Re: [PATCH v4] sg: O_EXCL and other lock handling

[Hannes Reinecke <hare@suse.de>]

On 06/13/2014 02:26 AM, Douglas Gilbert wrote:
> This is a re-presentation of a patch to the sg driver
> whose v3 was sent in November 2013:
>    http://www.spinics.net/lists/linux-scsi/msg69957.html
>
> It addresses a problem reported by Vaughan Cao concerning
> the correctness of the O_EXCL logic in the sg driver. POSIX
> doesn't defined O_EXCL semantics on devices but "allow only
> one open file descriptor at a time per sg device" is a rough
> definition. The sg driver's semantics have been to wait
> on an open() when O_NONBLOCK is not given and there are
> O_EXCL headwinds. Nasty things can happen during that wait
> such as the device being detached (removed). So multiple
> locks are reworked in this patch making it large and hard
> to break down into digestible bits.
>
> This patch is against Linus's current git repository which
> doesn't include any sg patches sent in the last few weeks.
> Hence this patch touches as little as possible that it
> doesn't need to and strips out most SCSI_LOG_TIMEOUT()
> changes in v3 because Hannes said he was going to rework all
> that stuff.
>
> The sg3_utils package has several test programs written to
> test this patch. See examples/sg_tst_excl*.cpp .
>
> Not all the locks and flags in sg have been re-worked in
> this patch, notably sg_request::done . That can wait for
> a follow-up patch if this one meets with approval.
>
> ChangeLog v4:
>    - based on the current kernel tree: pre 3.16-rc1
>    - strip out clean-ups in v3 that others are better
>      placed to do (e.g. debug/logging)
>    - simplify open_wait_event() logic and add comment
>
> ChangeLog v3 and earlier: see link in the first paragraph.
>
>
> Could anyone confirm whether v3 of this patch has found its
> way into any distro and/or been tested or used more widely?
>
> Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
>
>
We've tested a similar version here.

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
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