[PATCH] statx.2: Document STATX_SUBVOL

[Kent Overstreet <kent.overstreet@linux.dev>]

Document the new statxt.stx_subvol field.

This would be clearer if we had a proper API for walking subvolumes that
we could refer to, but that's still coming.

Link: https://lore.kernel.org/linux-fsdevel/20240308022914.196982-1-kent.overstreet@linux.dev/
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Alejandro Colomar <alx@kernel.org>
Cc: linux-man@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
---
 man2/statx.2 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/man2/statx.2 b/man2/statx.2
index 0dcf7e20bb1f..480e69b46a89 100644
--- a/man2/statx.2
+++ b/man2/statx.2
@@ -68,6 +68,7 @@ struct statx {
     /* Direct I/O alignment restrictions */
     __u32 stx_dio_mem_align;
     __u32 stx_dio_offset_align;
+    __u64 stx_subvol;      /* Subvolume identifier */
 };
 .EE
 .in
@@ -255,6 +256,8 @@ STATX_ALL	The same as STATX_BASIC_STATS | STATX_BTIME.
 STATX_MNT_ID	Want stx_mnt_id (since Linux 5.8)
 STATX_DIOALIGN	Want stx_dio_mem_align and stx_dio_offset_align
 	(since Linux 6.1; support varies by filesystem)
+STATX_SUBVOL	Wants stx_subvol
+	(since Linux 6.9; support varies by filesystem)
 .TE
 .in
 .P
@@ -439,6 +442,11 @@ or 0 if direct I/O is not supported on this file.
 This will only be nonzero if
 .I stx_dio_mem_align
 is nonzero, and vice versa.
+.TP
+.I stx_subvolume
+Subvolume number of the current file.
+
+Subvolumes are fancy directories, i.e. they form a tree structure that may be walked recursively.
 .P
 For further information on the above fields, see
 .BR inode (7).
-- 
2.43.0