Re: DFS with unix extensions or mfsymlinks/SFU

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On Fri, 2014-04-04 at 12:44 +0200, Tobias Doerffel wrote:
> Hi,
> 
> we recently deployed a DFS setup based on Samba 4. Things are working well on Windows computers while we have some troubles with our Linux terminal servers.
> 
> Our company's DFS tree is mounted at /dfs using sec=krb and the multiuser option. As soon as there are DFS links we get the famous
> 
> ls: cannot read symbolic link FOOBAR: Object is remote
> 
> message. However we can chdir into the directory (and display its contents) even though it sometimes doesn't work immediately. When I however disable unix extensions (-o nounix) I don't have these issues and DFS referrals get resolved/mounted immediately, that's why we currently use this option. However disabling unix extensions is not an option long term as our users need software which creates e.g. pipes/FIFOs, does file locking etc. and worked well before (with OpenAFS). This could be achieved by using the «sfu» option. But if I enable SFU support, I can neither create symlinks nor use the mfsymlinks mount option. So whatever approach I chose, there's always something not working properly.
> 
> Do you have any advice? Is there any reason why SFU does not work in conjunction with MFSymLinks?
> 

Hello Tobais,

The following patch should help you.
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=924e3fa48c627ad45d3be9412a93df34ab0fb482

This is probably not yet included in the kernel you are using. Maybe you
can try recompiling your kernel with this patch included and see if it
helps you.

Regards
Sachin Prabhu

> More information:
> 
> Mount options used:
> - mostly working DFS setup without unix extensions: sec=krb5,nounix,multiuser,mfsymlinks,dir_mode=0700,file_mode=0700,noserverino,cache=strict,mapchars,rsize=16777216,wsize=16777216,nobrl
> 
> - Simple test setup with unix extensions:
> sec=krb5,multiuser,cache=strict
> 
> System: Ubuntu 12.04.4 LTS x86_64
> Kernel version: 3.13.6 (current  Ubuntu 14.04 kernel)
> CIFS utils: 6.3
> Keyutils: 1.5.9
> 
> # grep CIFS /boot/config-3.13.0-21-generic 
> CONFIG_CIFS=m
> CONFIG_CIFS_STATS=y
> # CONFIG_CIFS_STATS2 is not set
> CONFIG_CIFS_WEAK_PW_HASH=y
> CONFIG_CIFS_UPCALL=y
> CONFIG_CIFS_XATTR=y
> CONFIG_CIFS_POSIX=y
> CONFIG_CIFS_ACL=y
> CONFIG_CIFS_DEBUG=y
> # CONFIG_CIFS_DEBUG2 is not set
> CONFIG_CIFS_DFS_UPCALL=y
> CONFIG_CIFS_SMB2=y
> CONFIG_CIFS_FSCACHE=y
> 
> 
> Thank you in advance and best regards
> 
> Tobias Doerffel
> 
> 
> --
> Dipl.-Inf. Tobias Doerffel
> 
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