[LTP] [PATCH] tst_find_backing_dev: fix logic in matching mount point

[Richard Palethorpe]

Hello,

Jan Stancek <jstancek@redhat.com> writes:

> If backing dev is btrfs root device, then starting best_match_len
> from 1 creates an issue, because root (/) is never matched.
> Also we should check that entire mount point string is present in
> path we are matching against.
>
> In case there's error also dump /proc/self/mountinfo before tst_brk.
>
> This fixes test with following partition layout (TMPDIR is on /):
>   # cat /proc/self/mountinfo  | grep btrfs
>   59 1 0:29 /root / rw,relatime shared:1 - btrfs /dev/dasda2 rw,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=257,subvol=/root
>   93 59 0:29 /home /home rw,relatime shared:47 - btrfs /dev/dasda2 rw,seclabel,compress=zstd:1,ssd,space_cache=v2,subvolid=256,subvol=/home
>
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
>  lib/tst_device.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/lib/tst_device.c b/lib/tst_device.c
> index c34cbe6d1f56..414bf0eea816 100644
> --- a/lib/tst_device.c
> +++ b/lib/tst_device.c
> @@ -506,12 +506,17 @@ unsigned long tst_dev_bytes_written(const char *dev)
>  	return dev_bytes_written;
>  }
>  
> -static int count_match_len(const char *first, const char *second)
> +static int str_starts_with(const char *str, const char *prefix)
>  {
>  	int len = 0;
>  
> -	while (*first && *first++ == *second++)
> +	while (*prefix) {
> +		if (!*str)
> +			return 0;
> +		if (*str++ != *prefix++)
> +			return 0;
>  		len++;
> +	}

I'm not sure this is better than the original. It's a seperate cleanup
in any case.

>  
>  	return len;
>  }
> @@ -524,7 +529,7 @@ void tst_find_backing_dev(const char *path, char *dev)
>  	char *pre = NULL;
>  	char *next = NULL;
>  	unsigned int dev_major, dev_minor, line_mjr, line_mnr;
> -	unsigned int len, best_match_len = 1;
> +	unsigned int len, best_match_len = 0;
>  	char mnt_point[PATH_MAX];
>  
>  	if (stat(path, &buf) < 0)
> @@ -550,7 +555,7 @@ void tst_find_backing_dev(const char *path, char *dev)
>  			break;
>  		}
>  
> -		len = count_match_len(path, mnt_point);
> +		len = str_starts_with(path, mnt_point);
>  		if (len > best_match_len) {
>  			strcpy(dev, pre);
>  			best_match_len = len;
> @@ -559,8 +564,10 @@ void tst_find_backing_dev(const char *path, char *dev)
>  
>  	SAFE_FCLOSE(NULL, file);
>  
> -	if (!*dev)
> +	if (!*dev) {
> +		tst_system("cat /proc/self/mountinfo");
>  		tst_brkm(TBROK, NULL, "Cannot find block device for %s", path);
> +	}
>  
>  	if (stat(dev, &buf) < 0)
>  		tst_brkm(TWARN | TERRNO, NULL, "stat(%s) failed", dev);
> -- 
> 2.27.0

Makes sense. However I suspect this function can be replaced with the
standard library method used in tst_stat_mount_dev. I didn't try this
before because I'm not sure why it scans mountinfo instead of mounts.


-- 
Thank you,
Richard.