Re: [PATCH v3 4/6] btrfs-progs: lowmem check: Add dev_item check for used bytes and total bytes

[Hans van Kranenburg <Hans.van.Kranenburg@mendix.com>]

On 10/08/2018 02:30 PM, Qu Wenruo wrote:
> Obviously, used bytes can't be larger than total bytes.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  check/mode-lowmem.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
> index 07c03cad77af..1173b963b8f3 100644
> --- a/check/mode-lowmem.c
> +++ b/check/mode-lowmem.c
> @@ -4074,6 +4074,11 @@ static int check_dev_item(struct btrfs_fs_info *fs_info,
>  	used = btrfs_device_bytes_used(eb, dev_item);
>  	total_bytes = btrfs_device_total_bytes(eb, dev_item);
>  
> +	if (used > total_bytes) {
> +		error("device %llu has incorrect used bytes %llu > total bytes %llu",
> +			dev_id, used, total_bytes);
> +		return ACCOUNTING_MISMATCH;

The message and return code point at an error in accounting logic.

However, if you have a fully allocated device and a DUP chunk ending
beyond device, then having used > total_bytes is expected...

So maybe there's two possibilities... There's an error in the accounting
logic, or there's an "over-allocation", which is another type of issue
which produces used > total with correct accounting logic.

> +	}
>  	key.objectid = dev_id;
>  	key.type = BTRFS_DEV_EXTENT_KEY;
>  	key.offset = 0;
> 


-- 
Hans van Kranenburg