[dm-devel] [RFC PATCH v2 2/3] libmultipath: make sysfs_is_multipathed able to return wwid

[Martin Wilck]

On Fri, 2020-04-03 at 01:50 -0500, Benjamin Marzinski wrote:
> sysfs_is_multipathed reads the wwid of the dm device holding a path
> to
> check if its a multipath device.  Add code to optinally set pp->wwid
> to
> that wwid.  This will be used by a future patch.
> 
> Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
> ---
>  libmultipath/sysfs.c | 24 +++++++++++++++++++-----
>  libmultipath/sysfs.h |  2 +-
>  multipath/main.c     |  7 ++++---
>  3 files changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/libmultipath/sysfs.c b/libmultipath/sysfs.c
> index 62ec2ed7..12a82d95 100644
> --- a/libmultipath/sysfs.c
> +++ b/libmultipath/sysfs.c
> @@ -295,7 +295,7 @@ static int select_dm_devs(const struct dirent
> *di)
>  	return fnmatch("dm-*", di->d_name, FNM_FILE_NAME) == 0;
>  }
>  
> -bool sysfs_is_multipathed(const struct path *pp)
> +bool sysfs_is_multipathed(struct path *pp, bool set_wwid)
>  {
>  	char pathbuf[PATH_MAX];
>  	struct scandir_result sr;
> @@ -325,7 +325,7 @@ bool sysfs_is_multipathed(const struct path *pp)
>  	for (i = 0; i < r && !found; i++) {
>  		long fd;
>  		int nr;
> -		char uuid[6];
> +		char uuid[WWID_SIZE + UUID_PREFIX_LEN];
>  
>  		if (safe_snprintf(pathbuf + n, sizeof(pathbuf) - n,
>  				  "/%s/dm/uuid", di[i]->d_name))
> @@ -339,12 +339,26 @@ bool sysfs_is_multipathed(const struct path
> *pp)
>  
>  		pthread_cleanup_push(close_fd, (void *)fd);
>  		nr = read(fd, uuid, sizeof(uuid));
> -		if (nr == sizeof(uuid) && !memcmp(uuid, "mpath-",
> sizeof(uuid)))
> +		if (nr > (int)UUID_PREFIX_LEN &&
> +		    !memcmp(uuid, UUID_PREFIX, UUID_PREFIX_LEN))
>  			found = true;
>  		else if (nr < 0) {
> -			condlog(1, "%s: error reading from %s: %s",
> -				__func__, pathbuf, strerror(errno));
> +			condlog(1, "%s: error reading from %s: %m",
> +				__func__, pathbuf);
>  		}
> +		if (found && set_wwid) {
> +			nr -= UUID_PREFIX_LEN;
> +			memcpy(pp->wwid, uuid + UUID_PREFIX_LEN, nr);
> +			if (nr == WWID_SIZE) {
> +				condlog(4, "%s: overflow while reading
> from %s",
> +					__func__, pathbuf);

I would have checked this condition before calling memcpy(), but that's
just a nit.

Reviewed-by: Martin Wilck <mwilck at suse.com>

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE  Software Solutions Germany GmbH
HRB 36809, AG Nürnberg GF: Felix
Imendörffer