Re: [RFC][PATCH] ensure i_ino uniqueness in filesystems without permanent inode numbers (via lazy hashing)

[Jeff Layton <jlayton@poochiereds.net>]

Jeff Layton wrote:
> Here is a different approach to the problem of i_ino uniqueness. Again,
> I'll refer to my original email and patch for a description of the 
> problem...
> 
> With this patch, I'm taking the approach of only assigning out an i_ino
> value when it's actually needed. This adds a lazy_getattr function. If
> i_ino is 0, then this does an iunique and hashes the inode before doing
> the actual getattr.
> 

Actually, after having a closer look at this, I don't think this turns 
out to be feasible either. Some filesystems (including pipefs) want an 
i_ino value early on for generating the qstr passed to d_alloc.

Since they want the value so early, there would be little benefit in 
attempting to delay assigning an i_ino value. It might be a win for some 
filesystems, but ones like pipefs and sockfs wouldn't be able to use 
this scheme, and those are the ones we're primarily concerned with 
performance-wise.

I'm going to plan to clean up my IDR patch and resubmit it, as I think 
it's probably the best scheme we have that seems to actually fix the 
problem.

Unless someone else has a better idea... :-)

-- Jeff