Re: [PATCH 1/9] seek_sanity_test: fix allocation unit detection on XFS realtime

["Darrick J. Wong" <djwong@kernel.org>]

Does this patch fix NFS for you?

--D
---
From: Darrick J. Wong <djwong@kernel.org>

seek_sanity_test: use XFS ioctls to determine file allocation unit size

liuyd.fnst@fujitsu.com reported that my recent change to the seek sanity
test broke NFS.  I foolishly thought that st_blksize was sufficient to
find the file allocation unit size so that applications could figure out
the SEEK_HOLE granularity.  Replace that with an explicit callout to XFS
ioctls so that xfs realtime will work again.

Fixes: e861a302 ("seek_sanity_test: fix allocation unit detection on XFS realtime")
Reported-by: liuyd.fnst@fujitsu.com
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 src/Makefile           |    4 ++++
 src/seek_sanity_test.c |   40 +++++++++++++++++++++++++++++++---------
 2 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/src/Makefile b/src/Makefile
index 38628a22..b89a7a5e 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -82,6 +82,10 @@ ifeq ($(HAVE_LIBCAP), true)
 LLDLIBS += -lcap
 endif
 
+ifeq ($(HAVE_FSXATTR_XFLAG_HASATTR), yes)
+LCFLAGS += -DHAVE_FSXATTR_XFLAG_HASATTR
+endif
+
 ifeq ($(HAVE_SEEK_DATA), yes)
  ifeq ($(HAVE_FSXATTR_XFLAG_HASATTR), yes)
   ifeq ($(HAVE_NFTW), yes)
diff --git a/src/seek_sanity_test.c b/src/seek_sanity_test.c
index 1030d0c5..b53f4862 100644
--- a/src/seek_sanity_test.c
+++ b/src/seek_sanity_test.c
@@ -40,6 +40,32 @@ static void get_file_system(int fd)
 	}
 }
 
+#ifdef HAVE_FSXATTR_XFLAG_HASATTR
+/* Compute the file allocation unit size for an XFS file. */
+static int detect_xfs_alloc_unit(int fd)
+{
+	struct fsxattr fsx;
+	struct xfs_fsop_geom fsgeom;
+	int ret;
+
+	ret = ioctl(fd, XFS_IOC_FSGEOMETRY, &fsgeom);
+	if (ret)
+		return -1;
+
+	ret = ioctl(fd, FS_IOC_FSGETXATTR, &fsx);
+	if (ret)
+		return -1;
+
+	alloc_size = fsgeom.blocksize;
+	if (fsx.fsx_xflags & FS_XFLAG_REALTIME)
+		alloc_size *= fsgeom.rtextsize;
+
+	return 0;
+}
+#else
+# define detect_xfs_alloc_unit(fd) (-1)
+#endif
+
 static int get_io_sizes(int fd)
 {
 	off_t pos = 0, offset = 1;
@@ -47,6 +73,10 @@ static int get_io_sizes(int fd)
 	int shift, ret;
 	int pagesz = sysconf(_SC_PAGE_SIZE);
 
+	ret = detect_xfs_alloc_unit(fd);
+	if (!ret)
+		goto done;
+
 	ret = fstat(fd, &buf);
 	if (ret) {
 		fprintf(stderr, "  ERROR %d: Failed to find io blocksize\n",
@@ -54,16 +84,8 @@ static int get_io_sizes(int fd)
 		return ret;
 	}
 
-	/*
-	 * st_blksize is typically also the allocation size.  However, XFS
-	 * rounds this up to the page size, so if the stat blocksize is exactly
-	 * one page, use this iterative algorithm to see if SEEK_DATA will hint
-	 * at a more precise answer based on the filesystem's (pre)allocation
-	 * decisions.
-	 */
+	/* st_blksize is typically also the allocation size */
 	alloc_size = buf.st_blksize;
-	if (alloc_size != pagesz)
-		goto done;
 
 	/* try to discover the actual alloc size */
 	while (pos == 0 && offset < alloc_size) {