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

Dave Chinner
2014-08-26T22:34:27Z

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@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@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@fromorbit.com