[OpenAFS] open/free imbalance

[Marc Dionne]

On Mon, Nov 23, 2009 at 12:49 PM, Simon Wilkinson <sxw@inf.ed.ac.uk> wrote:
>
> Sadly, from a look at the Fedora CVS, it seems like Fedora 12 is shipping
> with IMA enabled.

Yeah I saw the log of the discussion on jabber.  Ick.  Seems odd and
error-prone that dentry_open would not be symmetric with fput in that
respect - like you mentioned on jabber there are places in the kernel
itself that don't deal correctly.

> By the looks of things, we could change to using filp_open with pathnames to
> open and close cache files (in the same way as we currently do on Mac OS X
> and Solaris). However, filp_open doesn't have the support that dentry_open()
> has for opening files with a specific set of credentials. This means that
> the problems we had recently with Apparmour and Selinux crashing us will
> reappear.

I'm pretty sure that we could use override_creds()/revert_creds()
there to get the same effect.

As for the open with a path, that was actually in the tree for a short
while (see commit cadbebc2e50aedea01475620a3add4c315c13faa), with a
lookup + dentry_open that would be easy to replace with filp_open.
>From what I remember testing, it was OK with basic cache filesystems
like ext2/3 but would oops pretty easily with anything more exotic
(xfs, reiser) - locking issues I assumed.  So if we do that we might
lose the cache filesystem flexibility that we gained with the file
handle code.

Marc