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From: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>
To: btrfs <linux-btrfs@vger.kernel.org>
Subject: No SysRq remount because sb->s_bdev is NULL
Date: Sat, 28 Jul 2012 15:41:16 +0200
Message-ID: <1389197.DvrDHJORPI@nezir>
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Hi,

During a SysRq emergency remount Btrfs mounts are not remounted. I tracked the 
issue down to this line in do_emergency_remount() in fs/super.c:
if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
	!(sb->s_flags & MS_RDONLY))
s_bdev is NULL for Btrfs super blocks and subsequently do_remount_sb() is 
never called. I couldn't think of a solution, besides resorting to an ugly 
strcmp(sb->s_type->name, "btrfs"), without adding a field to struct super_block 
or similar changes.
Thoughts?

    Flo