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Date: Fri, 20 Jan 2012 21:34:46 +0100 From: Jan Kara <jack@...e.cz> To: linux-fsdevel@...r.kernel.org Cc: Eric Sandeen <sandeen@...deen.net>, Dave Chinner <dchinner@...hat.com>, Surbhi Palande <csurbhi@...il.com>, Kamal Mostafa <kamal@...onical.com>, Christoph Hellwig <hch@...radead.org>, LKML <linux-kernel@...r.kernel.org>, xfs@....sgi.com, linux-ext4@...r.kernel.org, Valerie Aurora <val@...consulting.com>, Jan Kara <jack@...e.cz> Subject: [PATCH 8/8] vfs: Document s_frozen state through freeze_super From: Valerie Aurora <val@...consulting.com> [kamal@...onical.com: patch restructure] [jack@...e.cz: updated comments to reflect new situation] Signed-off-by: Valerie Aurora <val@...consulting.com> Tested-by: Peter M. Petrakis <peter.petrakis@...onical.com> Signed-off-by: Kamal Mostafa <kamal@...onical.com> Signed-off-by: Jan Kara <jack@...e.cz> --- fs/super.c | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-) diff --git a/fs/super.c b/fs/super.c index 4aaad7e..557a4ef 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1312,6 +1312,24 @@ static void sb_freeze_to_level(struct super_block *sb, int level) * Syncs the super to make sure the filesystem is consistent and calls the fs's * freeze_fs. Subsequent calls to this without first thawing the fs will return * -EBUSY. + * + * During this function, sb->s_frozen goes through these values: + * + * SB_UNFROZEN: File system is normal, all writes progress as usual. + * + * SB_FREEZE_WRITE: The file system is in the process of being frozen. + * New writes should be blocked, we wait for in-progress writes (using + * s_writers[SB_FREEZE_WRITE-1]) and then sync the file system. + * + * SB_FREEZE_TRANS: The file system is frozen. We wait for all metadata writes + * to finish using s_writers[SB_FREEZE_TRANS-1] and after that call ->freeze_fs + * to finish filesystem freezing. After ->freeze_fs is done nothing should be + * dirty and all modifications are blocked until the file system is thawed. + * + * sb->s_frozen is protected by sb->s_umount. Additionally, + * SB_FREEZE_WRITE is only temporarily set during freeze/thaw while + * holding sb->s_umount for writing, so any other callers holding + * sb->s_umount will never see this state. */ int freeze_super(struct super_block *sb) { -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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