[PATCH 1/4] xfs: refactor xlog_recover_process_data()

[Dave Chinner]

On Tue, Aug 26, 2014 at 08:41:13AM -0400, Brian Foster wrote:
> On Tue, Aug 26, 2014 at 11:21:38AM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner at redhat.com>
> > 
> > Clean up xlog_recover_process_data() structure in preparation for
> > fixing the allocationa nd freeing context of the transaction being
> > recovered.
> > 
> > Signed-off-by: Dave Chinner <dchinner at redhat.com>
> > ---
> >  fs/xfs/xfs_log_recover.c | 151 ++++++++++++++++++++++++++---------------------
> >  1 file changed, 84 insertions(+), 67 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> > index 01becbb..1970732f 100644
> > --- a/fs/xfs/xfs_log_recover.c
> > +++ b/fs/xfs/xfs_log_recover.c
> > @@ -3531,12 +3531,78 @@ out:
> >  }
> >  
> >  STATIC int
> > -xlog_recover_unmount_trans(
> > -	struct xlog		*log)
> > +xlog_recovery_process_ophdr(
> > +	struct xlog		*log,
> > +	struct hlist_head	rhash[],
> > +	struct xlog_rec_header	*rhead,
> > +	struct xlog_op_header	*ohead,
> > +	xfs_caddr_t		dp,
> > +	xfs_caddr_t		lp,
> > +	int			pass)
> >  {
> > -	/* Do nothing now */
> > -	xfs_warn(log->l_mp, "%s: Unmount LR", __func__);
> > -	return 0;
> > +	struct xlog_recover	*trans;
> > +	xlog_tid_t		tid;
> > +	int			error;
> > +	unsigned long		hash;
> > +	uint			flags;
> > +	unsigned int		hlen;
> > +
> > +	hlen = be32_to_cpu(ohead->oh_len);
> > +	tid = be32_to_cpu(ohead->oh_tid);
> > +	hash = XLOG_RHASH(tid);
> > +	trans = xlog_recover_find_tid(&rhash[hash], tid);
> > +	if (!trans) {
> > +		/* add new tid if this is a new transaction */
> > +		if (ohead->oh_flags & XLOG_START_TRANS) {
> > +			xlog_recover_new_tid(&rhash[hash], tid,
> > +					     be64_to_cpu(rhead->h_lsn));
> > +		}
> > +		return 0;
> > +	}
> > +
> 
> Overall this looks pretty good to me. I wonder if we can clean this up
> to separate state management from error detection while we're at it. I
> don't see any reason this code to find trans has to be up here.
> 
> > +	error = -EIO;
> > +	if (dp + hlen > lp) {
> > +		xfs_warn(log->l_mp, "%s: bad length 0x%x", __func__, hlen);
> > +		WARN_ON(1);
> > +		goto out_free;
> > +	}
> > +
> > +	flags = ohead->oh_flags & ~XLOG_END_TRANS;
> > +	if (flags & XLOG_WAS_CONT_TRANS)
> > +		flags &= ~XLOG_CONTINUE_TRANS;
> > +
> 
> 	/* we should find a trans for anything other than a start op */
> 	trans = xlog_recover_find_tid(&rhash[hash], tid);
> 	if (((ohead->oh_flags & XLOG_START_TRANS) && trans) ||
> 	    (!(ohead->oh_flags & XLOG_START_TRANS) && !trans)) {
> 		xfs_warn(log->l_mp, "%s: bad transaction 0x%x oh_flags 0x%x trans %p",
> 			 __func__, tid, ohead->oh_flags, trans);
> 		ASSERT(0);
> 		return -EIO;
> 	}
> 
> Maybe returning error here is not the right thing to do because we want
> the recovery to proceed. We could still dump a warning and return 0
> though.

Urk. Try understanding why that logic exists in a couple of years
time when you've forgetten all the context. :/

> > +	switch (flags) {
> > +	/* expected flag values */
> > +	case 0:
> > +	case XLOG_CONTINUE_TRANS:
> > +		error = xlog_recover_add_to_trans(log, trans, dp, hlen);
> > +		break;
> > +	case XLOG_WAS_CONT_TRANS:
> > +		error = xlog_recover_add_to_cont_trans(log, trans, dp, hlen);
> > +		break;
> > +	case XLOG_COMMIT_TRANS:
> > +		error = xlog_recover_commit_trans(log, trans, pass);
> > +		break;
> > +
> > +	/* unexpected flag values */
> > +	case XLOG_UNMOUNT_TRANS:
> > +		xfs_warn(log->l_mp, "%s: Unmount LR", __func__);
> > +		error = 0;
> > +		break;
> > +	case XLOG_START_TRANS:
> > +		xfs_warn(log->l_mp, "%s: bad transaction 0x%x", __func__, tid);
> > +		ASSERT(0);
> > +		break;
> 
> 		xlog_recover_new_tid(&rhash[hash], tid, be64_to_cpu(rhead->h_lsn)
> 		error = 0;
> 		break;
> 

I like the idea, but I don't like the suggested implementation. I
was in two minds as to whether I should factor
xlog_recover_find_tid() further.  There's only one caller of it and
only one caller of xlog_recover_new_tid() and the happen within
three lines of each other. Hence I'm thinking that it makes more
sense to wrap the "find or allocate trans" code in a single helper
and lift all that logic clean out of this function. That helper can
handle all the XLOG_START_TRANS logic more cleanly, I think....

Actually, that makes the factoring I've already done a little
inconsistent. Let me rework this a bit.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com