On Tue, Aug 13, 2024 at 09:35:01AM +0200, Christoph Hellwig wrote:
> 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)
min_dio_alignment
> +{
> + 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.
Should we try DIOINFO here as a second to last gasp?
--D
> + */
> + 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
>
>
