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 17:52:49 +0200
From:	Phil Carmody <ext-phil.2.carmody@...ia.com>
To:	ext 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 <e@...da02.nokia.com>
Subject: Re: [PATCH] Syscalls: reboot: Add options to the reboot syscall to
	remount filesystems ro

On 02/03/11 23:31 -0800, ext Ken Sumrall wrote:
> Add 4 new commands to the reboot system call, that do the same thing as the
> RESTART, HALT, POWER_OFF, and RESTART2 commands, but also remount writable
> filesystems as read-only just before doing what the command normally does.
> Now that Android is using EXT4, and since we don't have a standard init
> setup to unmount filesystems before rebooting, this allows the system to
> reboot with clean filesystems, and also improves boot time as the journal
> does not need to be replayed when mounting the filesystem.
> 
> Signed-off-by: Ken Sumrall <ksumrall@...roid.com>
> ---
...
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 7f5a0cd..3f474e6 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -392,6 +392,9 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  	mutex_lock(&reboot_mutex);
>  	switch (cmd) {
>  	case LINUX_REBOOT_CMD_RESTART:
> +	case LINUX_REBOOT_CMD_RMNT_RESTART:
> +		if (cmd == LINUX_REBOOT_CMD_RMNT_RESTART)
> +			emergency_remount_synchronous();
>  		kernel_restart(NULL);
>  		break;

What happened to fall through cases?

 	switch (cmd) {
+	case LINUX_REBOOT_CMD_RMNT_RESTART:
+		emergency_remount_synchronous();
 	case LINUX_REBOOT_CMD_RESTART:
		kernel_restart(NULL);
 		break;

Ditto for the other related hunks. 

Then again, I agree with the other responders, in particular those about fixing 
problems with init in init itself.

Phil
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