Re: [PATCH] btrfs-progs: Force 'btrfs dev scan' not using old libblkid cache

[Anand Jain <Anand.Jain@oracle.com>]

On 04/10/2014 03:30 PM, Qu Wenruo wrote:
> 'btrfs scan' uses libblkid to scan devices by default, and libblkid uses
> cache to reduce the probe.
>
> But if operations below is done in less than 2 seconds(BLKID_PROBE_MIN),
> 'btrfs scan' will still use the uncorrect cache and scan on the deleted device.

  Great thanks for looking into this.

Anand


> 0. /dev/sda[1-4] mounted on /mnt using single data/metadata
> 1. btrfs dev scan
> 2. btrfs dev del /dev/sda3 /mnt
> 3. btrfs dev scan

> Since the cache made by step 1 is still validated, step 3 will use the
> cache and consider /dev/sda3 as a btrfs filesystem and try to scan it.
> But the superblock(at least the first one) is wiped and failed to scan,
> a error message, which can be avoided and is unneeded, is output.
>
> This patch will force scan_for_btrfs() not to use cache to avoid the
> problem.
>
> Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
> Singed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
>   utils.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/utils.c b/utils.c
> index 0bfb9d9..1cd1d28 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -2057,7 +2057,8 @@ int btrfs_scan_lblkid(int update_kernel)
>   	blkid_cache cache = NULL;
>   	char path[PATH_MAX];
>
> -	if (blkid_get_cache(&cache, 0) < 0) {
> +	/* No to use libblkid cache to avoid old data */
> +	if (blkid_get_cache(&cache, "/dev/null") < 0) {
>   		printf("ERROR: lblkid cache get failed\n");
>   		return 1;
>   	}
>