linux-kernel - Re: [PATCH v2] loop: fix zero sized loop for block special file

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Message-ID: <36f30d8d-02fb-4579-b527-16da24cdc856@kernel.dk>
Date: Mon, 25 Aug 2025 07:56:02 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Yu Kuai <yukuai1@...weicloud.com>, ming.lei@...hat.com,
 hch@...radead.org, yukuai3@...wei.com, rajeevm@....com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH v2] loop: fix zero sized loop for block special file

On 8/25/25 3:32 AM, Yu Kuai wrote:
>  static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
>  {
> -	struct kstat stat;
>  	loff_t loopsize;
>  	int ret;
>  
> -	/*
> -	 * Get the accurate file size. This provides better results than
> -	 * cached inode data, particularly for network filesystems where
> -	 * metadata may be stale.
> -	 */
> -	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
> -	if (ret)
> -		return 0;
> +	if (S_ISBLK(file_inode(file)->i_mode)) {
> +		loopsize = i_size_read(file->f_mapping->host);
> +	} else {
> +		struct kstat stat;
> +
> +		/*
> +		 * Get the accurate file size. This provides better results than
> +		 * cached inode data, particularly for network filesystems where
> +		 * metadata may be stale.
> +		 */
> +		ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
> +		if (ret)
> +			return 0;
> +
> +		loopsize = stat.size;
> +	}

Gah, that was pretty silly...

-- 
Jens Axboe