Re: [PATCH v4 19/20] libmultipath: enable find_multipaths "smart"

["Benjamin Marzinski" <bmarzins@redhat.com>]

On Wed, Apr 04, 2018 at 06:16:26PM +0200, Martin Wilck wrote:
> This activates "smart" path detection. This is similar to
> "find_multipaths yes", but doesn't generally ignore single paths
> that are not listed in the WWIDs file. Rather, such paths are
> temporarily treated like multipath members. If no additional paths
> are detected after a certain time, the paths are re-added to the
> system as non-multipath. This needs support by the udev rules, to
> be added in a follow-up patch.
> 
> If a multipath map is successfully successfully created, and paths are
> in waiting state, trigger path uevents to update their status.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmultipath/configure.c   | 15 ++++++++++++---
>  libmultipath/dict.c        |  1 +
>  multipath/multipath.conf.5 | 13 +++++++++++++
>  3 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/libmultipath/configure.c b/libmultipath/configure.c
> index 9aa3d21..17c2fa1 100644
> --- a/libmultipath/configure.c
> +++ b/libmultipath/configure.c
> @@ -12,6 +12,7 @@
>  #include <string.h>
>  #include <sys/file.h>
>  #include <errno.h>
> +#include <ctype.h>
>  #include <libdevmapper.h>
>  #include <libudev.h>
>  #include "mpath_cmd.h"
> @@ -476,9 +477,17 @@ trigger_paths_udev_change(struct multipath *mpp, bool is_mpath)
>  			env = udev_device_get_property_value(
>  				pp->udev, "DM_MULTIPATH_DEVICE_PATH");
>  
> -			if (is_mpath && env != NULL && !strcmp(env, "1"))
> -				continue;
> -			else if (!is_mpath &&

If DM_MULTIPATH_DEVICE_PATH=1 then there has already been a uevent where
udev recognized that the device should be claimed.  Wouldn't udev have
stopped the timer then?  I don't see why this is necessary.

> +			if (is_mpath && env != NULL && !strcmp(env, "1")) {
> +				/*
> +				 * If FIND_MULTIPATHS_WAIT_UNTIL is not "0",
> +				 * path is in "maybe" state and timer is running
> +				 * Send uevent now (see multipath.rules).
> +				 */
> +				env = udev_device_get_property_value(
> +					pp->udev, "FIND_MULTIPATHS_WAIT_UNTIL");
> +				if (env == NULL || !strcmp(env, "0"))
> +					continue;
> +			} else if (!is_mpath &&
>  				   (env == NULL || !strcmp(env, "0")))
>  				continue;
>  
> diff --git a/libmultipath/dict.c b/libmultipath/dict.c
> index 4be808d..8a18b1f 100644
> --- a/libmultipath/dict.c
> +++ b/libmultipath/dict.c
> @@ -239,6 +239,7 @@ static const char *find_multipaths_optvals[] = {
>  	[FIND_MULTIPATHS_ON] = "on",
>  	[FIND_MULTIPATHS_STRICT] = "strict",
>  	[FIND_MULTIPATHS_GREEDY] = "greedy",
> +	[FIND_MULTIPATHS_SMART] = "smart",
>  };
>  
>  static int
> diff --git a/multipath/multipath.conf.5 b/multipath/multipath.conf.5
> index 94c419a..641ba43 100644
> --- a/multipath/multipath.conf.5
> +++ b/multipath/multipath.conf.5
> @@ -978,6 +978,19 @@ with the same WWID have been detected.
>  Both multipathd and multipath treat every non-blacklisted device as multipath
>  device path.
>  .TP
> +.I smart
> +This differs from \fIfind_multipaths yes\fR only in
> +the way it treats new devices for which only one path has been
> +detected yet. When such a device is first encounted in udev rules, it is
> +treated as a multipath device. multipathd waits whether additional paths with
> +the same WWID appears. If that happens, it sets up a multipath map. If it
> +doesn\'t happen until a 
> +timeout expires, or if setting up the map fails, a new uevent is triggered for
> +the device; at second encounter in the udev rules, the device will be treated
> +as non-multipath and passed on to upper layers.
> +\fBNote:\fR this may cause delays during device detection if
> +there are single-path devices which aren\'t blacklisted.
> +.TP
>  The default is: \fBstrict\fR
>  .RE
>  .
> -- 
> 2.16.1