[PATCH 8/8] vfs: Document s_frozen state through freeze_super
From: Jan Kara <jack@suse.cz>
Date: 2012-01-20 20:34:46
Also in:
linux-fsdevel, linux-xfs, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
From: Valerie Aurora <redacted> [kamal@canonical.com: patch restructure] [jack@suse.cz: updated comments to reflect new situation] Signed-off-by: Valerie Aurora <redacted> Tested-by: Peter M. Petrakis <redacted> Signed-off-by: Kamal Mostafa <redacted> Signed-off-by: Jan Kara <jack@suse.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