[PATCH v4 04/11] fs: Add initial atomic write support info to statx

John Garry
2024-02-19T13:04:44Z

From: Prasad Singamsetty <prasad.singamsetty@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.

Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
#jpg: relocate bdev support to another patch
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/stat.c | 34 ++++++++++++++++++++++++++++++++++
include/linux/fs.h | 3 +++
include/linux/stat.h | 3 +++
include/uapi/linux/stat.h | 9 ++++++++-
4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/fs/stat.c b/fs/stat.c
index 77cdc69eb422..522787a4ab6a 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 the atomic writes statx attributes
+ * @stat: Where to fill in the attribute flags
+ * @unit_min: Minimum supported atomic write length
+ * @unit_max: Maximum supported atomic write length
+ *
+ * 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(generic_fill_statx_atomic_writes);
+
/**
* vfs_getattr_nosec - getattr without security checks
* @path: file to get attributes from
@@ -658,6 +689,9 @@ 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;
+ 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 7271640fd600..531140a7e27a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3167,6 +3167,9 @@ 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 52150570d37a..2c5e2b8c6559 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -53,6 +53,9 @@ struct kstat {
u32 dio_mem_align;
u32 dio_offset_align;
u64 change_cookie;
+ 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 2f2ee82d5517..c0e8e10d1de6 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -127,7 +127,12 @@ 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_min;
+ __u32 stx_atomic_write_unit_max;
+ __u32 stx_atomic_write_segments_max;
+ __u32 __spare1;
+ /* 0xb0 */
+ __u64 __spare3[10]; /* Spare space for future expansion */
/* 0x100 */
};

@@ -155,6 +160,7 @@ struct statx {
#define STATX_MNT_ID 0x00001000U /* Got stx_mnt_id */
#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 0x00008000U /* Want/got atomic_write_* fields */

#define STATX__RESERVED 0x80000000U /* Reserved for future struct statx expansion */

@@ -190,6 +196,7 @@ 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