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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 3 Mar 2011 10:17:32 -0800
Message-ID: <AANLkTi=z0gHbrGPUZ+vvNPGrOzGowBuWjMUEZpqS+ZCc@mail.gmail.com>
Subject: Re: [PATCH] Syscalls: reboot: Add options to the reboot syscall to
 remount filesystems ro
To: Ken Sumrall <ksumrall@android.com>
Cc: linux-kernel@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        Jens Axboe <axboe@kernel.dk>, Matthew Wilcox <matthew@wil.cx>,
        Eric Paris <eparis@redhat.com>, Dave Young <hidave.darkstar@gmail.com>,
        Jiri Slaby <jslaby@suse.cz>, James Morris <jmorris@namei.org>,
        linux-fsdevel@vger.kernel.org
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On Thu, Mar 3, 2011 at 9:45 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> How many mounted filesystems do you have that it's so hard to keep track of?

Btw, /proc/mounts will track them for you even if you don't have a
'mount' binary that does.

Parsing that is pretty trivial. If you have spaces or special
characters in your pathnames (you may control the mount paths, you may
not - I have no idea), you'll need to be able to handle the escape
format (\oct). But other than that, it's literally just

 - read all of /proc/mounts into a buffer

 - for each line, split by space, and you'll have the directory name
right there in the second field

 - do the unescaping ("\oct" -> character) if needed. It's good
practice. Test it.

 - just do a read-only remount on it.

All done. No kernel changes necessary. It just works.

                            Linus
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