vfs: expose STATX_VERSION to userland

Claim one of the spare fields in struct statx to hold a 64-bit inode
version attribute. When userland requests STATX_VERSION, copy the
value from the kstat struct there, and stop masking off
STATX_ATTR_VERSION_MONOTONIC.

Update the test-statx sample program to output the change attr and
MountId.

Signed-off-by: Jeff Layton <jlayton@kernel.org>

fs/stat.c

@@ -605,11 +605,9 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
 
 	memset(&tmp, 0, sizeof(tmp));
 
-	/* STATX_VERSION is kernel-only for now */
-	tmp.stx_mask = stat->result_mask & ~STATX_VERSION;
+	tmp.stx_mask = stat->result_mask;
 	tmp.stx_blksize = stat->blksize;
-	/* STATX_ATTR_VERSION_MONOTONIC is kernel-only for now */
-	tmp.stx_attributes = stat->attributes & ~STATX_ATTR_VERSION_MONOTONIC;
+	tmp.stx_attributes = stat->attributes;
 	tmp.stx_nlink = stat->nlink;
 	tmp.stx_uid = from_kuid_munged(current_user_ns(), stat->uid);
 	tmp.stx_gid = from_kgid_munged(current_user_ns(), stat->gid);
@@ -633,6 +631,7 @@ 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_version = stat->version;
 
 	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
@@ -648,11 +647,6 @@ int do_statx(int dfd, struct filename *filename, unsigned int flags,
 	if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
 		return -EINVAL;
 
-	/* STATX_VERSION is kernel-only for now. Ignore requests
-	 * from userland.
-	 */
-	mask &= ~STATX_VERSION;
-
 	error = vfs_statx(dfd, filename, flags, &stat, mask);
 	if (error)
 		return error;

include/linux/stat.h

@@ -54,13 +54,4 @@ struct kstat {
 	u32		dio_offset_align;
 	u64		version;
 };
-
-/* These definitions are internal to the kernel for now. Mainly used by nfsd. */
-
-/* mask values */
-#define STATX_VERSION		0x40000000U	/* Want/got stx_change_attr */
-
-/* file attribute values */
-#define STATX_ATTR_VERSION_MONOTONIC	0x8000000000000000ULL /* version monotonically increases */
-
 #endif

include/uapi/linux/stat.h

@@ -127,7 +127,8 @@ 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 */
+	__u64	stx_version; /* Inode change attribute */
+	__u64	__spare3[11];	/* Spare space for future expansion */
 	/* 0x100 */
 };
 
@@ -154,6 +155,7 @@ 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_VERSION		0x00004000U	/* Want/got stx_version */
 
 #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
 
@@ -189,6 +191,6 @@ 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_VERSION_MONOTONIC	0x00400000 /* stx_version increases w/ every change */
 
 #endif /* _UAPI_LINUX_STAT_H */

samples/vfs/test-statx.c

@@ -107,6 +107,8 @@ static void dump_statx(struct statx *stx)
 	printf("Device: %-15s", buffer);
 	if (stx->stx_mask & STATX_INO)
 		printf(" Inode: %-11llu", (unsigned long long) stx->stx_ino);
+	if (stx->stx_mask & STATX_MNT_ID)
+		printf(" MountId: %llx", stx->stx_mnt_id);
 	if (stx->stx_mask & STATX_NLINK)
 		printf(" Links: %-5u", stx->stx_nlink);
 	if (stx->stx_mask & STATX_TYPE) {
@@ -145,7 +147,9 @@ static void dump_statx(struct statx *stx)
 	if (stx->stx_mask & STATX_CTIME)
 		print_time("Change: ", &stx->stx_ctime);
 	if (stx->stx_mask & STATX_BTIME)
-		print_time(" Birth: ", &stx->stx_btime);
+		print_time("Birth: ", &stx->stx_btime);
+	if (stx->stx_mask & STATX_VERSION)
+		printf("Inode Version: 0x%llx\n", stx->stx_version);
 
 	if (stx->stx_attributes_mask) {
 		unsigned char bits, mbits;
@@ -218,7 +222,7 @@ int main(int argc, char **argv)
 	struct statx stx;
 	int ret, raw = 0, atflag = AT_SYMLINK_NOFOLLOW;
 
-	unsigned int mask = STATX_BASIC_STATS | STATX_BTIME;
+	unsigned int mask = STATX_BASIC_STATS | STATX_BTIME | STATX_MNT_ID | STATX_VERSION;
 
 	for (argv++; *argv; argv++) {
 		if (strcmp(*argv, "-F") == 0) {