[PATCH 04/48] xfs: track transaction header decode state explicitly

[Dave Chinner <dgc@kernel.org>]

xlog_recovery_process_trans() decides whether an incoming op record is (a
fragment of) the transaction header or a log item region by checking whether
the transaction's item queue is empty. That is an indirect signal: it
happens to be true only while the header is being assembled because no item
is added until the header is complete.

Replace it with an explicit bool r_hdr_decoded in struct xlog_recover. It is
set once the transaction header has been fully assembled in
xlog_recover_init_new_trans() - the same point at which the placeholder item
is added - and the routing check in xlog_recovery_process_trans() now tests
!r_hdr_decoded instead of list_empty(&trans->r_itemq).

r_hdr_decoded is zero-initialised to false when the transaction is allocated,
so no explicit initialisation is required. No functional change.

Changes:
- Add r_hdr_decoded to struct xlog_recover
- Set it when the transaction header is fully decoded in
  xlog_recover_init_new_trans()
- Use !r_hdr_decoded rather than an empty item queue to detect header ophdrs
  in xlog_recovery_process_trans()

Created-by-AI: Claude Opus 4.8 (1M context)

Prompt: The addition of r_hdr_decoded to replace the list_empty() check is
the second patch. [Refactor patch 2 of 4.]
---
 fs/xfs/libxfs/xfs_log_recover.h |  1 +
 fs/xfs/xfs_log_recover.c        | 24 ++++++++++++++----------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_log_recover.h b/fs/xfs/libxfs/xfs_log_recover.h
index 9e712e62369c..ad73a1a6abf8 100644
--- a/fs/xfs/libxfs/xfs_log_recover.h
+++ b/fs/xfs/libxfs/xfs_log_recover.h
@@ -115,6 +115,7 @@ struct xlog_recover {
 	int			r_state;	/* not needed */
 	xfs_lsn_t		r_lsn;		/* xact lsn */
 	struct list_head	r_itemq;	/* q for items */
+	bool			r_hdr_decoded;	/* trans header fully decoded */
 };
 
 #define ITEM_TYPE(i)	(*(unsigned short *)(i)->ri_buf[0].iov_base)
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index b3e35df7a91b..d5d19769c217 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2155,15 +2155,19 @@ xlog_recover_init_new_trans(
 				sizeof(struct xfs_trans_header) - len;
 	}
 
+	memcpy(ptr, dp, len);
+
 	/*
-	 * Add an item to the transaction once the header is complete: for an
-	 * unsplit header that is this initial fragment (len == full header),
+	 * The header is complete once the full struct has been assembled: for
+	 * an unsplit header that is this initial fragment (len == full header),
 	 * and for a split header it is the continuation fragment that finishes
-	 * it.
+	 * it. Mark it decoded and add the item that subsequent log item regions
+	 * will be decoded into.
 	 */
-	if (cont || len == sizeof(struct xfs_trans_header))
+	if (cont || len == sizeof(struct xfs_trans_header)) {
+		trans->r_hdr_decoded = true;
 		xlog_recover_add_item(&trans->r_itemq);
-	memcpy(ptr, dp, len);
+	}
 	return 0;
 }
 
@@ -2319,14 +2323,14 @@ xlog_recovery_process_trans(
 		flags &= ~XLOG_CONTINUE_TRANS;
 
 	/*
-	 * An empty item queue means we are still decoding the transaction
-	 * header at the start of the transaction rather than a log item. The
-	 * header can arrive whole (flags == 0), as an initial fragment
-	 * (XLOG_CONTINUE_TRANS) or as a continuation fragment
+	 * Until the transaction header has been fully decoded we are still
+	 * assembling it at the start of the transaction rather than decoding a
+	 * log item. The header can arrive whole (flags == 0), as an initial
+	 * fragment (XLOG_CONTINUE_TRANS) or as a continuation fragment
 	 * (XLOG_WAS_CONT_TRANS); XLOG_WAS_CONT_TRANS distinguishes the
 	 * continuation.
 	 */
-	if (list_empty(&trans->r_itemq) &&
+	if (!trans->r_hdr_decoded &&
 	    (!flags || (flags & (XLOG_CONTINUE_TRANS | XLOG_WAS_CONT_TRANS)))) {
 		error = xlog_recover_init_new_trans(log, trans, dp, len,
 					flags & XLOG_WAS_CONT_TRANS);
-- 
2.55.0