From: Kamal Mostafa Subject: [PATCH v2 6/7] VFS: Document s_frozen state through freeze_super Date: Thu, 8 Dec 2011 10:04:36 -0800 Message-ID: <1323367477-21685-7-git-send-email-kamal@canonical.com> References: <1323367477-21685-1-git-send-email-kamal@canonical.com> Cc: linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Surbhi Palande , Valerie Aurora , Kamal Mostafa , Christopher Chaltain , "Peter M. Petrakis" , Mikulas Patocka To: Jan Kara , Alexander Viro , Andreas Dilger , Matthew Wilcox , Randy Dunlap , Theodore Tso Return-path: In-Reply-To: <1323367477-21685-1-git-send-email-kamal@canonical.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org From: Valerie Aurora BugLink: https://bugs.launchpad.net/bugs/897421 Signed-off-by: Valerie Aurora Cc: Kamal Mostafa Tested-by: Peter M. Petrakis [kamal@canonical.com: patch restructure] Signed-off-by: Kamal Mostafa --- fs/super.c | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-) diff --git a/fs/super.c b/fs/super.c index 5629d06..a56696b 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1140,6 +1140,24 @@ out: * 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 + * and any remaining out-standing writes are being synced. Writes + * that complete in-process writes should be permitted but new ones + * should be blocked. + * + * SB_FREEZE_TRANS: The file system is frozen. The ->freeze_fs and + * ->unfreeze_fs ops are the only operations permitted to write to the + * file system in this state. + * + * 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) { -- 1.7.5.4