[PATCH RFC 02/16] fs/bdev: Add atomic write support info to statx

[John Garry]

From: Prasad Singamsetty <prasad.singamsetty at oracle.com>

Extend statx system call to return additional info for atomic write support
support if the specified file is a block device.

Add initial support for a block device.

Signed-off-by: Prasad Singamsetty <prasad.singamsetty at oracle.com>
Signed-off-by: John Garry <john.g.garry at oracle.com>
---
 block/bdev.c              | 21 +++++++++++++++++++++
 fs/stat.c                 | 10 ++++++++++
 include/linux/blkdev.h    |  4 ++++
 include/linux/stat.h      |  2 ++
 include/uapi/linux/stat.h |  7 ++++++-
 5 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/block/bdev.c b/block/bdev.c
index 1795c7d4b99e..6a5fd5abaadc 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1014,3 +1014,24 @@ void bdev_statx_dioalign(struct inode *inode, struct kstat *stat)
 
 	blkdev_put_no_open(bdev);
 }
+
+/*
+ * Handle statx for block devices to get properties of WRITE ATOMIC
+ * feature support.
+ */
+void bdev_statx_atomic(struct inode *inode, struct kstat *stat)
+{
+	struct block_device *bdev;
+
+	bdev = blkdev_get_no_open(inode->i_rdev);
+	if (!bdev)
+		return;
+
+	stat->atomic_write_unit_min = queue_atomic_write_unit_min(bdev->bd_queue);
+	stat->atomic_write_unit_max = queue_atomic_write_unit_max(bdev->bd_queue);
+	stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
+	stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;
+	stat->result_mask |= STATX_WRITE_ATOMIC;
+
+	blkdev_put_no_open(bdev);
+}
diff --git a/fs/stat.c b/fs/stat.c
index 7c238da22ef0..d20334a0e9ae 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -256,6 +256,14 @@ static int vfs_statx(int dfd, struct filename *filename, int flags,
 			bdev_statx_dioalign(inode, stat);
 	}
 
+	/* Handle STATX_WRITE_ATOMIC for block devices */
+	if (request_mask & STATX_WRITE_ATOMIC) {
+		struct inode *inode = d_backing_inode(path.dentry);
+
+		if (S_ISBLK(inode->i_mode))
+			bdev_statx_atomic(inode, stat);
+	}
+
 	path_put(&path);
 	if (retry_estale(error, lookup_flags)) {
 		lookup_flags |= LOOKUP_REVAL;
@@ -636,6 +644,8 @@ 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_atomic_write_unit_min = stat->atomic_write_unit_min;
+	tmp.stx_atomic_write_unit_max = stat->atomic_write_unit_max;
 
 	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6b6f2992338c..19d33b2897b2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1527,6 +1527,7 @@ int sync_blockdev_range(struct block_device *bdev, loff_t lstart, loff_t lend);
 int sync_blockdev_nowait(struct block_device *bdev);
 void sync_bdevs(bool wait);
 void bdev_statx_dioalign(struct inode *inode, struct kstat *stat);
+void bdev_statx_atomic(struct inode *inode, struct kstat *stat);
 void printk_all_partitions(void);
 #else
 static inline void invalidate_bdev(struct block_device *bdev)
@@ -1546,6 +1547,9 @@ static inline void sync_bdevs(bool wait)
 static inline void bdev_statx_dioalign(struct inode *inode, struct kstat *stat)
 {
 }
+static inline void bdev_statx_atomic(struct inode *inode, struct kstat *stat)
+{
+}
 static inline void printk_all_partitions(void)
 {
 }
diff --git a/include/linux/stat.h b/include/linux/stat.h
index 52150570d37a..dfa69ecfaacf 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -53,6 +53,8 @@ struct kstat {
 	u32		dio_mem_align;
 	u32		dio_offset_align;
 	u64		change_cookie;
+	u32		atomic_write_unit_max;
+	u32		atomic_write_unit_min;
 };
 
 /* These definitions are internal to the kernel for now. Mainly used by nfsd. */
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index 7cab2c65d3d7..c99d7cac2aa6 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -127,7 +127,10 @@ struct statx {
 	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
 	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
 	/* 0xa0 */
-	__u64	__spare3[12];	/* Spare space for future expansion */
+	__u32	stx_atomic_write_unit_max;
+	__u32	stx_atomic_write_unit_min;
+	/* 0xb0 */
+	__u64	__spare3[11];	/* Spare space for future expansion */
 	/* 0x100 */
 };
 
@@ -154,6 +157,7 @@ struct statx {
 #define STATX_BTIME		0x00000800U	/* Want/got stx_btime */
 #define STATX_MNT_ID		0x00001000U	/* Got stx_mnt_id */
 #define STATX_DIOALIGN		0x00002000U	/* Want/got direct I/O alignment info */
+#define STATX_WRITE_ATOMIC	0x00004000U	/* Want/got atomic_write_* fields */
 
 #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
 
@@ -189,6 +193,7 @@ struct statx {
 #define STATX_ATTR_MOUNT_ROOT		0x00002000 /* Root of a mount */
 #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 */
 
 
 #endif /* _UAPI_LINUX_STAT_H */
-- 
2.31.1