Re: [pnfs] module_init not called in RPM

[Benny Halevy <bhalevy@panasas.com>]

On Jun. 07, 2009, 11:51 +0300, Benny Halevy <bhalevy@panasas.com> wrote:
> On Jun. 04, 2009, 15:31 +0300, Boaz Harrosh <bharrosh@panasas.com> wrote:
>> On 06/04/2009 11:51 AM, Fred Isaman wrote:
>>> People were having problems with the fedora RPMs, and investigation
>>> shows that the problem is related to the fact that  CONFIG_NFS_FS is
>>> set to "m" while CONFIG_PNFS_BLOCK is set to "y".  In this case the
>>> driver never registers (via module_init) with the NFS code.  The
>>> problem is fixed by setting CONFIG_PNFS_BLOCK to "m".
>>>
>>> Is there anyway (simple) way this could be expected to work?  Because
>>> as is, my understanding is that the block-layout tries to register
>>> with (the yet unloaded) NFS module, and once the NFS module is loaded,
>>> the block-layout code is never called again.
>>>
>>> Steve, would it be possible in the meantime to change to "CONFIG_PNFS_BLOCK=m"?
>>>
>>> Benny, does the PANLAYOUT driver have the same problem?
> 
> I believe so. When I try to configure panlayout as 'y' rather than 'm'
> it looks like it does not even link properly with neither the nfs module
> nor the kernel.

FWIW, When both CONFIG_NFS_FS and CONFIG_PNFS_PANLAYOUT are set to 'y'
it does get linked properly with the kernel...

Benny

> 
>>> Fred
>>
>> Below little trick will default the layout driver to be the same as the CONFIG_NFS_FS
>> that is if CONFIG_NFS_FS=y then CONFIG_PNFS_BLOCK will be y and so for =m.
>>
>> config PNFS_OBJLAYOUT
>> 	tristate "Provide a pNFS block client (EXPERIMENTAL)"
>> 	depends on NFS_FS && PNFS
>> 	help
>> 	  Say M or Y here if you want your pNfs client to support the block protocol.
>> 	  Note if CONFIG_NFS_FS==M then this must also be ==M.
>>
>> User can select them apart manually but if CONFIG_NFS_FS changes then CONFIG_PNFS_BLOCK
>> will automatically change also. Only by first changing CONFIG_NFS_FS then manually
>> changing CONFIG_PNFS_BLOCK they can separate. In which case the prompt should warn about
>> CONFIG_NFS_FS=m CONFIG_PNFS_BLOCK=y does not work.
>> (Experiment with this in make xconfig and see)
>>
>> ---
>> This works because Kconfig is not very recursive. the dependency chain figures out that
>> CONFIG_PNFS_BLOCK is eventually dependent on CONFIG_NFS_FS, but the default value is taken
>> from the direct parent which is CONFIG_PNFS, which is "bool", therefor the =Y default.
>> Above though redundant for dependency will select the correct default value dependent
>> on the NFS setting.
>>
>> I'll send a patch upstream
> 
> Thanks!
> Besides a short term work around I think we may want to rethink the way
> layout drivers are being used...
> 
> Today the layout driver registers its layout type and it must be explicitly
> loaded to do that, so you may need to manually modprobe it to get it to work.
> Thereafter, the admin / user has no choice or control when to use on a
> per-filesystem basis.  It's all or nothing.
> 
> I think that a more practical way would be to identify the layout driver
> as a mount option and then dynamically discover and load it at mount time.
> With this mechanism we can also have a default setting for this mount
> option to be layout=auto, in which case, the nfs client will load predefined
> layout drivers it knows about, based on the layout type attribute it sees
> in run time.  layout=none will disable pnfs for this mount.
> 
> Benny
> 
>> Boaz
>>
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