Re: [fuse-devel] [PATCH 01/25] VFS: move attr_kill logic fromnotify_change into helper function

[Miklos Szeredi]

There's another way to deal with this in NFS and fuse, without having
to change the API:

 - remove suid/sgid bits from i_mode, when refreshing the inode attributes
 - store the removed bits (or the original mode)  in the fs' inode strucure
 - in ->getattr() restore the original mode into the returned stat

This way the VFS believes, that the inode does not in fact have the
suid/sgid bits and so won't call ->setattr() unnecessarily.

I've tested a similar change in fuse for working around unneeded check
for the directory sticky bit.

Yes, this is cheating the interface, but there's a deeper level where
it makes sense: the VFS should not be checking _any_ inode attribute
besides the file type, since they can change at any moment, and the
VFS might be using stale data without having first properly
revalidated it.

Miklos
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