linux-kernel - Re: [PATCH 14/39] ovl: stack file ops

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Message-ID: <CAJfpegsnvxUNCaE4c1_UDKq169i8WBTMuWzyvyo8UvenqZCUXg@mail.gmail.com>
Date:   Wed, 13 Jun 2018 11:21:30 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 14/39] ovl: stack file ops

On Tue, Jun 12, 2018 at 8:31 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Tue, Jun 12, 2018 at 07:24:23PM +0100, Al Viro wrote:

>> I hate it, but... consider path_open() objections withdrawn for now.

Is that an ACK for the pull if I follow up with fixes for mmap botch, etc?

>> Uses of ->vm_file (and rules for those) are too convoluted to untangle
>> at the moment.  I still would love to get that straightened out, but
>> it's not this cycle fodder, more's the pity...

Looked at some other options...  What coda mmap does looks very
dubious.  It only sets f_mapping, not vm_file.  That's going to get
into all sorts of trouble when underlying fs tries to look at
file_inode() or worse, ->private_data.  Looks like that should be
converted to what overlayfs does, to have a remote chance of actually
not crashing on most filesystems.  Does anybody actually use coda
still?

> PS: conversion of ->f_path.dentry is easy and that can probably go this
> cycle - it's a fairly trivial change, with no functional changes unless
> overlayfs is used with <filesystem>, fixing really bad shit if it ever
> gets used thus.  I'm not asking to put that into overlayfs pull *and*
> it's independent from the "want to kill that fucking kludge" stuff.
> The latter is too hard for this cycle, unfortunately.

So this is about adding a file_dentry_check() (or whatever we want to
call it) helper to be used by all filesystems when dereferecing
f_path.dentry, right?

Thanks,
Miklos