linux-kernel - Re: [PATCH v2] loop: use vfs_getattr

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Message-ID: <a7cb5d59-8af5-47b2-8549-05c9322971e5@kernel.org>
Date: Tue, 12 Aug 2025 14:17:01 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Rajeev Mishra <rajeevm@....com>, axboe@...nel.dk,
 yukuai1@...weicloud.com, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] loop: use vfs_getattr_nosec() for accurate file size

On 8/12/25 1:28 PM, Al Viro wrote:
> On Tue, Aug 12, 2025 at 12:42:44PM +0900, Damien Le Moal wrote:
> 
>> Since loff_t is "long long", so a signed type, I would keep this interface and
>> add a negative error check in the 2 call sites for get_size(). That is simpler.
> 
> Umm...  First of all, what's the point of separate get_size() and loop_get_size()?
> Another thing to watch out for - replacing file needs to be careful, lest you
> replace the old file that has come to fail vfs_getattr() with new one that
> does the same thing ;-)

I did a quick grep and missed the fact that get_size() is mostly used through
get_loop_size(). So yes, making these 2 a single function will be clearer.

And indeed, that:

	/* size of the new backing store needs to be the same */
        if (get_loop_size(lo, file) != get_loop_size(lo, old_file))
                goto out_err;

Will need some massaging.


-- 
Damien Le Moal
Western Digital Research