Re: [PATCH blktests] create a test for direct io offsets

[Keith Busch <kbusch@kernel.org>]

On Mon, Oct 20, 2025 at 10:28:09PM -0700, Christoph Hellwig wrote:
> seems like a huge win.  Any chance you could try to get this done ASAP
> so that we could make the interface fully discoverable before 6.18 is
> released?

I just want to make sure I am aligned to what you have in mind. Is this
something like this what you're looking for? This reports the kernel's
ability to handle a dio with memory that is discontiguous for a single
device "sector", and reports the virtual gap requirements.

---
diff --git a/block/bdev.c b/block/bdev.c
index 810707cca9703..5881edc3bf928 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1330,6 +1330,12 @@ void bdev_statx(const struct path *path, struct kstat *stat, u32 request_mask)
 		stat->result_mask |= STATX_DIOALIGN;
 	}
 
+	if (request_mask & STATX_DIO_VIRT_SPLIT) {
+		stat->dio_virt_boundary_mask = queue_virt_boundary(
+								bdev->bd_queue);
+		stat->result_mask |= STATX_DIO_VIRT_SPLIT;
+	}
+
 	if (request_mask & STATX_WRITE_ATOMIC && bdev_can_atomic_write(bdev)) {
 		struct request_queue *bd_queue = bdev->bd_queue;
 
@@ -1339,6 +1345,10 @@ void bdev_statx(const struct path *path, struct kstat *stat, u32 request_mask)
 			0);
 	}
 
+	if (bdev_max_segments(bdev) > 1)
+		stat->attributes |= STATX_ATTR_DIO_VEC_SPLIT;
+	stat->attributes_mask |= STATX_ATTR_DIO_VEC_SPLIT;
+
 	stat->blksize = bdev_io_min(bdev);
 
 	blkdev_put_no_open(bdev);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e99306a8f47ce..aec3ed6356aa8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -6105,6 +6105,13 @@ int ext4_getattr(struct mnt_idmap *idmap, const struct path *path,
 		}
 	}
 
+	if (request_mask & STATX_DIO_VIRT_SPLIT) {
+		struct block_device *bdev = inode->i_sb->s_bdev;
+
+		stat->dio_virt_boundary_mask = queue_virt_boundary(bdev->bd_queue);
+		stat->result_mask |= STATX_DIO_VIRT_SPLIT;
+	}
+
 	if ((request_mask & STATX_WRITE_ATOMIC) && S_ISREG(inode->i_mode)) {
 		struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 		unsigned int awu_min = 0, awu_max = 0;
diff --git a/fs/stat.c b/fs/stat.c
index 6c79661e1b961..7f0e12b3b82e8 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -738,6 +738,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
 	tmp.stx_dev_minor = MINOR(stat->dev);
 	tmp.stx_mnt_id = stat->mnt_id;
 	tmp.stx_dio_mem_align = stat->dio_mem_align;
+	tmp.stx_dio_virtual_boundary_mask = stat->dio_virt_boundary_mask;
 	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;
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index caff0125faeac..ce3234d1f9377 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -599,6 +599,18 @@ xfs_report_dioalign(
 		stat->dio_offset_align = stat->dio_read_offset_align;
 }
 
+static void
+xfs_report_dio_split(
+	struct xfs_inode	*ip,
+	struct kstat		*stat)
+{
+	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
+	struct block_device	*bdev = target->bt_bdev;
+
+	stat->dio_virt_boundary_mask = queue_virt_boundary(bdev->bd_queue);
+	stat->result_mask |= STATX_DIO_VIRT_SPLIT;
+}
+
 unsigned int
 xfs_get_atomic_write_min(
 	struct xfs_inode	*ip)
@@ -743,6 +755,8 @@ xfs_vn_getattr(
 			xfs_report_dioalign(ip, stat);
 		if (request_mask & STATX_WRITE_ATOMIC)
 			xfs_report_atomic_write(ip, stat);
+		if (request_mask & STATX_DIO_VIRT_SPLIT)
+			xfs_report_dio_split(ip, stat);
 		fallthrough;
 	default:
 		stat->blksize = xfs_stat_blksize(ip);
diff --git a/include/linux/stat.h b/include/linux/stat.h
index e3d00e7bb26d9..57088eedb6f92 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -55,6 +55,7 @@ struct kstat {
 	u32		dio_mem_align;
 	u32		dio_offset_align;
 	u32		dio_read_offset_align;
+	u32		dio_virt_boundary_mask;
 	u32		atomic_write_unit_min;
 	u32		atomic_write_unit_max;
 	u32		atomic_write_unit_max_opt;
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 1686861aae20a..3f79359cf7154 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -184,7 +184,9 @@ struct statx {
 
 	/* Optimised max atomic write unit in bytes */
 	__u32	stx_atomic_write_unit_max_opt;
-	__u32	__spare2[1];
+
+	/* Virtual boundary mask between io vectors that require a split */
+	__u32	stx_dio_virtual_boundary_mask;
 
 	/* 0xc0 */
 	__u64	__spare3[8];	/* Spare space for future expansion */
@@ -219,6 +221,7 @@ struct statx {
 #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_DIO_VIRT_SPLIT	0x00040000U	/* Want/got dio virtual boundary split */
 
 #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
 
@@ -255,6 +258,7 @@ struct statx {
 #define STATX_ATTR_VERITY		0x00100000 /* [I] Verity protected file */
 #define STATX_ATTR_DAX			0x00200000 /* File is currently in DAX state */
 #define STATX_ATTR_WRITE_ATOMIC		0x00400000 /* File supports atomic write operations */
+#define STATX_ATTR_DIO_VEC_SPLIT	0x00800000 /* File supports vector crossing dio payloads */
 
 
 #endif /* _UAPI_LINUX_STAT_H */
--