[PATCH RFC 4/7] fs: Add initial buffered atomic write support info to statx

[John Garry]

Extend statx system call to return additional info for buffered atomic
write support for a file. Currently only direct IO is supported.

New flags STATX_WRITE_ATOMIC_BUF and STATX_ATTR_WRITE_ATOMIC_BUF are for
indicating whether the file knows and supports buffered atomic writes.

Structure statx members stx_atomic_write_unit_{min, max, segments_max} will
be reused for bufferd atomic writes. Flags STATX_WRITE_ATOMIC_DIO and
STATX_WRITE_ATOMIC_BUF are mutually exclusive. With both flags set, neither
fields in statx.result_mask will be set.

For buffered atomic writes, stx_atomic_write_unit_{min, max} must hold the
same value.

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 block/bdev.c              |  3 ++-
 fs/stat.c                 | 26 ++++++++++++++++++--------
 fs/xfs/xfs_iops.c         |  2 +-
 include/linux/fs.h        |  3 ++-
 include/uapi/linux/stat.h |  2 ++
 5 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index e2a9951bd2e9..b80c78aed9f6 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1213,7 +1213,8 @@ void bdev_statx(struct inode *backing_inode, struct kstat *stat,
 
 		generic_fill_statx_atomic_writes(stat,
 			queue_atomic_write_unit_min_bytes(bd_queue),
-			queue_atomic_write_unit_max_bytes(bd_queue));
+			queue_atomic_write_unit_max_bytes(bd_queue),
+			true);
 	}
 
 	blkdev_put_no_open(bdev);
diff --git a/fs/stat.c b/fs/stat.c
index 0c0c4c22c563..cb8283534616 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -94,19 +94,26 @@ EXPORT_SYMBOL(generic_fill_statx_attr);
  * @stat:	Where to fill in the attribute flags
  * @unit_min:	Minimum supported atomic write length in bytes
  * @unit_max:	Maximum supported atomic write length in bytes
+ * @dio:	Whether filling in the fields for direct-IO
  *
- * Fill in the STATX{_ATTR}_WRITE_ATOMIC_DIO flags in the kstat structure
- * from atomic write unit_min and unit_max values.
+ * Fill in the STATX{_ATTR}_WRITE_ATOMIC_{DIO, BUF} flags in the kstat
+ * structure from atomic write unit_min and unit_max values.
  */
 void generic_fill_statx_atomic_writes(struct kstat *stat,
 				      unsigned int unit_min,
-				      unsigned int unit_max)
+				      unsigned int unit_max,
+				      bool dio)
 {
 	/* Confirm that the request type is known */
-	stat->result_mask |= STATX_WRITE_ATOMIC_DIO;
-
-	/* Confirm that the file attribute type is known */
-	stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC_DIO;
+	if (dio) {
+		/* Confirm that the request type is known */
+		stat->result_mask |= STATX_WRITE_ATOMIC_DIO;
+		/* Confirm that the file attribute type is known */
+		stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC_DIO;
+	} else {
+		stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC_BUF;
+		stat->result_mask |= STATX_WRITE_ATOMIC_BUF;
+	}
 
 	if (unit_min) {
 		stat->atomic_write_unit_min = unit_min;
@@ -115,7 +122,10 @@ void generic_fill_statx_atomic_writes(struct kstat *stat,
 		stat->atomic_write_segments_max = 1;
 
 		/* Confirm atomic writes are actually supported */
-		stat->attributes |= STATX_ATTR_WRITE_ATOMIC_DIO;
+		if (dio)
+			stat->attributes |= STATX_ATTR_WRITE_ATOMIC_DIO;
+		else
+			stat->attributes |= STATX_ATTR_WRITE_ATOMIC_BUF;
 	}
 }
 EXPORT_SYMBOL_GPL(generic_fill_statx_atomic_writes);
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 37076176db67..05b20c88ff77 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -655,7 +655,7 @@ xfs_vn_getattr(
 
 			xfs_get_atomic_write_attr(ip, &unit_min, &unit_max);
 			generic_fill_statx_atomic_writes(stat,
-				unit_min, unit_max);
+				unit_min, unit_max, true);
 		}
 		fallthrough;
 	default:
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 08a0b9a4da93..1147d031d5bd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3243,7 +3243,8 @@ void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *);
 void generic_fill_statx_attr(struct inode *inode, struct kstat *stat);
 void generic_fill_statx_atomic_writes(struct kstat *stat,
 				      unsigned int unit_min,
-				      unsigned int unit_max);
+				      unsigned int unit_max,
+				      bool dio);
 extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int);
 extern int vfs_getattr(const struct path *, struct kstat *, u32, unsigned int);
 void __inode_add_bytes(struct inode *inode, loff_t bytes);
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 05f9720d4030..9eef921b3942 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -161,6 +161,7 @@ struct statx {
 #define STATX_DIOALIGN		0x00002000U	/* Want/got direct I/O alignment info */
 #define STATX_MNT_ID_UNIQUE	0x00004000U	/* Want/got extended stx_mount_id */
 #define STATX_WRITE_ATOMIC_DIO	0x00008000U	/* Want/got atomic_write_* fields for dio */
+#define STATX_WRITE_ATOMIC_BUF	0x00010000U	/* Want/got atomic_write_* fields for non-dio */
 
 #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
 
@@ -197,6 +198,7 @@ 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_DIO	0x00400000 /* File supports atomic write dio operations */
+#define STATX_ATTR_WRITE_ATOMIC_BUF	0x00800000 /* File supports atomic write non-dio operations */
 
 
 #endif /* _UAPI_LINUX_STAT_H */
-- 
2.31.1