Add a new C program to find the minimum direct I/O alignment. This
uses the statx stx_dio_offset_align field if provided, then falls
back to the BLKSSZGET ioctl for block backed file systems and finally
the page size. It is intended as a more capable replacement for the
_min_dio_alignment bash helper.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
src/Makefile | 2 +-
src/min_dio_alignment.c | 66 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 67 insertions(+), 1 deletion(-)
create mode 100644 src/min_dio_alignment.c
diff --git a/src/Makefile b/src/Makefile
index 559209be9..b3da59a0e 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -34,7 +34,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
attr_replace_test swapon mkswap t_attr_corruption t_open_tmpfiles \
fscrypt-crypt-util bulkstat_null_ocount splice-test chprojid_fail \
detached_mounts_propagation ext4_resize t_readdir_3 splice2pipe \
- uuid_ioctl t_snapshot_deleted_subvolume fiemap-fault
+ uuid_ioctl t_snapshot_deleted_subvolume fiemap-fault min_dio_alignment
EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
btrfs_crc32c_forged_name.py popdir.pl popattr.py \
diff --git a/src/min_dio_alignment.c b/src/min_dio_alignment.c
new file mode 100644
index 000000000..c3345bfb2
--- /dev/null
+++ b/src/min_dio_alignment.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2024 Christoph Hellwig
+ */
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/mount.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include "statx.h"
+
+static int min_dio_alignmenent(const char *mntpnt, const char *devname)
+{
+ struct statx stx = { };
+ struct stat st;
+ int fd;
+
+ /*
+ * If the file system supports STATX_DIOALIGN, use the dio_offset_align
+ * member, as that reports exactly the information that we are asking
+ * for.
+ *
+ * STATX_DIOALIGN is only reported on regular files, so use O_TMPFILE
+ * to create one without leaving a trace.
+ */
+ fd = open(mntpnt, O_TMPFILE | O_RDWR | O_EXCL, 0600);
+ if (fd >= 0 &&
+ xfstests_statx(fd, "", AT_EMPTY_PATH, STATX_DIOALIGN, &stx) == 0 &&
+ (stx.stx_mask & STATX_DIOALIGN))
+ return stx.stx_dio_offset_align;
+
+ /*
+ * If we are on a block device and no explicit aligned is reported, use
+ * the logical block size as a guestimate.
+ */
+ if (stat(devname, &st) == 0 && S_ISBLK(st.st_mode)) {
+ int dev_fd = open(devname, O_RDONLY);
+ int logical_block_size;
+
+ if (dev_fd > 0 &&
+ fstat(dev_fd, &st) == 0 &&
+ S_ISBLK(st.st_mode) &&
+ ioctl(dev_fd, BLKSSZGET, &logical_block_size)) {
+ return logical_block_size;
+ }
+ }
+
+ /*
+ * No support for STATX_DIOALIGN and not a block device:
+ * default to PAGE_SIZE.
+ */
+ return getpagesize();
+}
+
+int main(int argc, char **argv)
+{
+ if (argc != 3) {
+ fprintf(stderr, "usage: %s mountpoint devicename\n", argv[0]);
+ exit(1);
+ }
+
+ printf("%d\n", min_dio_alignmenent(argv[1], argv[2]));
+ exit(0);
+}
--
2.43.0
