Re: cifs ignores sysct setting

[Suresh Jayaraman <sjayaraman-IBi9RG/b67k@public.gmane.org>]

On 10/10/2011 07:07 PM, Jeff Layton wrote:
> On Mon, 10 Oct 2011 18:36:15 +0530
> Suresh Jayaraman <sjayaraman-IBi9RG/b67k@public.gmane.org> wrote:
> 
>> On 10/10/2011 03:02 PM, Alexander Swen wrote:
>>>
>>> Hi Steve and other CIFS developers, 
>>>
>>> please help me with the following: 
>>> 1. fix the bug I explain below ;-) 
>>> 2. tell me to what bug tracking system I should to file it to. 
>>>
>>> so, imho this is a bug: when I load the cifs module it insists in setting oplockenabled to 1 while we want to have locking disabled (due to our poormen's nas who's performance sinks to subzero when we do serious io ;-) 
>>>
>>> I've filed this bug at Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=644135 
>>>
>>> I paste all details over here as well: 
>>> <paste> 
>>> Package: linux-mage
>>> Version: 2.6.32-5-amd64
>>>
>>> cifs.ko module (which is included in the kernel pkg as far as i know)
>>> cifs driver version 1.61
>>>
>>> when cifs module loads oplock is enabled by default.
>>> so I can do
>>> echo 0 >/proc/fs/cifs/OplockEnabled
>>> but that won't persist through a driver reload. so we tried adding this to /etc/sysctl.conf:
>>> fs.cifs.OplockEnabled = 0
>>> however:
>>>
>>> root@nl14s0008-vm1:~# echo 0 >/proc/fs/cifs/OplockEnabled
>>> root@nl14s0008-vm1:~# cat /proc/fs/cifs/OplockEnabled
>>> 0
>>> root@nl14s0008-vm1:~# modprobe -r cifs
>>> root@nl14s0008-vm1:~# tail -1 /etc/sysctl.conf
>>> fs.cifs.OplockEnabled = 0
>>
>> IIUC, CIFS OplockEnabled is not a proper sysctl, it is just a proc
>> entry. Sysctls are listed below /proc/sys/ directory.
>>
>> For e.g. try
>>    sysctl -w fs.cifs.OplockEnabled=0
>>
>> you'll see the error: "/proc/sys/fs/cifs/OplockEnabled: No such file or
>> directory". Also,
>>
>>    sysctl -p
>>
>> will throw the error: "/proc/sys/fs/cifs/OplockEnabled: No such file or
>> directory"
>>
>> It is not clear to me why do you want to unload and reload cifs module
>> often? The general usage is load module during boot or on first use and
>> the module lives on till the machine goes down.
>>
>> I'm not seeing an justification for making it an module parameter. Could
>> you please explain more on how it will be useful?
>>
> 
> I agree with Alexander on this one...
> 
> Making that a module parm would allow you to set that parameter at boot
> time without needing to add special startup scripts. IMO, all of the
> procfile "switches" under /proc/fs/cifs should be module parms
> instead.

Making it a module parm would mean that it would no longer be possible
to dynamically change OplockEnabled. But, that might be Ok, because it
is quite unusual to change this setting once the module is loaded,
right?. Also, someone won't be able to see what is the current setting.
Again, not a big deal.

> That would also allow us to get rid of some of the special procfile
> handling code for those files as well.
> 

Agreed.

I'll whip up a patch and post it soon.


-Suresh