Re: [PATCH v2] libmpathpersist: fix code for skipping multipathd path registration

[Benjamin Marzinski <bmarzins@redhat.com>]

On Tue, Dec 09, 2025 at 01:01:27PM +0100, Martin Wilck wrote:
> On Mon, 2025-12-08 at 16:12 -0500, Benjamin Marzinski wrote:
> > When libmpathpersist notifies multipathd that a key has been
> > registered,
> > cli_setprstatus() calls pr_register_active_paths() with a flag to let
> > it
> > know that the paths are likely already registered, and it can skip
> > re-registering them, as long as the number of active paths matches
> > the
> > number of registered keys. This shortcut can fail, causing multipathd
> > to
> > not register needed paths, if either a path becomes usable and
> > another
> > becomes unusable while libmpathpersist is running or if there already
> > were registered keys for I_T Nexus's that don't correspond to path
> > devices.
> > 
> > To make this shortcut work in cases like that, this commit adds a new
> > multipathd command "setprstatus map <map> pathlist <pathlist>", where
> > <pathlist> is a quoted, comma separated list of scsi path devices.
> > libmpathpersist will send out the list of paths it registered the key
> > on. pr_register_active_paths() will skip calling
> > mpath_pr_event_handle()
> > for paths on that list.
> > 
> > In order to deal with the possiblity of a preempt occuring while
> > libmpathpersist was running, the code still needs to check that it
> > has
> > the expected number of keys.
> > 
> > Fixes: f7d6cd17 ("multipathd: Fix race while registering PR key")
> > Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
> 
> Minor comments below.
> 
> Regards,
> Martin
> 
> 
> 
> > ---
> > 
> > Was patch 4/4 of "multipath-tools: Yet Another PR fix"
> > Changes in v2 (assuming we agree to use this patch at all):
> > added a semi-colon after the "skip" label to make clang happy.
> > 
> >  libmpathpersist/mpath_persist_int.c |  6 +--
> >  libmpathpersist/mpath_updatepr.c    | 48 +++++++++++++++++-----
> >  libmpathpersist/mpathpr.h           |  4 +-
> >  multipathd/callbacks.c              |  1 +
> >  multipathd/cli.c                    |  1 +
> >  multipathd/cli.h                    |  2 +
> >  multipathd/cli_handlers.c           | 39 ++++++++++++++++--
> >  multipathd/main.c                   | 62 +++++++++++++++++++--------
> > --
> >  multipathd/main.h                   |  3 +-
> >  multipathd/multipathd.8.in          |  6 +++
> >  10 files changed, 133 insertions(+), 39 deletions(-)
> > 
> > diff --git a/libmpathpersist/mpath_persist_int.c
> > b/libmpathpersist/mpath_persist_int.c
> > index 91c53419..14f7ba83 100644
> > --- a/libmpathpersist/mpath_persist_int.c
> > +++ b/libmpathpersist/mpath_persist_int.c
> > @@ -1001,12 +1001,12 @@ int do_mpath_persistent_reserve_out(vector
> > curmp, vector pathvec, int fd,
> >  	case MPATH_PROUT_REG_SA:
> >  	case MPATH_PROUT_REG_IGN_SA:
> >  		if (unregistering)
> > -			update_prflag(mpp->alias, 0);
> > +			update_prflag(mpp, 0);
> >  		else
> > -			update_prflag(mpp->alias, 1);
> > +			update_prflag(mpp, 1);
> >  		break;
> >  	case MPATH_PROUT_CLEAR_SA:
> > -		update_prflag(mpp->alias, 0);
> > +		update_prflag(mpp, 0);
> >  		if (mpp->prkey_source == PRKEY_SOURCE_FILE)
> >  			update_prkey(mpp->alias, 0);
> >  		break;
> > diff --git a/libmpathpersist/mpath_updatepr.c
> > b/libmpathpersist/mpath_updatepr.c
> > index bd8ed2be..bc9c79e2 100644
> > --- a/libmpathpersist/mpath_updatepr.c
> > +++ b/libmpathpersist/mpath_updatepr.c
> > @@ -20,8 +20,9 @@
> >  #include "uxsock.h"
> >  #include "mpathpr.h"
> >  #include "structs.h"
> > +#include "strbuf.h"
> >  
> > -static char *do_pr(char *alias, char *str)
> > +static char *do_pr(char *alias, const char *str)
> >  {
> >  	int fd;
> >  	char *reply;
> > @@ -51,24 +52,27 @@ static char *do_pr(char *alias, char *str)
> >  	return reply;
> >  }
> >  
> > -static int do_update_pr(char *alias, char *cmd, char *key)
> > +static int do_update_pr(char *alias, char *cmd, const char *data)
> >  {
> > -	char str[256];
> > +	STRBUF_ON_STACK(buf);
> >  	char *reply = NULL;
> >  	int ret = -1;
> >  
> > -	if (key)
> > -		snprintf(str, sizeof(str), "%s map %s key %s", cmd,
> > alias, key);
> > +	if (data)
> > +		print_strbuf(&buf, "%s map %s %s %s", cmd, alias,
> > +			     strcmp(cmd, "setprkey") ? "pathlist" :
> > "key",
> > +			     data);
> >  	else
> > -		snprintf(str, sizeof(str), "%s map %s", cmd, alias);
> > +		print_strbuf(&buf, "%s map %s", cmd, alias);
> >  
> > -	reply = do_pr(alias, str);
> > +	reply = do_pr(alias, get_strbuf_str(&buf));
> >  	if (reply) {
> >  		if (strncmp(reply, "ok", 2) == 0)
> >  			ret = 0;
> >  		else
> >  			ret = -1;
> > -		condlog(ret ? 0 : 4, "%s: message=%s reply=%s",
> > alias, str, reply);
> > +		condlog(ret ? 0 : 4, "%s: message=%s reply=%s",
> > alias,
> > +			get_strbuf_str(&buf), reply);
> >  	}
> >  
> >  	free(reply);
> > @@ -106,9 +110,31 @@ int get_prhold(char *mapname)
> >  	return do_get_pr(mapname, "getprhold");
> >  }
> >  
> > -int update_prflag(char *mapname, int set) {
> > -	return do_update_pr(mapname, (set)? "setprstatus" :
> > "unsetprstatus",
> > -			    NULL);
> > +int update_prflag(struct multipath *mpp, int set)
> > +{
> > +	STRBUF_ON_STACK(buf);
> > +	int i, j;
> > +	bool first = true;
> > +	struct pathgroup *pgp = NULL;
> > +	struct path *pp = NULL;
> > +
> > +	if (!set)
> > +		return do_update_pr(mpp->alias, "unsetprstatus",
> > NULL);
> > +
> > +	append_strbuf_str(&buf, "\"");
> > +	vector_foreach_slot (mpp->pg, pgp, j) {
> > +		vector_foreach_slot (pgp->paths, pp, i) {
> > +			if (pp->state == PATH_UP || pp->state ==
> > PATH_GHOST) {
> > +				if (first) {
> > +					append_strbuf_str(&buf, pp-
> > >dev);
> > +					first = false;
> > +				} else
> > +					print_strbuf(&buf, " %s",
> > pp->dev);
> 
> Nitpick: in the commit description you said the list was comma-
> separated, here it looks like space-separated.

Oops. I'll fix that.
 
> Also, I'd prefer to use pp->dev_t here unless there are good reasons
> against that.

Sure. I have no preference. 

> > +			}
> > +		}
> > +	}
> > +	append_strbuf_str(&buf, "\"");
> > +	return do_update_pr(mpp->alias, "setprstatus",
> > get_strbuf_str(&buf));
> >  }
> >  
> >  int update_prhold(char *mapname, bool set)
> > diff --git a/libmpathpersist/mpathpr.h b/libmpathpersist/mpathpr.h
> > index 99d6b82f..adbfc865 100644
> > --- a/libmpathpersist/mpathpr.h
> > +++ b/libmpathpersist/mpathpr.h
> > @@ -1,12 +1,14 @@
> >  #ifndef MPATHPR_H_INCLUDED
> >  #define MPATHPR_H_INCLUDED
> >  
> > +#include "structs.h"
> > +
> >  /*
> >   * This header file contains symbols that are only used by
> >   * libmpathpersist internally.
> >   */
> >  
> > -int update_prflag(char *mapname, int set);
> > +int update_prflag(struct multipath *mpp, int set);
> >  int update_prkey_flags(char *mapname, uint64_t prkey, uint8_t
> > sa_flags);
> >  int get_prflag(char *mapname);
> >  int get_prhold(char *mapname);
> > diff --git a/multipathd/callbacks.c b/multipathd/callbacks.c
> > index b6b57f45..1129855b 100644
> > --- a/multipathd/callbacks.c
> > +++ b/multipathd/callbacks.c
> > @@ -59,6 +59,7 @@ void init_handler_callbacks(void)
> >  	set_unlocked_handler_callback(VRB_SHUTDOWN,
> > HANDLER(cli_shutdown));
> >  	set_handler_callback(VRB_GETPRSTATUS | Q1_MAP,
> > HANDLER(cli_getprstatus));
> >  	set_handler_callback(VRB_SETPRSTATUS | Q1_MAP,
> > HANDLER(cli_setprstatus));
> > +	set_handler_callback(VRB_SETPRSTATUS | Q1_MAP | Q2_PATHLIST,
> > HANDLER(cli_setprstatus_list));
> >  	set_handler_callback(VRB_UNSETPRSTATUS | Q1_MAP,
> > HANDLER(cli_unsetprstatus));
> >  	set_handler_callback(VRB_FORCEQ | Q1_DAEMON,
> > HANDLER(cli_force_no_daemon_q));
> >  	set_handler_callback(VRB_RESTOREQ | Q1_DAEMON,
> > HANDLER(cli_restore_no_daemon_q));
> > diff --git a/multipathd/cli.c b/multipathd/cli.c
> > index d0e6cebc..0d679c86 100644
> > --- a/multipathd/cli.c
> > +++ b/multipathd/cli.c
> > @@ -227,6 +227,7 @@ load_keys (void)
> >  	r += add_key(keys, "getprhold", VRB_GETPRHOLD, 0);
> >  	r += add_key(keys, "setprhold", VRB_SETPRHOLD, 0);
> >  	r += add_key(keys, "unsetprhold", VRB_UNSETPRHOLD, 0);
> > +	r += add_key(keys, "pathlist", KEY_PATHLIST, 1);
> >  
> >  	if (r) {
> >  		free_keys(keys);
> > diff --git a/multipathd/cli.h b/multipathd/cli.h
> > index 5a943a45..3e607389 100644
> > --- a/multipathd/cli.h
> > +++ b/multipathd/cli.h
> > @@ -62,6 +62,7 @@ enum {
> >  	KEY_LOCAL		= 81,
> >  	KEY_GROUP		= 82,
> >  	KEY_KEY			= 83,
> > +	KEY_PATHLIST		= 84,
> >  };
> >  
> >  /*
> > @@ -94,6 +95,7 @@ enum {
> >  	Q2_LOCAL		= KEY_LOCAL << 16,
> >  	Q2_GROUP		= KEY_GROUP << 16,
> >  	Q2_KEY			= KEY_KEY << 16,
> > +	Q2_PATHLIST		= KEY_PATHLIST << 16,
> >  
> >  	/* byte 3: qualifier 3 */
> >  	Q3_FMT			= KEY_FMT << 24,
> > diff --git a/multipathd/cli_handlers.c b/multipathd/cli_handlers.c
> > index 2812d01e..5770dcec 100644
> > --- a/multipathd/cli_handlers.c
> > +++ b/multipathd/cli_handlers.c
> > @@ -31,6 +31,7 @@
> >  #include "foreign.h"
> >  #include "strbuf.h"
> >  #include "cli_handlers.h"
> > +#include <ctype.h>
> >  
> >  static struct path *
> >  find_path_by_str(const struct vector_s *pathvec, const char *str,
> > @@ -1276,8 +1277,8 @@ cli_getprstatus (void * v, struct strbuf
> > *reply, void * data)
> >  	return 0;
> >  }
> >  
> > -static int
> > -cli_setprstatus(void * v, struct strbuf *reply, void * data)
> > +static int do_setprstatus(void * v, struct strbuf *reply, void *
> > data,
> > +			  const struct vector_s *registered_paths)
> >  {
> >  	struct multipath * mpp;
> >  	struct vectors * vecs = (struct vectors *)data;
> > @@ -1291,7 +1292,7 @@ cli_setprstatus(void * v, struct strbuf *reply,
> > void * data)
> >  
> >  	if (mpp->prflag != PR_SET) {
> >  		set_pr(mpp);
> > -		pr_register_active_paths(mpp, true);
> > +		pr_register_active_paths(mpp, registered_paths);
> >  		if (mpp->prflag == PR_SET)
> >  			condlog(2, "%s: prflag set", param);
> >  		else
> > @@ -1302,6 +1303,38 @@ cli_setprstatus(void * v, struct strbuf
> > *reply, void * data)
> >  	return 0;
> >  }
> >  
> > +static int
> > +cli_setprstatus(void * v, struct strbuf *reply, void * data)
> > +{
> > +	return do_setprstatus(v, reply, data, NULL);
> > +}
> > +
> > +static int
> > +cli_setprstatus_list(void * v, struct strbuf *reply, void * data)
> > +{
> > +	int r;
> > +	struct vector_s registered_paths = { .allocated = 0 };
> > +	char *ptr = get_keyparam(v, KEY_PATHLIST);
> > +
> > +	while (isspace(*ptr))
> > +		ptr++;
> > +	while (*ptr) {
> > +		if (!vector_alloc_slot(&registered_paths)) {
> > +			r = -ENOMEM;
> > +			goto out;
> > +		}
> > +		vector_set_slot(&registered_paths, ptr);
> > +		while (*ptr && !isspace(*ptr))
> > +			ptr++;
> > +		while (isspace(*ptr))
> > +			*ptr++ = '\0';
> > +	}
> > +	r = do_setprstatus(v, reply, data, &registered_paths);
> > +out:
> > +	vector_reset(&registered_paths);
> > +	return r;
> > +}
> > +
> >  static int
> >  cli_unsetprstatus(void * v, struct strbuf *reply, void * data)
> >  {
> > diff --git a/multipathd/main.c b/multipathd/main.c
> > index a7650639..f00444b4 100644
> > --- a/multipathd/main.c
> > +++ b/multipathd/main.c
> > @@ -630,28 +630,50 @@ flush_map_nopaths(struct multipath *mpp, struct
> > vectors *vecs) {
> >  	return true;
> >  }
> >  
> > -void pr_register_active_paths(struct multipath *mpp, bool
> > check_nr_active)
> > +/*
> > + * If reg_paths in non-NULL, it is a vector of paths that
> > libmpathpersist
> > + * registered. If the number of registered keys is smaller than the
> > number
> > + * of registered paths, then likely a preempt that occurred while
> > + * libmpathpersist was registering the key. As long as there are
> > still some
> > + * registered keys, treat the preempt as happening first, and make
> > sure to
> > + * register keys on all the paths. If the number of registered keys
> > is at
> > + * least as large as the number of registered paths, then no preempt
> > happened,
> > + * and multipathd does not need to re-register the paths that
> > libmpathpersist
> > + * handled
> > + */
> > +void pr_register_active_paths(struct multipath *mpp,
> > +			      const struct vector_s *reg_paths)
> >  {
> > -	unsigned int i, j, nr_keys = 0;
> > -	unsigned int nr_active = 0;
> > +	unsigned int i, j, k, nr_keys = 0;
> > +	unsigned int wanted_nr = VECTOR_SIZE(reg_paths);
> >  	struct path *pp;
> >  	struct pathgroup *pgp;
> > -
> > -	if (check_nr_active) {
> > -		nr_active = count_active_paths(mpp);
> > -		if (!nr_active)
> > -			return;
> > -	}
> > +	char *pathname;
> >  
> >  	vector_foreach_slot (mpp->pg, pgp, i) {
> >  		vector_foreach_slot (pgp->paths, pp, j) {
> >  			if (mpp->prflag == PR_UNSET)
> >  				return;
> > -			if (pp->state == PATH_UP || pp->state ==
> > PATH_GHOST) {
> > -				nr_keys = mpath_pr_event_handle(pp,
> > nr_keys, nr_active);
> > -				if (check_nr_active && nr_keys ==
> > nr_active)
> > -					return;
> > +			if (pp->state != PATH_UP && pp->state !=
> > PATH_GHOST)
> > +				continue;
> > +			if (wanted_nr && nr_keys) {
> > +				vector_foreach_slot(reg_paths,
> > pathname, k) {
> > +					if (strcmp(pp->dev,
> > pathname) == 0 ||
> > +					    strcmp(pp->dev_t,
> > pathname) == 0) {
> 
> As this command is not likely to be sent by human users, do we need to
> accept both dev and dev_t here?

Probably not. I can make it just use dev_t.

-Ben
 
> > +						goto skip;
> > +					}
> > +				}
> > +			}
> > +			nr_keys = mpath_pr_event_handle(pp, nr_keys,
> > wanted_nr);
> > +			if (nr_keys && nr_keys < wanted_nr) {
> > +				/*
> > +				 * Incorrect number of registered
> > keys. Need
> > +				 * to register all devices
> > +				 */
> > +				wanted_nr = 0;
> >  			}
> > +skip:
> > +			; /* a statement must follow a label on pre
> > C23 clang */
> >  		}
> >  	}
> >  }
> > @@ -739,7 +761,7 @@ fail:
> >  
> >  	sync_map_state(mpp, false);
> >  
> > -	pr_register_active_paths(mpp, false);
> > +	pr_register_active_paths(mpp, NULL);
> >  
> >  	if (VECTOR_SIZE(offline_paths) != 0)
> >  		handle_orphaned_offline_paths(offline_paths);
> > @@ -1413,7 +1435,7 @@ rescan:
> >  
> >  	if (retries >= 0) {
> >  		if ((mpp->prflag == PR_SET && prflag != PR_SET) ||
> > start_waiter)
> > -			pr_register_active_paths(mpp, false);
> > +			pr_register_active_paths(mpp, NULL);
> >  		condlog(2, "%s [%s]: path added to devmap %s",
> >  			pp->dev, pp->dev_t, mpp->alias);
> >  		return 0;
> > @@ -2658,7 +2680,7 @@ update_path_state (struct vectors * vecs,
> > struct path * pp)
> >  				"reservation registration", pp-
> > >dev);
> >  			mpath_pr_event_handle(pp, 0, 0);
> >  			if (pp->mpp->prflag == PR_SET && prflag !=
> > PR_SET)
> > -				pr_register_active_paths(pp->mpp,
> > false);
> > +				pr_register_active_paths(pp->mpp,
> > NULL);
> >  		}
> >  
> >  		/*
> > @@ -3319,7 +3341,7 @@ configure (struct vectors * vecs, enum
> > force_reload_types reload_type)
> >  	vector_foreach_slot(mpvec, mpp, i){
> >  		if (remember_wwid(mpp->wwid) == 1)
> >  			trigger_paths_udev_change(mpp, true);
> > -		pr_register_active_paths(mpp, false);
> > +		pr_register_active_paths(mpp, NULL);
> >  	}
> >  
> >  	/*
> > @@ -4370,8 +4392,8 @@ static int update_map_pr(struct multipath *mpp,
> > struct path *pp, unsigned int *n
> >   *
> >   * nr_keys_wanted: Only used if nr_keys_needed is 0, so we don't
> > know how
> >   * many keys we currently have. If nr_keys_wanted in non-zero and
> > the
> > - * number of keys found by the initial call to update_map_pr()
> > matches it,
> > - * exit early, since we have all the keys we are expecting.
> > + * number of keys found by the initial call to update_map_pr() is at
> > least
> > + * as large as it, exit early, since we have all the keys we are
> > expecting.
> >   *
> >   * The function returns the number of keys that are registered or 0
> > if
> >   * it's unknown.
> > @@ -4394,7 +4416,7 @@ mpath_pr_event_handle(struct path *pp, unsigned
> > int nr_keys_needed,
> >  		nr_keys_needed = 1;
> >  		if (update_map_pr(mpp, pp, &nr_keys_needed) !=
> > MPATH_PR_SUCCESS)
> >  			return 0;
> > -		if (nr_keys_wanted && nr_keys_wanted ==
> > nr_keys_needed)
> > +		if (nr_keys_wanted && nr_keys_wanted <=
> > nr_keys_needed)
> >  			return nr_keys_needed;
> >  	}
> >  
> > diff --git a/multipathd/main.h b/multipathd/main.h
> > index 6d60ee81..85b533cd 100644
> > --- a/multipathd/main.h
> > +++ b/multipathd/main.h
> > @@ -54,5 +54,6 @@ int resize_map(struct multipath *mpp, unsigned long
> > long size,
> >  	       struct vectors *vecs);
> >  void set_pr(struct multipath *mpp);
> >  void unset_pr(struct multipath *mpp);
> > -void pr_register_active_paths(struct multipath *mpp, bool
> > check_active_nr);
> > +void pr_register_active_paths(struct multipath *mpp,
> > +			      const struct vector_s
> > *registered_paths);
> >  #endif /* MAIN_H_INCLUDED */
> > diff --git a/multipathd/multipathd.8.in b/multipathd/multipathd.8.in
> > index 7ffb8d4c..38a243e3 100644
> > --- a/multipathd/multipathd.8.in
> > +++ b/multipathd/multipathd.8.in
> > @@ -348,6 +348,12 @@ Restores configured queue_without_daemon mode.
> >  Enable persistent reservation management on $map.
> >  .
> >  .TP
> > +.B setprstatus map|multipath $map pathlist $pathlist
> > +Enable persistent reservation management on $map, and notify
> > multipathd of
> > +the paths that have been registered, so it doesn't attempt to re-
> > register
> > +them.
> > +.
> > +.TP
> >  .B unsetprstatus map|multipath $map
> >  Disable persistent reservation management on $map.
> >  .