[PATCH v5 2/9] xfs: add a flag to convert unwritten extents without allocating blocks

[Daejun Park via B4 Relay]

From: Daejun Park <daejun7.park@xxxxxxxxxxx>

xfs_bmapi_write() with XFS_BMAPI_CONVERT also allocates blocks for
holes and delalloc extents in the range. Add XFS_BMAPI_CONVERT_ONLY for
callers that may only convert already allocated blocks. It stops at a
hole or delalloc extent, and returns -ENOSR if it stops before mapping
anything.

Marked for stable because "xfs: refuse a pNFS LAYOUTCOMMIT of a range
without blocks" needs it.

Suggested-by: Christoph Hellwig <hch@xxxxxx>
Link: https://lore.kernel.org/r/20261013120359.GB2944@xxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Daejun Park <daejun7.park@xxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 fs/xfs/libxfs/xfs_bmap.c | 14 ++++++++++++--
 fs/xfs/libxfs/xfs_bmap.h | 10 +++++++++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index ca49bf4a50..050522c58b 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4130,6 +4130,8 @@ xfs_bmapi_finish(
  * Returns a negative error code on failure, including -ENOSPC when it could not
  * allocate any blocks and -ENOSR when it did allocate blocks to convert a
  * delalloc range, but those blocks were before the passed in range.
+ * With XFS_BMAPI_CONVERT_ONLY, it stops at a hole or a delalloc extent instead
+ * of allocating blocks, and returns -ENOSR if it stops before mapping anything.
  */
 int
 xfs_bmapi_write(
@@ -4189,6 +4191,8 @@ xfs_bmapi_write(
 	 */
 	ASSERT((flags & (XFS_BMAPI_PREALLOC | XFS_BMAPI_ZERO)) !=
 			(XFS_BMAPI_PREALLOC | XFS_BMAPI_ZERO));
+	ASSERT(!(flags & XFS_BMAPI_CONVERT_ONLY) ||
+	       (flags & XFS_BMAPI_CONVERT));
 
 	if (XFS_IS_CORRUPT(mp, !xfs_ifork_has_extents(ifp)) ||
 	    XFS_TEST_ERROR(mp, XFS_ERRTAG_BMAPIFORMAT)) {
@@ -4237,6 +4241,9 @@ xfs_bmapi_write(
 		 * that we found, if any.
 		 */
 		if (need_alloc || wasdelay) {
+			if (flags & XFS_BMAPI_CONVERT_ONLY)
+				break;
+
 			bma.eof = eof;
 			bma.conv = !!(flags & XFS_BMAPI_CONVERT);
 			bma.wasdel = wasdelay;
@@ -4332,10 +4339,13 @@ xfs_bmapi_write(
 	 *
 	 * To avoid a successful return with *nmap set to 0, return the magic
 	 * -ENOSR error code for this particular case so that the caller can
-	 * handle it.
+	 * handle it. The same goes for XFS_BMAPI_CONVERT_ONLY stopping at a
+	 * hole or a delalloc extent at the start of the range, in which case
+	 * nothing has been changed.
 	 */
 	if (!n) {
-		ASSERT(bma.nallocs >= *nmap);
+		ASSERT((flags & XFS_BMAPI_CONVERT_ONLY) ? bma.nallocs == 0 :
+							  bma.nallocs >= *nmap);
 		return -ENOSR;
 	}
 	*nmap = n;
diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
index e9f5416e4c..fb7481e819 100644
--- a/fs/xfs/libxfs/xfs_bmap.h
+++ b/fs/xfs/libxfs/xfs_bmap.h
@@ -90,6 +90,13 @@ struct xfs_bmalloca {
 /* Try to align allocations to the extent size hint */
 #define XFS_BMAPI_EXTSZALIGN	(1u << 11)
 
+/*
+ * Use with XFS_BMAPI_CONVERT to convert unwritten extents without allocating
+ * blocks. Stop at a hole or a delalloc extent: return the mappings found so
+ * far, or -ENOSR if there are none.
+ */
+#define XFS_BMAPI_CONVERT_ONLY	(1u << 12)
+
 #define XFS_BMAPI_FLAGS \
 	{ XFS_BMAPI_ENTIRE,	"ENTIRE" }, \
 	{ XFS_BMAPI_METADATA,	"METADATA" }, \
@@ -102,7 +109,8 @@ struct xfs_bmalloca {
 	{ XFS_BMAPI_COWFORK,	"COWFORK" }, \
 	{ XFS_BMAPI_NODISCARD,	"NODISCARD" }, \
 	{ XFS_BMAPI_NORMAP,	"NORMAP" },\
-	{ XFS_BMAPI_EXTSZALIGN,	"EXTSZALIGN" }
+	{ XFS_BMAPI_EXTSZALIGN,	"EXTSZALIGN" }, \
+	{ XFS_BMAPI_CONVERT_ONLY,	"CONVERT_ONLY" }
 
 
 static inline int xfs_bmapi_aflag(int w)

-- 
2.43.0