fs: add STATX_DIO_READ_ALIGN

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>
Link: https://lore.kernel.org/r/20250109083109.1441561-3-hch@lst.de
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/stat.c b/fs/stat.c
index 0870e969a8a0b80eefb8b737262a69d7bf28feec..2c0e111a098a1ec99b93dae6d90ad786da6571ec 100644 (file)
--- 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 3d900c86981c5b0ae92bb4e972ff36586093f59f..9d8382e23a9c69ffaabcde1f0697a4683205fc3e 100644 (file)
--- 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 8b35d7d511a287706ab757695b4d01c3c793ece2..f78ee3670dd5d7c897c42e9a97c1ba70856b18fa 100644 (file)
--- 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 */