linux-kernel - Re: [PATCH] x86: defconfig: Enable CONFIG

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Message-ID: <20141201035426.GK9561@dastard>
Date:	Mon, 1 Dec 2014 14:54:26 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Lennart Poettering <mzxreary@...inter.de>
Cc:	Richard Weinberger <richard@....at>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org,
	"systemd-devel@...ts.freedesktop.org" 
	<systemd-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] x86: defconfig: Enable CONFIG_FHANDLE

On Mon, Dec 01, 2014 at 02:03:43AM +0100, Lennart Poettering wrote:
> On Mon, 01.12.14 01:41, Richard Weinberger (richard@....at) wrote:
> 
> > CC'ing systemd folks.
> > 
> > Lennart, can you please explain why you need CONFIG_FHANDLE for systemd?
> > Maybe I'm reading the source horrible wrong.
> 
> For two usecases:
> 
> a) Being able to detect if something is a mount point. The traditional
>    way to do this is by stat()ing the dir in question and its parent
>    and comparing st_dev. That logic is not able to detect bind mounts
>    however, if destination and the place the mount is at are actually
>    on the same file system... Thus we check the mount id too, if we
>    can get our hands on it.

So what you really want in the mount id in st_buf.st_dev, not the
underlying device number. i.e. fstatat(dirfd, path, buf,
AT_MOUNTID)?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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