[PATCH] Add explanation of I_DIRTY_DATASYNC bit

[PATCH] Add explanation of I_DIRTY_DATASYNC bit

[Jan Kara]

Add explanation of I_DIRTY_DATASYNC bit.

Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 56bd421..475125e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1280,7 +1280,10 @@ struct super_operations {
  * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
  *
  * I_DIRTY_SYNC		Inode itself is dirty.
- * I_DIRTY_DATASYNC	Data-related inode changes pending
+ * 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.
  * I_DIRTY_PAGES	Inode has dirty pages.  Inode itself may be clean.
  * I_NEW		get_new_inode() sets i_state to I_LOCK|I_NEW.  Both
  *			are cleared by unlock_new_inode(), called from iget().
@@ -1312,8 +1315,6 @@ struct super_operations {
  *			purpose reduces latency and prevents some filesystem-
  *			specific deadlocks.
  *
- * Q: Why does I_DIRTY_DATASYNC exist?  It appears as if it could be replaced
- *    by (I_DIRTY_SYNC|I_DIRTY_PAGES).
  * Q: What is the difference between I_WILL_FREE and I_FREEING?
  * Q: igrab() only checks on (I_FREEING|I_WILL_FREE).  Should it also check on
  *    I_CLEAR?  If not, why?

Re: [PATCH] Add explanation of I_DIRTY_DATASYNC bit

[Andreas Schwab]

Jan Kara <jack@suse.cz> writes:

> Add explanation of I_DIRTY_DATASYNC bit.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 56bd421..475125e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1280,7 +1280,10 @@ struct super_operations {
>   * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
>   *
>   * I_DIRTY_SYNC		Inode itself is dirty.
> - * I_DIRTY_DATASYNC	Data-related inode changes pending
> + * I_DIRTY_DATASYNC	Data-related inode changes pending. We keep track of
> + *		`	these changes separately from I_DIRTY_SYNC so that we
                ^

Looks like a typo.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: [PATCH] Add explanation of I_DIRTY_DATASYNC bit

[Jan Kara]

On Wed 06-02-08 17:35:39, Andreas Schwab wrote:
> Jan Kara <jack@suse.cz> writes:
> 
> > Add explanation of I_DIRTY_DATASYNC bit.
> >
> > Signed-off-by: Jan Kara <jack@suse.cz>
> >
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 56bd421..475125e 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1280,7 +1280,10 @@ struct super_operations {
> >   * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
> >   *
> >   * I_DIRTY_SYNC		Inode itself is dirty.
> > - * I_DIRTY_DATASYNC	Data-related inode changes pending
> > + * I_DIRTY_DATASYNC	Data-related inode changes pending. We keep track of
> > + *		`	these changes separately from I_DIRTY_SYNC so that we
>                 ^
> 
> Looks like a typo.
  Oh, OK. Thanks for spotting this. Just next to tab ;). I'll resend a
patch without the typo.

										Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

[PATCH] Add explanation of I_DIRTY_DATASYNC bit

[Jan Kara]

Add explanation of I_DIRTY_DATASYNC bit.

Signed-off-by: Jan Kara <jack@suse.cz>

---
Fixed a typo...

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 56bd421..475125e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1280,7 +1280,10 @@ struct super_operations {
  * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
  *
  * I_DIRTY_SYNC		Inode itself is dirty.
- * I_DIRTY_DATASYNC	Data-related inode changes pending
+ * 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.
  * I_DIRTY_PAGES	Inode has dirty pages.  Inode itself may be clean.
  * I_NEW		get_new_inode() sets i_state to I_LOCK|I_NEW.  Both
  *			are cleared by unlock_new_inode(), called from iget().
@@ -1312,8 +1315,6 @@ struct super_operations {
  *			purpose reduces latency and prevents some filesystem-
  *			specific deadlocks.
  *
- * Q: Why does I_DIRTY_DATASYNC exist?  It appears as if it could be replaced
- *    by (I_DIRTY_SYNC|I_DIRTY_PAGES).
  * Q: What is the difference between I_WILL_FREE and I_FREEING?
  * Q: igrab() only checks on (I_FREEING|I_WILL_FREE).  Should it also check on
  *    I_CLEAR?  If not, why?