linux-kernel - Re: [PATCH] UBIFS: fill f

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Date:	Mon, 01 Sep 2008 10:43:07 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Artem Bityutskiy <dedekind@...radead.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Adrian Hunter <ext-adrian.hunter@...ia.com>
Subject: Re: [PATCH] UBIFS: fill f_fsid

On Sun, 2008-08-31 at 17:52 +0300, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
> 
> UBIFS stores 16-bit UUID in the superblock, and it is a good
> idea to return part of it in 'f_fsid' filed of kstatfs structure.

I think you mean a 16-byte UUID, not 16-bit?

> +	memcpy(&buf->f_fsid, c->uuid, sizeof(__kernel_fsid_t));

For btrfs I xor the first 64 bits with the second 64 bits, and put
_that_ into f_fsid. You're just putting the first 64 bits in and
ignoring the second 64 bits. Neither is really _better_ than the other;
you just alter the circumstances in which you get collisions. But I
suppose we might as well be consistent about how we do it?

(Actually I XOR in the root object ID for the subvol too, but you don't
need to worry about that).

Alternatively, there's space in the struct statfs to export a couple
more uint32_ts, and thus the _whole_ of the uuid. Perhaps we should do
that?

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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