Re: 2.6.0-test6 crash while reading files in /proc/fs/reiserfs/sda1

[viro@parcelfarce.linux.theplanet.co.uk]

On Thu, Oct 02, 2003 at 02:08:26PM +0400, Nikita Danilov wrote:
> What about creating fake struct vfsmount for /proc/fs/reiserfs/<devname>
> and attaching it to the super block of /<mountpoint>? After all
> /proc/fs/reiserfs/<devname> is just a view into /<mountpoint>. This will
> automatically guarantee that /<mountpoint> cannot be unmounted while
> files in /proc/fs/reiserfs/<devname> are opened. Will this screw up
> dcache?

I don't see what it would buy you - you get to revalidate the pointer to
vfsmount instead of revalidating pointer to superblock, which is not easier.
sget()-based revalidation actually works OK - see previous reply for details.
With optimistic sget() (which we should've done a long time ago) it's
actually cheaper than your original "search by dev_t" - you are looking
only through reiserfs superblocks instead of all superblocks in system.
 
> Yes, possible. I had similar problem in reiser4 also: for some seq_file,
> x_start() allocated some data structure (struct x_struct) that is used
> by x_next(), x_show(), and is deallocated in x_stop(). As x_struct is
> per read invocation rather than per file it cannot be stored in seq_file
> itself. I had to resort to returning x_struct from x_start() and passing
> it without change through x_next()'s. Thing actually changed by x_next()
> was embedded in x_struct. Last x_next() had to deallocate x_struct and
> to return NULL (much like your example above).

Umm...  And what's the problem with that?  If your context is created by
->start() and is needed by ->next() and ->stop(), the above is obvious
solution - you are already passing opaque pointer through that sequence,
so that's about as straightforward as it gets...