[PATCH v8 04/10] fs: Add initial 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 for a file.

Helper function generic_fill_statx_atomic_writes() can be used by FSes to
fill in the relevant statx fields. For now atomic_write_segments_max will
always be 1, otherwise some rules would need to be imposed on iovec length
and alignment, which we don't want now.

Signed-off-by: Prasad Singamsetty <prasad.singamsetty at oracle.com>
jpg: relocate bdev support to another patch
Signed-off-by: John Garry <john.g.garry at oracle.com>
---
 fs/stat.c                 | 34 ++++++++++++++++++++++++++++++++++
 include/linux/fs.h        |  3 +++
 include/linux/stat.h      |  3 +++
 include/uapi/linux/stat.h | 12 ++++++++++--
 4 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/fs/stat.c b/fs/stat.c
index 70bd3e888cfa..72d0e6357b91 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -89,6 +89,37 @@ void generic_fill_statx_attr(struct inode *inode, struct kstat *stat)
 }
 EXPORT_SYMBOL(generic_fill_statx_attr);
 
+/**
+ * generic_fill_statx_atomic_writes - Fill in atomic writes statx attributes
+ * @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
+ *
+ * Fill in the STATX{_ATTR}_WRITE_ATOMIC 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)
+{
+	/* Confirm that the request type is known */
+	stat->result_mask |= STATX_WRITE_ATOMIC;
+
+	/* Confirm that the file attribute type is known */
+	stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;
+
+	if (unit_min) {
+		stat->atomic_write_unit_min = unit_min;
+		stat->atomic_write_unit_max = unit_max;
+		/* Initially only allow 1x segment */
+		stat->atomic_write_segments_max = 1;
+
+		/* Confirm atomic writes are actually supported */
+		stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
+	}
+}
+EXPORT_SYMBOL_GPL(generic_fill_statx_atomic_writes);
+
 /**
  * vfs_getattr_nosec - getattr without security checks
  * @path: file to get attributes from
@@ -659,6 +690,9 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
 	tmp.stx_dio_mem_align = stat->dio_mem_align;
 	tmp.stx_dio_offset_align = stat->dio_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;
+	tmp.stx_atomic_write_segments_max = stat->atomic_write_segments_max;
 
 	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e049414bef7d..db26b4a70c62 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3235,6 +3235,9 @@ extern const struct inode_operations page_symlink_inode_operations;
 extern void kfree_link(void *);
 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);
 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/linux/stat.h b/include/linux/stat.h
index bf92441dbad2..3d900c86981c 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -54,6 +54,9 @@ struct kstat {
 	u32		dio_offset_align;
 	u64		change_cookie;
 	u64		subvol;
+	u32		atomic_write_unit_min;
+	u32		atomic_write_unit_max;
+	u32		atomic_write_segments_max;
 };
 
 /* 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 67626d535316..887a25286441 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -126,9 +126,15 @@ struct statx {
 	__u64	stx_mnt_id;
 	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
 	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
-	__u64	stx_subvol;	/* Subvolume identifier */
 	/* 0xa0 */
-	__u64	__spare3[11];	/* Spare space for future expansion */
+	__u64	stx_subvol;	/* Subvolume identifier */
+	__u32	stx_atomic_write_unit_min;	/* Min atomic write unit in bytes */
+	__u32	stx_atomic_write_unit_max;	/* Max atomic write unit in bytes */
+	/* 0xb0 */
+	__u32   stx_atomic_write_segments_max;	/* Max atomic write segment count */
+	__u32   __spare1[1];
+	/* 0xb8 */
+	__u64	__spare3[9];	/* Spare space for future expansion */
 	/* 0x100 */
 };
 
@@ -157,6 +163,7 @@ 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_SUBVOL		0x00008000U	/* Want/got stx_subvol */
+#define STATX_WRITE_ATOMIC	0x00010000U	/* Want/got atomic_write_* fields */
 
 #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
 
@@ -192,6 +199,7 @@ 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