Re: [RFC][PATCH 0/5] NFS: trace points added to mounting path

[Greg Banks <gnb at melbourne dot sgi dot com>]

J. Bruce Fields wrote:
> On Fri, Jan 23, 2009 at 09:54:20AM +1100, Greg Banks wrote:
>   
>> J. Bruce Fields wrote:
>>     
>>> On Thu, Jan 22, 2009 at 10:59:49AM -0500, Steve Dickson wrote:
>>>   
>>>       
>>>> J. Bruce Fields wrote:
>>>>     
>>>>
>>>> Interesting.... Store something like a reason code (similar to what they have
>>>> in he Kerberos)
>>>>     
>>>>         
>>> Maybe.
>>>
>>>   
>>>       
>>>> in somewhere in the proc file system? 
>>>>     
>>>>         
>>> But then I don't know how you'd associate it with a particular mount
>>> attempt.
>>>
>>>
>>>   
>>>       
>> You could do something truly awful like add a new code in the unused
>> bits of the errno value returned from mount.  It would confuse an
>> unmodified userspace, but reporting "Unknown Error" isn't much less
>> useful than "I/O Error".
>>     
>
> There must be cases where the existing error gives us some information,
> but not as much as we'd like, so the "Unknown Error" could be a step
> backwards for unmodified userspace.  An extra mount option (normally
> hidden from the user) could be used to tell the kernel that the
> application doing the mount was capable of handling the new error codes.
> Ugh.
>
>
>   
Ugh is right.

On further thought, you could use the extra mount option to enable a
behaviour where the kernel would format into the mount options buffer a
string describing the reasons for the mount failure.  If the option
weren't present the kernel could emit that same message via printk().

-- 
Greg Banks, P.Engineer, SGI Australian Software Group.
the brightly coloured sporks of revolution.
I don't speak for SGI.