Re: [PATCH] vfs: report an inode version in statx for IS_I_VERSION inodes

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2022-08-23 at 12:01 +0200, Florian Weimer wrote:
> * Jeff Layton:
> 
> > From: Jeff Layton <jlayton@redhat.com>
> > 
> > The NFS server and IMA both rely heavily on the i_version counter, but
> > it's largely invisible to userland, which makes it difficult to test its
> > behavior. This value would also be of use to userland NFS servers, and
> > other applications that want a reliable way to know if there was an
> > explicit change to an inode since they last checked.
> > 
> > Claim one of the spare fields in struct statx to hold a 64-bit inode
> > version attribute. This value must change with any explicit, observeable
> > metadata or data change. Note that atime updates are excluded from this,
> > unless it is due to an explicit change via utimes or similar mechanism.
> > 
> > When statx requests this attribute on an IS_I_VERSION inode, do an
> > inode_query_iversion and fill the result in the field. Also, update the
> > test-statx.c program to display the inode version and the mountid.
> 
> Will the version survive reboots?  Is it stored on disks?  Can backup
> tools (and others) use this to check if the file has changed since the
> last time the version has been observed?
> 


The answer to all of those question is "yes".
-- 
Jeff Layton <jlayton@kernel.org>