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Message-ID: <25355.34889.890961.350510@quad.stoffel.home> Date: Sun, 28 Aug 2022 11:22:49 -0400 From: "John Stoffel" <john@...ffel.org> To: Jeff Layton <jlayton@...nel.org> Cc: 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, 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: Re: [man-pages PATCH] statx, inode: document the new STATX_INO_VERSION field >>>>> "Jeff" == Jeff Layton <jlayton@...nel.org> writes: Jeff> We're planning to expose the inode change attribute via statx. Document Jeff> what this value means and what an observer can infer from a change in Jeff> its value. It might be nice to put in some more example verbiage of how this would be used by userland. For example, if you do a statx() call and notice that the ino_version has changed... what would you do next to find out what changed? Would you have to keep around an old copy of the statx() results and then compare them to find the changes? When talking to userland people, don't assume they know anything about the kernel internals here. Jeff> Signed-off-by: Jeff Layton <jlayton@...nel.org> Jeff> --- Jeff> man2/statx.2 | 13 +++++++++++++ Jeff> man7/inode.7 | 10 ++++++++++ Jeff> 2 files changed, 23 insertions(+) Jeff> diff --git a/man2/statx.2 b/man2/statx.2 Jeff> index 0d1b4591f74c..644fb251f114 100644 Jeff> --- a/man2/statx.2 Jeff> +++ b/man2/statx.2 Jeff> @@ -62,6 +62,7 @@ struct statx { Jeff> __u32 stx_dev_major; /* Major ID */ Jeff> __u32 stx_dev_minor; /* Minor ID */ Jeff> __u64 stx_mnt_id; /* Mount ID */ Jeff> + __u64 stx_ino_version; /* Inode change attribute */ Jeff> }; Jeff> .EE Jeff> .in Jeff> @@ -247,6 +248,7 @@ STATX_BTIME Want stx_btime Jeff> STATX_ALL The same as STATX_BASIC_STATS | STATX_BTIME. Jeff> It is deprecated and should not be used. Jeff> STATX_MNT_ID Want stx_mnt_id (since Linux 5.8) Jeff> +STATX_INO_VERSION Want stx_ino_version (since Linux 6.1) Jeff> .TE Jeff> .in Jeff> .PP Jeff> @@ -411,6 +413,17 @@ and corresponds to the number in the first field in one of the records in Jeff> For further information on the above fields, see Jeff> .BR inode (7). Jeff> .\" Jeff> +.TP Jeff> +.I stx_ino_version Jeff> +The inode version, also known as the inode change attribute. This Jeff> +value is intended to change any time there is an inode status change. Any Jeff> +operation that would cause the stx_ctime to change should also cause Jeff> +stx_ino_version to change, even when there is no apparent change to the Jeff> +stx_ctime due to timestamp granularity. Jeff> +.IP Jeff> +Note that an observer cannot infer anything about the nature or Jeff> +magnitude of the change from the value of this field. A change in this value Jeff> +only indicates that there may have been an explicit change in the inode. Jeff> .SS File attributes Jeff> The Jeff> .I stx_attributes Jeff> diff --git a/man7/inode.7 b/man7/inode.7 Jeff> index 9b255a890720..d296bb6df70c 100644 Jeff> --- a/man7/inode.7 Jeff> +++ b/man7/inode.7 Jeff> @@ -184,6 +184,16 @@ Last status change timestamp (ctime) Jeff> This is the file's last status change timestamp. Jeff> It is changed by writing or by setting inode information Jeff> (i.e., owner, group, link count, mode, etc.). Jeff> +.TP Jeff> +Inode version (i_version) Jeff> +(not returned in the \fIstat\fP structure); \fIstatx.stx_ino_version\fP Jeff> +.IP Jeff> +This is the inode change attribute. Any operation that would result in a ctime Jeff> +change should also result in a change to this value. The value must change even Jeff> +in the case where the ctime change is not evident due to timestamp granularity. Jeff> +An observer cannot infer anything from the actual value about the nature or Jeff> +magnitude of the change. If it is different from the last time it was checked, Jeff> +then something may have made an explicit change to the inode. Jeff> .PP Jeff> The timestamp fields report time measured with a zero point at the Jeff> .IR Epoch , Jeff> -- Jeff> 2.37.2
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