Re: [RFC PATCH v5 01/19] vfs: export new_inode_pseudo

Jeff Layton
2021-04-08T16:18:08Z

On Wed, 2021-04-07 at 18:08 -0700, Eric Biggers wrote:
> On Fri, Mar 26, 2021 at 01:32:09PM -0400, Jeff Layton wrote:
> > Ceph needs to be able to allocate inodes ahead of a create that might
> > involve a fscrypt-encrypted inode. new_inode() almost fits the bill,
> > but it puts the inode on the sb->s_inodes list and when we go to hash
> > it, that might be done again.
> >
> > We could work around that by setting I_CREATING on the new inode, but
> > that causes ilookup5 to return -ESTALE if something tries to find it
> > before I_NEW is cleared. To work around all of this, just use
> > new_inode_pseudo which doesn't add it to the list.
> >
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
>
> IIRC, this looked like a bug in ilookup5(). Did you come to the conclusion that
> it's not actually a bug?
>

Yes. Al pointed out that it's desirable behavior for most (simpler)
filesystems.

Basically, nothing should have presented the filehandle for this inode
to a client until after I_NEW has been cleared. So, any attempt to look
it up should give you back ESTALE at this point.

I'm not married to this approach however. If there's a better way to do
this, then I'm happy to consider it.
--
Jeff Layton <jlayton@kernel.org>