Re: [PATCH] xfs: pass a commit_mode to xfs_trans_commit

[Brian Foster <bfoster@redhat.com>]

On Fri, May 01, 2020 at 12:42:45PM +0200, Christoph Hellwig wrote:
> On Fri, May 01, 2020 at 06:24:03AM -0400, Brian Foster wrote:
> > I recall looking at this when it was first posted and my first reaction
> > was that I didn't really like the interface. I decided to think about it
> > to see if it grew on me and then just lost track (sorry). It's not so
> > much passing a flag to commit as opposed to the flags not directly
> > controlling behavior (i.e., one flag means sync if <something> is true,
> > another flag means sync if <something else> is true, etc.) tends to
> > confuse me. I don't feel terribly strongly about it if others prefer
> > this pattern, but I still find the existing code more readable.
> > 
> > I vaguely recall thinking it might be nice if we could dump this into
> > transaction state to avoid the aforementioned logic warts, but IIRC that
> > might not have been possible for all users of this functionality..
> 
> Moving the flag out of the transaction structure was the main motivation
> for this series - the fact that we need different arguments to
> xfs_trans_commit is just a fallout from that.  The rationale is that
> I found it highly confusing to figure out how and where we set the sync
> flag vs having it obvious in the one place where we commit the
> transaction.
> 

Sorry, I was referring to moving your new [W|DIR]SYNC variants to
somewhere like xfs_trans_res->tr_logflags in the comment above, not the
existing XFS_TRANS_SYNC flag (which I would keep). Regardless, I didn't
think that would work across the board from looking at it before.
Perhaps it would work in some cases..

I agree that the current approach is confusing in that it's not always
clear when to set the sync flag. I disagree that this patch makes it
obvious and in one place because when I see this:

	error = xfs_trans_commit(args->trans, XFS_TRANS_COMMIT_WSYNC);

... it makes me think the flag has an immediate effect (like COMMIT_SYNC
does) and subsequently raises the same questions around the existing
code of when or when not to use which flag in the context of the
individual transaction. *shrug* Just my .02.

Brian