linux-kernel - Re: [PATCH] Syscalls: reboot: Add options to the reboot syscall to remount filesystems ro

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Date:	Thu, 3 Mar 2011 10:17:32 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ken Sumrall <ksumrall@...roid.com>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>,
	Matthew Wilcox <matthew@....cx>,
	Eric Paris <eparis@...hat.com>,
	Dave Young <hidave.darkstar@...il.com>,
	Jiri Slaby <jslaby@...e.cz>, James Morris <jmorris@...ei.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] Syscalls: reboot: Add options to the reboot syscall to
 remount filesystems ro

On Thu, Mar 3, 2011 at 9:45 AM, Linus Torvalds
<torvalds@...ux-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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