
execution like the pre and post flushes in the barrier patch, there just
needed to be some bytes available for the data command.

The SCSI sr_cmnd[] cdb is different from the ATA register set, but in
fact in 2.5 the IDE layer could use the cdb in struct request as a temp
buffer for stuff like this. It's exactly what the ide-barrier patch
above could use. So yeah I could clean special_buf[] and just use

rq->buffer = rq->cmd;

instead.

--
Jens Axboe

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