From: Jeremy Allison <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Pavel Begunkov <[email protected]>,
Stefan Metzmacher <[email protected]>,
io-uring <[email protected]>,
Samba Technical <[email protected]>,
[email protected]
Subject: Re: Data Corruption bug with Samba's vfs_iouring and Linux 5.6.7/5.7rc3
Date: Thu, 7 May 2020 11:31:40 -0700 [thread overview]
Message-ID: <20200507183140.GD25085@jeremy-acer> (raw)
In-Reply-To: <[email protected]>
On Thu, May 07, 2020 at 10:50:40AM -0600, Jens Axboe wrote:
> On 5/7/20 10:48 AM, Jeremy Allison wrote:
> > On Thu, May 07, 2020 at 10:43:17AM -0600, Jens Axboe wrote:
> >>
> >> Just like for regular system calls, applications must be able to deal
> >> with short IO.
> >
> > Thanks, that's a helpful definitive reply. Of course, the SMB3
> > protocol is designed to deal with short IO replies as well, and
> > the Samba and linux kernel clients are well-enough written that
> > they do so. MacOS and Windows however..
>
> I'm honestly surprised that such broken clients exists! Even being
> a somewhat old timer cynic...
>
> > Unfortunately they're the most popular clients on the planet,
> > so we'll probably have to fix Samba to never return short IOs.
>
> That does sound like the best way forward, short IOs is possible
> with regular system calls as well, but will definitely be a lot
> more frequent with io_uring depending on the access patterns,
> page cache, number of threads, and so on.
OK, I just want to be *REALLY CLEAR* what you're telling me
(I've already written the pread/pwrite wrappers for Samba
that deal with short IO but want to ensure I understand
fully before making any changes to Samba).
You're saying that on a bog-standard ext4 disk file:
ret = pread(fd, buf, count, offset);
can return *less* than count bytes if there's no IO
error and the file size is greater than offset+count
and no one else is in the middle of a truncate etc. ?
And:
ret = pwrite(fd, buf, count, offset);
can return less* than count bytes if there's no IO
error and there's ample space on disk ?
I have to say I've *never* seen that happen, and
Samba is widely enough used that IO corruption from
short reads/writes from MacOSX and Windows clients
would have been widely reported by now.
Look at how quickly someone spotted disk corruption
because of the change in userspace-visible behavior
of the io_uring interface. We only shipped that code
03 March 2020 and someone *already* found it.
Jeremy.
next prev parent reply other threads:[~2020-05-07 18:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 10:04 Data Corruption bug with Samba's vfs_iouring and Linux 5.6.7/5.7rc3 Stefan Metzmacher
2020-05-05 14:41 ` Jens Axboe
2020-05-05 15:44 ` Jens Axboe
2020-05-05 16:53 ` Jens Axboe
2020-05-05 17:39 ` Jens Axboe
2020-05-05 17:48 ` Jeremy Allison
2020-05-05 17:50 ` Jens Axboe
[not found] ` <[email protected]>
2020-05-06 10:33 ` Stefan Metzmacher
2020-05-06 10:41 ` Stefan Metzmacher
[not found] ` <[email protected]>
2020-05-06 14:08 ` Stefan Metzmacher
2020-05-06 14:43 ` Andreas Schneider
2020-05-06 14:46 ` Andreas Schneider
2020-05-06 15:06 ` Stefan Metzmacher
2020-05-06 17:03 ` Jeremy Allison
2020-05-06 17:13 ` Jeremy Allison
2020-05-06 18:01 ` Jeremy Allison
2020-05-05 20:19 ` Stefan Metzmacher
2020-05-06 12:55 ` Pavel Begunkov
2020-05-06 15:20 ` Stefan Metzmacher
2020-05-06 15:42 ` Pavel Begunkov
2020-05-07 16:43 ` Jens Axboe
2020-05-07 16:48 ` Jeremy Allison
2020-05-07 16:50 ` Jens Axboe
2020-05-07 18:31 ` Jeremy Allison [this message]
2020-05-07 18:35 ` Jens Axboe
2020-05-07 18:55 ` Jeremy Allison
2020-05-07 18:58 ` Jens Axboe
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