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From: Bart Van Assche <bvanassche@acm.org>
To: Bodo Stroesser <bostroesser@gmail.com>, Christoph Hellwig <hch@lst.de>
Cc: Joel Becker <jlbec@evilplan.org>,
	linux-kernel@vger.kernel.org,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	Yanko Kaneti <yaneti@declera.com>,
	Brendan Higgins <brendanhiggins@google.com>
Subject: Re: [PATCH 2/4] configfs: Fix writing at a non-zero offset
Date: Mon, 26 Jul 2021 20:17:33 -0700	[thread overview]
Message-ID: <ab190c50-8c87-b215-1432-056c81bcd656@acm.org> (raw)
In-Reply-To: <c9cb1f3b-0b3b-c571-4a51-e647f3c1e90a@gmail.com>

On 7/26/21 5:54 PM, Bodo Stroesser wrote:
> The new behavior can also cause trouble with existing store handlers.
> Example:
> The tcmu attribute files cmd_time_out and qfull_time_out just take a
> string containing the decimal formatted number of seconds of the
> timeout. Each number up to now had to be transferred in a single write.
> Assume the old value is 30 and we want to change to 19. If userspace
> writes byte by byte, you end up calling
> store(item, "1\0", 1) and then
> store(item, "19\9", 2).
> If these quick changes do not cause trouble in tcmu's scsi cmd handling,
> then think what happens, if userspace is interrupted between the two
> writes. Allowing to split the writes cause a loss of "atomicity".

From Documentation/filesystems/configfs.rst, for normal attributes:
"Configfs expects write(2) to store the entire buffer at once." In other
words, the behavior for partial writes is undocumented. My changes
preserve the behavior if a buffer is written in its entirety. I do not
agree that my changes can cause trouble for existing store handlers.

Bart.

  reply	other threads:[~2021-07-27  3:17 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 21:23 [PATCH 0/4] Improve the configfs read and write iterators further Bart Van Assche
2021-07-23 21:23 ` [PATCH 1/4] configfs: Rework the overflow check in fill_write_buffer() Bart Van Assche
2021-07-23 21:23 ` [PATCH 2/4] configfs: Fix writing at a non-zero offset Bart Van Assche
2021-07-26 14:58   ` Bodo Stroesser
2021-07-26 16:26     ` Bart Van Assche
2021-07-26 21:13       ` Bodo Stroesser
2021-07-26 21:52         ` Bart Van Assche
2021-07-27  0:54           ` Bodo Stroesser
2021-07-27  3:17             ` Bart Van Assche [this message]
2021-07-27  7:27               ` Bodo Stroesser
2021-07-27 16:47                 ` Bart Van Assche
2021-07-28 17:14                   ` Bodo Stroesser
2021-07-28 17:55                     ` Bart Van Assche
2021-07-23 21:23 ` [PATCH 3/4] kunit: Add support for suite initialization and cleanup Bart Van Assche
2021-07-27 21:26   ` Brendan Higgins
2021-07-29  3:33     ` Bart Van Assche
2021-07-23 21:23 ` [PATCH 4/4] configfs: Add unit tests Bart Van Assche

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