On Mon, Aug 25, 2025 at 02:23:00PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> By default, /dev/sda is block specail file from devtmpfs, getattr will
> return file size as zero, causing loop failed for raw block device.
>
> We can add bdev_statx() to return device size, however this may introduce
> changes that are not acknowledged by user. Fix this problem by reverting
> changes for block special file, file mapping host is set to bdev inode
> while opening, and use i_size_read() directly to get device size.
>
> Fixes: 47b71abd5846 ("loop: use vfs_getattr_nosec for accurate file size")
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202508200409.b2459c02-lkp@xxxxxxxxx
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
> drivers/block/loop.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 57263c273f0f..cde235bd883c 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -153,6 +153,9 @@ static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
> return 0;
>
> loopsize = stat.size;
> + if (!loopsize && S_ISBLK(stat.mode))
> + loopsize = i_size_read(file->f_mapping->host);
`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.
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.
Thanks,
Ming
