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From:   Florian Weimer <fweimer@redhat.com>
To:     Jeff Layton <jlayton@kernel.org>
Cc:     viro@zeniv.linux.org.uk, linux-api@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        Jeff Layton <jlayton@redhat.com>,
        David Howells <dhowells@redhat.com>,
        Frank Filz <ffilzlnx@mindspring.com>
Subject: Re: [PATCH] vfs: report an inode version in statx for IS_I_VERSION
 inodes
References: <20220819115641.14744-1-jlayton@kernel.org>
Date:   Tue, 23 Aug 2022 12:01:18 +0200
In-Reply-To: <20220819115641.14744-1-jlayton@kernel.org> (Jeff Layton's
        message of "Fri, 19 Aug 2022 07:56:41 -0400")
Message-ID: <87o7wb2s9d.fsf@oldenburg.str.redhat.com>
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* 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?

Thanks,
Florian