[Samba] Overwriting open files on cifs mount of Samba share fails

[Philipp Wendler]

Hi,

Am 05.11.21 um 23:06 schrieb Jeremy Allison via samba:
> On Fri, Nov 05, 2021 at 08:14:02PM +0100, Philipp Wendler via samba wrote:
>> I have tested this among others with Ubuntu 20.04 on both client and
>> server (kernel 5.4.0 and samba 4.11.6). I am aware that these are not
>> the latest versions, but as mentioned would greatly appreciate any
>> information about whether an update could potentially improve the
>> situation.
>> My configuration is totally standard as I tested it with a fresh
>> installation and just added a writable share.
>> The resulting mount options on the client are
>> rw,relatime,vers=3.1.1,cache=strict,uid=1000,noforceuid,gid=1000,noforcegid,
>> file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,
>> rsize=4194304,wsize=4194304,bsize=1048576,echo_interval=60,actimeo=1
>> Of these, I only specified vers, uid and gid.
>> nounix was automatically added although testparm -v on the server says
>> "unix extensions = Yes".
> 
> "unix extensions" only works over SMB1 at the moment. You
> have specified SMB version 3.1.1 in your mount options on
> the client, plus friends don't let friends use SMB1 anymore
> (and your server almost certainly has SMB1 disabled).

I actually set vers=3.1.1 because the mount.cifs man page says that
either SBM1 or SMB3.1.1 is required for the unix extensions,
and I am aware that I do not want SMB1 :-)
https://git.samba.org/?p=cifs-utils.git;a=blob;f=mount.cifs.rst;h=9d4446f035b6865e2cce5cf8d550ef84a5823607;hb=HEAD#l479

But of course this won't help if the server does not support it.
May I suggest to add the information that SMB1 is required to
https://www.samba.org/samba/docs/current/man-html/smb.conf.5.html#UNIXEXTENSIONS
to make this clear?

> The client redirector will have to try and spoof this,
> rename over open files can't be done with "standard"
> SMB2+.

Thank you very much for the explanation!
Knowing that my use case would require unix extensions but these are
currently not usable is exactly the kind of information I was looking
for. So I will switch to a different network protocol.

Kind regards
Philipp