I'm proposing to expose the inode change attribute via statx [1]. Document what this value means and what an observer can infer from it changing. Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> [1]: https://lore.kernel.org/linux-nfs/20220826214703.134870-1-jlayton@xxxxxxxxxx/T/#t --- man2/statx.2 | 17 +++++++++++++++++ man7/inode.7 | 12 ++++++++++++ 2 files changed, 29 insertions(+) v2: revised the definition to be more strict, since that seemed to be consensus on desired behavior. Spurious i_version bumps would now be considered bugs, by this definition. diff --git a/man2/statx.2 b/man2/statx.2 index 0d1b4591f74c..493e4e234809 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 (DRAFT) .TE .in .PP @@ -411,6 +413,21 @@ 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 must change any time there is an inode status change. Any +operation that would cause the +.I stx_ctime +to change must also cause +.I stx_ino_version +to change, even when there is no apparent change to the +.I stx_ctime +due to coarse timestamp granularity. +.IP +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 has 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..d5e0890a52c0 100644 --- a/man7/inode.7 +++ b/man7/inode.7 @@ -184,6 +184,18 @@ 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 change +to \fIstatx.stx_ctime\fP must result in a change to this value. The value must +change even in the case where the ctime change is not evident due to coarse +timestamp granularity. +.IP +An observer cannot infer anything from the returned value about the nature or +magnitude of the change. If the returned value is different from the last time +it was checked, then something has 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
