set_super_anon in fs/super.c

[Abhijit Chandrakant Pawar]

Hi Rohan,

On Tue, 2012-10-23 at 18:47 +0530, Rohan Puri wrote:

> 
> 
> On Tue, Oct 23, 2012 at 6:33 PM, Abhijit Chandrakant Pawar
> <abhi.c.pawar at gmail.com> wrote:
> 
>         I am working on the layered file systems. I came across a
>         function called set_super_anon. 
>         This is a callback to the sget function to compare the
>         superblock . This function accepts two parameters. first is
>         superblock * and second is void *.  If you look at the
>         definition of this function, the void* is never used. 
>         Many filesystem uses this function when they are mounting the
>         superblock. Some pass NULL and some pass actual data.I have
>         looked till 2.6.31 but there isnt any trace of the usage of
>         second parameter. 
>         
>         If it is never used then why its added to the function param
>         list?  Is there any historical reason during the older kernel
>         days? 
>         
>         Regards,
>         Abhijit Pawar 
>         
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>         
> 
> 
> Hi Abhijit,
> 
> See the issue is this function is passed as an argument to sget(), now
> their are many other file-systems that defined their own set_super
> function & for that they need data argument where they usually pass
> mount-related data
> 
> For eg. see the definition and usage of function nfs_set_super(). 
> 
> So, the prototype of the sget() should contain function ptr
> (set_super()) and this function ptr should have data argument also.
> Now one usage can imply NO USE of the data parameter, which is
> set_super_anon, but other file-systems may require, so the sget()
> prototype should be generic to support, both the cases.
> 

Yes... thats what I thought.   many are passing data un-necessarily to
this function wherein they already have captured the required
information for their purpose in their own defined function. 

Wouldnt that cause stack to store the value un-necessarily? It would be
good if everybody passes NULL as second param.


> - Rohan
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