[PATCH 2/5] fs: add STATX_DIO_READ_ALIGN

Christoph Hellwig
2025-01-08T08:56:05Z

Add a separate dio read align field, as many out of place write
file systems can easily do reads aligned to the device sector size,
but require bigger alignment for writes.

This is usually papered over by falling back to buffered I/O for smaller
writes and doing read-modify-write cycles, but performance for this
sucks, so applications benefit from knowing the actual write alignment.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
fs/stat.c | 1 +
include/linux/stat.h | 1 +
include/uapi/linux/stat.h | 4 +++-
3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/stat.c b/fs/stat.c
index 0870e969a8a0..2c0e111a098a 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -725,6 +725,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
tmp.stx_mnt_id = stat->mnt_id;
tmp.stx_dio_mem_align = stat->dio_mem_align;
tmp.stx_dio_offset_align = stat->dio_offset_align;
+ tmp.stx_dio_read_offset_align = stat->dio_read_offset_align;
tmp.stx_subvol = stat->subvol;
tmp.stx_atomic_write_unit_min = stat->atomic_write_unit_min;
tmp.stx_atomic_write_unit_max = stat->atomic_write_unit_max;
diff --git a/include/linux/stat.h b/include/linux/stat.h
index 3d900c86981c..9d8382e23a9c 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -52,6 +52,7 @@ struct kstat {
u64 mnt_id;
u32 dio_mem_align;
u32 dio_offset_align;
+ u32 dio_read_offset_align;
u64 change_cookie;
u64 subvol;
u32 atomic_write_unit_min;
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 8b35d7d511a2..f78ee3670dd5 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -179,7 +179,8 @@ struct statx {
/* Max atomic write segment count */
__u32 stx_atomic_write_segments_max;

- __u32 __spare1[1];
+ /* File offset alignment for direct I/O reads */
+ __u32 stx_dio_read_offset_align;

/* 0xb8 */
__u64 __spare3[9]; /* Spare space for future expansion */
@@ -213,6 +214,7 @@ struct statx {
#define STATX_MNT_ID_UNIQUE 0x00004000U /* Want/got extended stx_mount_id */
#define STATX_SUBVOL 0x00008000U /* Want/got stx_subvol */
#define STATX_WRITE_ATOMIC 0x00010000U /* Want/got atomic_write_* fields */
+#define STATX_DIO_READ_ALIGN 0x00020000U /* Want/got dio read alignment info */

#define STATX__RESERVED 0x80000000U /* Reserved for future struct statx expansion */

--
2.45.2