Re: Problem with Samba re-share of a CIFS mount

[Gionatan Danti <g.danti-N44kj/XGErOonA0d6jMUrA@public.gmane.org>]

Hi Jeff,
I had the same idea.

When mounting the CIFS directory, the problematic installations return 0 
links for both dirs and files. On the other hand, the stock CentOS 
installation return 1 or more links.

It puzzled me. Two questions:
- anyone know the rationale behind this?
- how it is possible to work-around that with an unpatched kernel?

Thank you and regards.

On 02/11/2014 04:33 PM, Jeff Layton wrote:
> On Tue, 11 Feb 2014 10:30:13 +0100
> Gionatan Danti <g.danti-N44kj/XGErOonA0d6jMUrA@public.gmane.org> wrote:
>
>> Hi all,
>> I have a strange problem trying to re-share, via Samba, a CIFS mount.
>>
>> Let first explain my network topology:
>>
>> Win2008R2 w/SMB share -> low speed link -> Linux Box -> WIN7 clients
>>
>> In short, a Win2008 R2 share is being accessed by some W7 clients over a
>> slow (~8 Mb/s downstream, ~1 Mb/s upstream) ADSL link. To speed up read
>> operation on the branch office, I thought to use a Linux Box with
>> cachefilesd and a CONFIG_CIFS_FSCACHE enabled kernel. The Linux box will
>> mount the Win2008R2 share and, thanks to cachefilesd, it will maintain
>> an "hot cache" of the read data. This CIFS mount is then shared, via
>> Samba, to the other client Win7 PCs.
>>
>> However, the problem is that when re-sharing the CIFS mount, the Win7
>> clients often see the many directories inside the mount as a regular
>> files, and not directories! In other words, if I have a directory "test"
>> inside the mount, the client PC will see a _file_ called "test". When
>> double-clicking on that "file", the Win7 client even ask to select the
>> application to open it.
>>
>> The strange this is that this problem happen with some Linux kernel
>> version, but not with others. These are my results:
>>
>> 1) Stock CentOS 6.5 x86-64 system (kernel 2.6.32-431.1.2.0.1, cifs-utils
>> 4.8.1-19, samba 3.6.9-167): no problem here, but this kernel does not
>> have CONFIG_CIFS_FSCACHE, so I can not use it for speeding up read access;
>>
>> 2) CentOS 6.5 x86-64 with ElRepo updates (kernel 3.10.28-1): here
>> CONFIG_CIFS_FSCACHE is enabled, but I have the problem described above;
>>
>> 3) Debian 7 amd64 with latest updates (kernel 3.2.54-2, cifs-utils
>> 2:5.5-1): CONFIG_CIFS_FSCACHE is enabled, problem happens;
>>
>> 4) Fedora 20 x86-64 (kernel 3.12.8-300, cifs-utils 6.3-1, samba
>> 4.1.3-2): CONFIG_CIFS_FSCACHE is enabled and problem does _not_ happen,
>> however this is a client distro and I am not so comfortable to put it
>> into production.
>>
>> Anyone has any explanation of what is happening here?
>> Regards.
>>
>
> Most likely, the problem is that the cifs mount is returning an
> st_nlink value of 0 for directories, and that confuses samba into
> thinking that directories are files (I forget their rationale for this).
>
> More recent kernels have patches that make the client fake up st_nlink
> values when the server sends 0 for a NumberOfLinks value.
>

-- 
Danti Gionatan
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