[dm-devel] [PATCH 04/33] multipath: do not check daemon from udev rules

[Benjamin Marzinski]

On Tue, Feb 28, 2017 at 05:23:00PM +0100, Martin Wilck wrote:
> From: Hannes Reinecke <hare at suse.de>
> 
> As stated previously, multipathd needs to start after udev trigger
> has run as otherwise it won't be able to find any devices.
> However, this also means that during udevadm trigger the daemon
> wouldn't run, and consequently the check in the udev rules will
> always be false, causing the device not to be marked as multipath
> capable.
> 
> As it turns out, calling 'multipath' from udev rules has quite some
> challenges. It _should_ check if a device is eligible for multipathing.
> But it needs to work under all circumstances, even if the daemon isn't
> running yet, as the program will be called from uevents which might
> (and will) come in before the daemon is running.
> To check if the daemon _should_ be run I'm checking the various
> '.wants' directories from systemd, which carries links to the services
> systemd will enable eventually. So if the multipathd.service is
> listed in there it will be started, even if it isn't started yet.

If we are doing this, so that udev will correctly claim multipath
devices before multipathd has started up, it seems like it should be
possible to relax some of the ordering restrictions for the startup. For
instance, I assume you added the requirement that multipathd needed to
start up before lvmetad to make sure it clamined the devices first.  If
we don't need multipathd to be running to claim the devices, we can
start them up in any order.

-Ben
 
> Signed-off-by: Hannes Reinecke <hare at suse.com>
> ---
>  libmultipath/util.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  libmultipath/util.h |  1 +
>  multipath/main.c    | 13 +++++++-----
>  3 files changed, 68 insertions(+), 5 deletions(-)
> 
> diff --git a/libmultipath/util.c b/libmultipath/util.c
> index 1841f359..be454cb1 100644
> --- a/libmultipath/util.c
> +++ b/libmultipath/util.c
> @@ -6,13 +6,16 @@
>  #include <sys/stat.h>
>  #include <sys/sysmacros.h>
>  #include <sys/types.h>
> +#include <dirent.h>
>  #include <unistd.h>
> +#include <errno.h>
>  
>  #include "debug.h"
>  #include "memory.h"
>  #include "checkers.h"
>  #include "vector.h"
>  #include "structs.h"
> +#include "log.h"
>  
>  size_t
>  strchop(char *str)
> @@ -279,3 +282,59 @@ setup_thread_attr(pthread_attr_t *attr, size_t stacksize, int detached)
>  		assert(ret == 0);
>  	}
>  }
> +
> +int systemd_service_enabled_in(const char *dev, const char *prefix)
> +{
> +	char path[PATH_SIZE], file[PATH_SIZE], service[PATH_SIZE];
> +	DIR *dirfd;
> +	struct dirent *d;
> +	int found = 0;
> +
> +	snprintf(service, PATH_SIZE, "multipathd.service");
> +	snprintf(path, PATH_SIZE, "%s/systemd/system", prefix);
> +	condlog(3, "%s: checking for %s in %s", dev, service, path);
> +
> +	dirfd = opendir(path);
> +	if (dirfd == NULL)
> +		return 0;
> +
> +	while ((d = readdir(dirfd)) != NULL) {
> +		char *p;
> +		struct stat stbuf;
> +
> +		if ((strcmp(d->d_name,".") == 0) ||
> +		    (strcmp(d->d_name,"..") == 0))
> +			continue;
> +
> +		if (strlen(d->d_name) < 6)
> +			continue;
> +
> +		p = d->d_name + strlen(d->d_name) - 6;
> +		if (strcmp(p, ".wants"))
> +			continue;
> +		snprintf(file, PATH_SIZE, "%s/%s/%s",
> +			 path, d->d_name, service);
> +		if (stat(file, &stbuf) == 0) {
> +			condlog(3, "%s: found %s", dev, file);
> +			found++;
> +			break;
> +		}
> +	}
> +	closedir(dirfd);
> +
> +	return found;
> +}
> +
> +int systemd_service_enabled(const char *dev)
> +{
> +	int found = 0;
> +
> +	found = systemd_service_enabled_in(dev, "/etc");
> +	if (!found)
> +		found = systemd_service_enabled_in(dev, "/usr/lib");
> +	if (!found)
> +		found = systemd_service_enabled_in(dev, "/lib");
> +	if (!found)
> +		found = systemd_service_enabled_in(dev, "/run");
> +	return found;
> +}
> diff --git a/libmultipath/util.h b/libmultipath/util.h
> index f3b37ee9..4c1f85c3 100644
> --- a/libmultipath/util.h
> +++ b/libmultipath/util.h
> @@ -13,6 +13,7 @@ int devt2devname (char *, int, char *);
>  dev_t parse_devt(const char *dev_t);
>  char *convert_dev(char *dev, int is_path_device);
>  void setup_thread_attr(pthread_attr_t *attr, size_t stacksize, int detached);
> +int systemd_service_enabled(const char *dev);
>  
>  #define safe_sprintf(var, format, args...)	\
>  	snprintf(var, sizeof(var), format, ##args) >= sizeof(var)
> diff --git a/multipath/main.c b/multipath/main.c
> index 171c08b4..befe4c53 100644
> --- a/multipath/main.c
> +++ b/multipath/main.c
> @@ -682,11 +682,14 @@ main (int argc, char *argv[])
>  
>  		fd = mpath_connect();
>  		if (fd == -1) {
> -			printf("%s is not a valid multipath device path\n",
> -				dev);
> -			goto out;
> -		}
> -		mpath_disconnect(fd);
> +			condlog(3, "%s: daemon is not running", dev);
> +			if (!systemd_service_enabled(dev)) {
> +				printf("%s is not a valid "
> +				       "multipath device path\n", dev);
> +				goto out;
> +			}
> +		} else
> +			mpath_disconnect(fd);
>  	}
>  	if (cmd == CMD_REMOVE_WWID && !dev) {
>  		condlog(0, "the -w option requires a device");
> -- 
> 2.11.0
> 
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