linux-kernel - Re: [PATCH] loop: fix zero sized loop for block special file

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Message-ID: <aKwqUVmX-yH6_lZy@infradead.org>
Date: Mon, 25 Aug 2025 02:18:09 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Ming Lei <ming.lei@...hat.com>
Cc: Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk, rajeevm@....com,
	yukuai3@...wei.com, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
	yangerkun@...wei.com, johnny.chenyi@...wei.com,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] loop: fix zero sized loop for block special file

On Mon, Aug 25, 2025 at 04:56:55PM +0800, Ming Lei wrote:
> `stat $BDEV_PATH` never works for getting bdev size, so it looks wrong
> to call vfs_getattr_nosec() with bdev path for retrieving bdev's size.

Exactly.

> So just wondering why not take the following more readable way?
> 
> 	/* vfs_getattr() never works for retrieving bdev size */
> 	if (S_ISBLK(stat.mode)) {
> 		loopsize = i_size_read(file->f_mapping->host);
> 	} else {
>           ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
>           if (ret)
>                   return 0;
>           loopsize = stat.size;
> 	}
> 
> Also the above looks like how application reads file size in case of bdev
> involved.

That's not just more readable, but simply the way to go.  Maybe split
it into a helper for readability, though.