linux-kernel - [man-pages PATCH] statx, inode: document the new STATX_INO

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Message-Id: <20220826214747.134964-1-jlayton@kernel.org>
Date:   Fri, 26 Aug 2022 17:47:47 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     tytso@....edu, adilger.kernel@...ger.ca, djwong@...nel.org,
        david@...morbit.com, trondmy@...merspace.com, neilb@...e.de,
        viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com,
        chuck.lever@...cle.com, lczerner@...hat.com, jack@...e.cz,
        brauner@...nel.org, linux-man@...r.kernel.org
Cc:     linux-api@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ceph@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: [man-pages PATCH] statx, inode: document the new STATX_INO_VERSION field

We're planning to expose the inode change attribute via statx. Document
what this value means and what an observer can infer from a change in
its value.

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 man2/statx.2 | 13 +++++++++++++
 man7/inode.7 | 10 ++++++++++
 2 files changed, 23 insertions(+)

diff --git a/man2/statx.2 b/man2/statx.2
index 0d1b4591f74c..644fb251f114 100644
--- a/man2/statx.2
+++ b/man2/statx.2
@@ -62,6 +62,7 @@ struct statx {
     __u32 stx_dev_major;   /* Major ID */
     __u32 stx_dev_minor;   /* Minor ID */
     __u64 stx_mnt_id;      /* Mount ID */
+    __u64 stx_ino_version; /* Inode change attribute */
 };
 .EE
 .in
@@ -247,6 +248,7 @@ STATX_BTIME	Want stx_btime
 STATX_ALL	The same as STATX_BASIC_STATS | STATX_BTIME.
 	It is deprecated and should not be used.
 STATX_MNT_ID	Want stx_mnt_id (since Linux 5.8)
+STATX_INO_VERSION	Want stx_ino_version (since Linux 6.1)
 .TE
 .in
 .PP
@@ -411,6 +413,17 @@ and corresponds to the number in the first field in one of the records in
 For further information on the above fields, see
 .BR inode (7).
 .\"
+.TP
+.I stx_ino_version
+The inode version, also known as the inode change attribute. This
+value is intended to change any time there is an inode status change. Any
+operation that would cause the stx_ctime to change should also cause
+stx_ino_version to change, even when there is no apparent change to the
+stx_ctime due to timestamp granularity.
+.IP
+Note that an observer cannot infer anything about the nature or
+magnitude of the change from the value of this field. A change in this value
+only indicates that there may have been an explicit change in the inode.
 .SS File attributes
 The
 .I stx_attributes
diff --git a/man7/inode.7 b/man7/inode.7
index 9b255a890720..d296bb6df70c 100644
--- a/man7/inode.7
+++ b/man7/inode.7
@@ -184,6 +184,16 @@ Last status change timestamp (ctime)
 This is the file's last status change timestamp.
 It is changed by writing or by setting inode information
 (i.e., owner, group, link count, mode, etc.).
+.TP
+Inode version (i_version)
+(not returned in the \fIstat\fP structure); \fIstatx.stx_ino_version\fP
+.IP
+This is the inode change attribute. Any operation that would result in a ctime
+change should also result in a change to this value. The value must change even
+in the case where the ctime change is not evident due to timestamp granularity.
+An observer cannot infer anything from the actual value about the nature or
+magnitude of the change. If it is different from the last time it was checked,
+then something may have made an explicit change to the inode.
 .PP
 The timestamp fields report time measured with a zero point at the
 .IR Epoch ,
-- 
2.37.2