Reproducible Data Corruption Issue

Volker Lendecke Volker.Lendecke at SerNet.DE
Thu Oct 9 12:21:53 MDT 2014

On Thu, Oct 09, 2014 at 09:16:42AM -0700, Jeremy Allison wrote:
> Looking at this report in more detail, it looks like
> the (extremely rare) case of accessing a
> file using 2 protocols simultaneously,
> the protocols being CIFS and ftp.
> If you're doing this:
> 1). Turn off oplocks. You need to
> set "oplocks = no" on that share
> if you expect to see *any* consistency
> between the ftp client and the Linux
> CIFS client. Otherwise all bets are
> off (the Linux CIFS client code will
> cache up the wazoo, which is what
> the report seems to be complaining
> about :-).
> 2). The report seems to be expecting
> fcntl byte range locks to save them.
> ftp clients don't issue byte range
> lock requests - they ignore them.
> If you need true cross-protocol
> synchronization, turn off oplocks
> and ensure the byte ranges you're
> accessing are locked by *both*
> protocols.
> IMHO this doesn't look like a
> Samba bug, but a config (and
> expectations) error.

I'd call this some unexpected behaviour (bug) of the Linux cifs client
with Samba. My understanding of the document is that the target file is
only being accessed via Samba, both ftp clients come in via a Linux cifs
mount. If that is a misunderstanding on my side, please correct me.

I believe this *should* work and not cause corruption. It would be
interesting to me to see the full logs and network traces, if possible
together with an strace -ttT of both ftp server processes.

With best regards,

Volker Lendecke

SerNet GmbH, Bahnhofsallee 1b, 37081 Göttingen
phone: +49-551-370000-0, fax: +49-551-370000-9
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