[PATCH v3 02/11] fs: correctly document the inode dirty flags

Eric Biggers
2021-01-12T19:05:06Z

The documentation for I_DIRTY_SYNC and I_DIRTY_DATASYNC is a bit
misleading, and I_DIRTY_TIME isn't documented at all. Fix this.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
include/linux/fs.h | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index fd47deea7c176..45a0303b2aeb6 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2084,8 +2084,8 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
/*
* Inode state bits. Protected by inode->i_lock
*
- * Three bits determine the dirty state of the inode, I_DIRTY_SYNC,
- * I_DIRTY_DATASYNC and I_DIRTY_PAGES.
+ * Four bits determine the dirty state of the inode: I_DIRTY_SYNC,
+ * I_DIRTY_DATASYNC, I_DIRTY_PAGES, and I_DIRTY_TIME.
*
* Four bits define the lifetime of an inode. Initially, inodes are I_NEW,
* until that flag is cleared. I_WILL_FREE, I_FREEING and I_CLEAR are set at
@@ -2094,12 +2094,20 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
* Two bits are used for locking and completion notification, I_NEW and I_SYNC.
*
* I_DIRTY_SYNC Inode is dirty, but doesn't have to be written on
- * fdatasync(). i_atime is the usual cause.
- * I_DIRTY_DATASYNC Data-related inode changes pending. We keep track of
+ * fdatasync() (unless I_DIRTY_DATASYNC is also set).
+ * Timestamp updates are the usual cause.
+ * I_DIRTY_DATASYNC Data-related inode changes pending. We keep track of
* these changes separately from I_DIRTY_SYNC so that we
* don't have to write inode on fdatasync() when only
- * mtime has changed in it.
+ * e.g. the timestamps have changed.
* I_DIRTY_PAGES Inode has dirty pages. Inode itself may be clean.
+ * I_DIRTY_TIME The inode itself only has dirty timestamps, and the
+ * lazytime mount option is enabled. We keep track of this
+ * separately from I_DIRTY_SYNC in order to implement
+ * lazytime. This gets cleared if I_DIRTY_INODE
+ * (I_DIRTY_SYNC and/or I_DIRTY_DATASYNC) gets set. I.e.
+ * either I_DIRTY_TIME *or* I_DIRTY_INODE can be set in
+ * i_state, but not both. I_DIRTY_PAGES may still be set.
* I_NEW Serves as both a mutex and completion notification.
* New inodes set I_NEW. If two processes both create
* the same inode, one of them will release its inode and
--
2.30.0