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Date:   Tue, 7 Jan 2020 17:44:07 +0000
From:   Chris Down <chris@chrisdown.name>
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     "Darrick J. Wong" <darrick.wong@oracle.com>,
        linux-fsdevel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
Subject: Re: [PATCH] fs: inode: Reduce volatile inode wraparound risk when
 ino_t is 64 bit
Message-ID: <20200107174407.GA666424@chrisdown.name>
References: <20191220024936.GA380394@chrisdown.name>
 <20191220213052.GB7476@magnolia>
 <20191221101652.GA494948@chrisdown.name>
 <20200107173530.GC944@fieldses.org>
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J. Bruce Fields writes:
>I thought that (dev, inum) was supposed to be unique from creation to
>last unlink (and last close), and (dev, inum, generation) was supposed
>to be unique for all time.

Sure, but I mean, we don't really protect against even the first case.

>> I didn't mention generation because, even though it's set on tmpfs
>> (to prandom_u32()), it's not possible to evaluate it from userspace
>> since `ioctl` returns ENOTTY. We can't ask userspace applications to
>> introspect on an inode attribute that they can't even access :-)
>
>Is there any reason not to add IOC_GETVERSION support to tmpfs?
>
>I wonder if statx should return it too?

We can, but that seems like a tangential discussion/patch series. For the 
second case especially, that's something we should do separately from this 
patchset, since this demonstrably fixes issues encountered in production, and 
extending a user-facing APIs is likely to be a much more extensive discussion.

(Also, this one in particular has advanced quite a lot since this v1 patch :-))