[PATCH 0/2] multipath-tools: Add option to disable NVMe ("foreign") support

[PATCH 0/2] multipath-tools: Add option to disable NVMe ("foreign") support

[Martin Wilck]

From: Martin Wilck <mwilck@suse.com>

Hi Christophe, hi Ben,

This is my alternative take to Ben's "multipath: add print_foreign option"
patch. I'd prefer it because it's more generic and more flexible for future
extensions.

Regards
Martin

Martin Wilck (2):
  multipath.conf: add "enable_foreign" parameter
  multipath.conf.5: document foreign library support

 libmultipath/config.h      |  1 +
 libmultipath/defaults.h    |  2 ++
 libmultipath/dict.c        |  6 +++++
 libmultipath/foreign.c     | 53 +++++++++++++++++++++++++++++++++++---
 libmultipath/foreign.h     |  3 ++-
 multipath/main.c           |  2 +-
 multipath/multipath.conf.5 | 40 ++++++++++++++++++++++++++++
 multipathd/main.c          |  2 +-
 8 files changed, 102 insertions(+), 7 deletions(-)

-- 
2.22.0

[PATCH 1/2] multipath.conf: add "enable_foreign" parameter

[Martin Wilck]

From: Martin Wilck <mwilck@suse.com>

This new configuration parameter can be used to selectively
enable foreign libraries. The value is a regular expression,
against which foreign library names such as "nvme" are matched.
By setting this to a value that matches no foreign library
(e.g. "^$" or "NONE"), foreign code is completely disabled.
By default, all available foreign libraries are loaded.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
 libmultipath/config.h   |  1 +
 libmultipath/defaults.h |  2 ++
 libmultipath/dict.c     |  6 +++++
 libmultipath/foreign.c  | 53 +++++++++++++++++++++++++++++++++++++----
 libmultipath/foreign.h  |  3 ++-
 multipath/main.c        |  2 +-
 multipathd/main.c       |  2 +-
 7 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/libmultipath/config.h b/libmultipath/config.h
index ff2b4e86..36e99196 100644
--- a/libmultipath/config.h
+++ b/libmultipath/config.h
@@ -224,6 +224,7 @@ struct config {
 	vector elist_device;
 	vector elist_property;
 	vector elist_protocol;
+	char *enable_foreign;
 };
 
 extern struct udev * udev;
diff --git a/libmultipath/defaults.h b/libmultipath/defaults.h
index decc9335..4dfe007c 100644
--- a/libmultipath/defaults.h
+++ b/libmultipath/defaults.h
@@ -48,6 +48,8 @@
 #define DEFAULT_FIND_MULTIPATHS_TIMEOUT -10
 #define DEFAULT_UNKNOWN_FIND_MULTIPATHS_TIMEOUT 1
 #define DEFAULT_ALL_TG_PT ALL_TG_PT_OFF
+/* Enable all foreign libraries by default */
+#define DEFAULT_ENABLE_FOREIGN ""
 
 #define CHECKINT_UNDEF		(~0U)
 #define DEFAULT_CHECKINT	5
diff --git a/libmultipath/dict.c b/libmultipath/dict.c
index c6eba0f6..9f282c3f 100644
--- a/libmultipath/dict.c
+++ b/libmultipath/dict.c
@@ -610,6 +610,10 @@ declare_def_handler(find_multipaths_timeout, set_int)
 declare_def_snprint_defint(find_multipaths_timeout, print_int,
 			   DEFAULT_FIND_MULTIPATHS_TIMEOUT)
 
+declare_def_handler(enable_foreign, set_str)
+declare_def_snprint_defstr(enable_foreign, print_str,
+			   DEFAULT_ENABLE_FOREIGN)
+
 static int
 def_config_dir_handler(struct config *conf, vector strvec)
 {
@@ -1710,6 +1714,8 @@ init_keywords(vector keywords)
 	install_keyword("find_multipaths_timeout",
 			&def_find_multipaths_timeout_handler,
 			&snprint_def_find_multipaths_timeout);
+	install_keyword("enable_foreign", &def_enable_foreign_handler,
+			&snprint_def_enable_foreign);
 	__deprecated install_keyword("default_selector", &def_selector_handler, NULL);
 	__deprecated install_keyword("default_path_grouping_policy", &def_pgpolicy_handler, NULL);
 	__deprecated install_keyword("default_uid_attribute", &def_uid_attribute_handler, NULL);
diff --git a/libmultipath/foreign.c b/libmultipath/foreign.c
index 48e8d247..4b34e141 100644
--- a/libmultipath/foreign.c
+++ b/libmultipath/foreign.c
@@ -16,6 +16,7 @@
 */
 
 #include <sys/sysmacros.h>
+#include <sys/types.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -25,6 +26,7 @@
 #include <fnmatch.h>
 #include <dlfcn.h>
 #include <libudev.h>
+#include <regex.h>
 #include "vector.h"
 #include "debug.h"
 #include "util.h"
@@ -111,17 +113,45 @@ static int select_foreign_libs(const struct dirent *di)
 	return fnmatch(foreign_pattern, di->d_name, FNM_FILE_NAME) == 0;
 }
 
-static int _init_foreign(const char *multipath_dir)
+static void free_pre(void *arg)
+{
+	regex_t **pre = arg;
+
+	if (pre != NULL && *pre != NULL) {
+		regfree(*pre);
+		free(*pre);
+		*pre = NULL;
+	}
+}
+
+static int _init_foreign(const char *multipath_dir, const char *enable)
 {
 	char pathbuf[PATH_MAX];
 	struct dirent **di;
 	struct scandir_result sr;
 	int r, i;
+	regex_t *enable_re = NULL;
 
 	foreigns = vector_alloc();
 	if (foreigns == NULL)
 		return -ENOMEM;
 
+	pthread_cleanup_push(free_pre, &enable_re);
+	enable_re = calloc(1, sizeof(*enable_re));
+	if (enable_re) {
+		const char *str = enable ? enable : DEFAULT_ENABLE_FOREIGN;
+
+		r = regcomp(enable_re, str, REG_EXTENDED|REG_NOSUB);
+		if (r != 0) {
+			char errbuf[64];
+
+			(void)regerror(r, enable_re, errbuf, sizeof(errbuf));
+			condlog (2, "%s: error compiling enable_foreign = \"%s\": \"%s\"",
+				 __func__, str, errbuf);
+			free_pre(&enable_re);
+		}
+	}
+
 	r = scandir(multipath_dir, &di, select_foreign_libs, alphasort);
 
 	if (r == 0) {
@@ -163,6 +193,20 @@ static int _init_foreign(const char *multipath_dir)
 		memset(fgn, 0, sizeof(*fgn));
 		strlcpy((char*)fgn + offsetof(struct foreign, name), c, namesz);
 
+		if (enable_re != NULL) {
+			int ret = regexec(enable_re, fgn->name, 0, NULL, 0);
+
+			if (ret == REG_NOMATCH) {
+				condlog(3, "%s: foreign library \"%s\" is not enabled",
+					__func__, fgn->name);
+				free(fgn);
+				continue;
+			} else if (ret != 0)
+				/* assume it matches */
+				condlog(2, "%s: error %d in regexec() for %s",
+					__func__, ret, fgn->name);
+		}
+
 		snprintf(pathbuf, sizeof(pathbuf), "%s/%s", multipath_dir, fn);
 		fgn->handle = dlopen(pathbuf, RTLD_NOW|RTLD_LOCAL);
 		msg = dlerror();
@@ -205,11 +249,12 @@ static int _init_foreign(const char *multipath_dir)
 	dl_err:
 		free_foreign(fgn);
 	}
-	pthread_cleanup_pop(1);
+	pthread_cleanup_pop(1); /* free_scandir_result */
+	pthread_cleanup_pop(1); /* free_pre */
 	return 0;
 }
 
-int init_foreign(const char *multipath_dir)
+int init_foreign(const char *multipath_dir, const char *enable)
 {
 	int ret;
 
@@ -222,7 +267,7 @@ int init_foreign(const char *multipath_dir)
 	}
 
 	pthread_cleanup_push(unlock_foreigns, NULL);
-	ret = _init_foreign(multipath_dir);
+	ret = _init_foreign(multipath_dir, enable);
 	pthread_cleanup_pop(1);
 
 	return ret;
diff --git a/libmultipath/foreign.h b/libmultipath/foreign.h
index 697f12f8..acd33601 100644
--- a/libmultipath/foreign.h
+++ b/libmultipath/foreign.h
@@ -195,9 +195,10 @@ struct foreign {
  * init_foreign(dir)
  * load and initialize foreign multipath libraries in dir (libforeign-*.so).
  * @param dir: directory to search
+ * @param enable: regex to match foreign library name ("*" above) against
  * @returns: 0 on success, negative value on failure.
  */
-int init_foreign(const char *multipath_dir);
+int init_foreign(const char *multipath_dir, const char *enable);
 
 /**
  * cleanup_foreign(dir)
diff --git a/multipath/main.c b/multipath/main.c
index 96a11468..4f4d8e89 100644
--- a/multipath/main.c
+++ b/multipath/main.c
@@ -1050,7 +1050,7 @@ main (int argc, char *argv[])
 		goto out;
 	}
 	/* Failing here is non-fatal */
-	init_foreign(conf->multipath_dir);
+	init_foreign(conf->multipath_dir, conf->enable_foreign);
 	if (cmd == CMD_USABLE_PATHS) {
 		r = check_usable_paths(conf, dev, dev_type) ?
 			RTVL_FAIL : RTVL_OK;
diff --git a/multipathd/main.c b/multipathd/main.c
index 7a5cd115..b5f08617 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -2848,7 +2848,7 @@ child (void * param)
 	}
 	/* Failing this is non-fatal */
 
-	init_foreign(conf->multipath_dir);
+	init_foreign(conf->multipath_dir, conf->enable_foreign);
 
 	if (poll_dmevents)
 		poll_dmevents = dmevent_poll_supported();
-- 
2.22.0

Re: [PATCH 1/2] multipath.conf: add "enable_foreign" parameter

[Benjamin Marzinski]

On Thu, Aug 15, 2019 at 02:46:54PM +0000, Martin Wilck wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> This new configuration parameter can be used to selectively
> enable foreign libraries. The value is a regular expression,
> against which foreign library names such as "nvme" are matched.
> By setting this to a value that matches no foreign library
> (e.g. "^$" or "NONE"), foreign code is completely disabled.
> By default, all available foreign libraries are loaded.
> 

This will stop the foreign libraries from even claiming devices. Won't
this mean that pathinfo() will now treat these devices as multipathable
paths, since is_claimed_by_foreign() will return false? While I do see
the value in disabling foreign libraries completely, that's not the
intent of my patch.  The goal of my patch is simply to not print the
devices have been claimed by the foreign libraries.

-Ben

> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmultipath/config.h   |  1 +
>  libmultipath/defaults.h |  2 ++
>  libmultipath/dict.c     |  6 +++++
>  libmultipath/foreign.c  | 53 +++++++++++++++++++++++++++++++++++++----
>  libmultipath/foreign.h  |  3 ++-
>  multipath/main.c        |  2 +-
>  multipathd/main.c       |  2 +-
>  7 files changed, 62 insertions(+), 7 deletions(-)
> 
> diff --git a/libmultipath/config.h b/libmultipath/config.h
> index ff2b4e86..36e99196 100644
> --- a/libmultipath/config.h
> +++ b/libmultipath/config.h
> @@ -224,6 +224,7 @@ struct config {
>  	vector elist_device;
>  	vector elist_property;
>  	vector elist_protocol;
> +	char *enable_foreign;
>  };
>  
>  extern struct udev * udev;
> diff --git a/libmultipath/defaults.h b/libmultipath/defaults.h
> index decc9335..4dfe007c 100644
> --- a/libmultipath/defaults.h
> +++ b/libmultipath/defaults.h
> @@ -48,6 +48,8 @@
>  #define DEFAULT_FIND_MULTIPATHS_TIMEOUT -10
>  #define DEFAULT_UNKNOWN_FIND_MULTIPATHS_TIMEOUT 1
>  #define DEFAULT_ALL_TG_PT ALL_TG_PT_OFF
> +/* Enable all foreign libraries by default */
> +#define DEFAULT_ENABLE_FOREIGN ""
>  
>  #define CHECKINT_UNDEF		(~0U)
>  #define DEFAULT_CHECKINT	5
> diff --git a/libmultipath/dict.c b/libmultipath/dict.c
> index c6eba0f6..9f282c3f 100644
> --- a/libmultipath/dict.c
> +++ b/libmultipath/dict.c
> @@ -610,6 +610,10 @@ declare_def_handler(find_multipaths_timeout, set_int)
>  declare_def_snprint_defint(find_multipaths_timeout, print_int,
>  			   DEFAULT_FIND_MULTIPATHS_TIMEOUT)
>  
> +declare_def_handler(enable_foreign, set_str)
> +declare_def_snprint_defstr(enable_foreign, print_str,
> +			   DEFAULT_ENABLE_FOREIGN)
> +
>  static int
>  def_config_dir_handler(struct config *conf, vector strvec)
>  {
> @@ -1710,6 +1714,8 @@ init_keywords(vector keywords)
>  	install_keyword("find_multipaths_timeout",
>  			&def_find_multipaths_timeout_handler,
>  			&snprint_def_find_multipaths_timeout);
> +	install_keyword("enable_foreign", &def_enable_foreign_handler,
> +			&snprint_def_enable_foreign);
>  	__deprecated install_keyword("default_selector", &def_selector_handler, NULL);
>  	__deprecated install_keyword("default_path_grouping_policy", &def_pgpolicy_handler, NULL);
>  	__deprecated install_keyword("default_uid_attribute", &def_uid_attribute_handler, NULL);
> diff --git a/libmultipath/foreign.c b/libmultipath/foreign.c
> index 48e8d247..4b34e141 100644
> --- a/libmultipath/foreign.c
> +++ b/libmultipath/foreign.c
> @@ -16,6 +16,7 @@
>  */
>  
>  #include <sys/sysmacros.h>
> +#include <sys/types.h>
>  #include <stdio.h>
>  #include <string.h>
>  #include <stdlib.h>
> @@ -25,6 +26,7 @@
>  #include <fnmatch.h>
>  #include <dlfcn.h>
>  #include <libudev.h>
> +#include <regex.h>
>  #include "vector.h"
>  #include "debug.h"
>  #include "util.h"
> @@ -111,17 +113,45 @@ static int select_foreign_libs(const struct dirent *di)
>  	return fnmatch(foreign_pattern, di->d_name, FNM_FILE_NAME) == 0;
>  }
>  
> -static int _init_foreign(const char *multipath_dir)
> +static void free_pre(void *arg)
> +{
> +	regex_t **pre = arg;
> +
> +	if (pre != NULL && *pre != NULL) {
> +		regfree(*pre);
> +		free(*pre);
> +		*pre = NULL;
> +	}
> +}
> +
> +static int _init_foreign(const char *multipath_dir, const char *enable)
>  {
>  	char pathbuf[PATH_MAX];
>  	struct dirent **di;
>  	struct scandir_result sr;
>  	int r, i;
> +	regex_t *enable_re = NULL;
>  
>  	foreigns = vector_alloc();
>  	if (foreigns == NULL)
>  		return -ENOMEM;
>  
> +	pthread_cleanup_push(free_pre, &enable_re);
> +	enable_re = calloc(1, sizeof(*enable_re));
> +	if (enable_re) {
> +		const char *str = enable ? enable : DEFAULT_ENABLE_FOREIGN;
> +
> +		r = regcomp(enable_re, str, REG_EXTENDED|REG_NOSUB);
> +		if (r != 0) {
> +			char errbuf[64];
> +
> +			(void)regerror(r, enable_re, errbuf, sizeof(errbuf));
> +			condlog (2, "%s: error compiling enable_foreign = \"%s\": \"%s\"",
> +				 __func__, str, errbuf);
> +			free_pre(&enable_re);
> +		}
> +	}
> +
>  	r = scandir(multipath_dir, &di, select_foreign_libs, alphasort);
>  
>  	if (r == 0) {
> @@ -163,6 +193,20 @@ static int _init_foreign(const char *multipath_dir)
>  		memset(fgn, 0, sizeof(*fgn));
>  		strlcpy((char*)fgn + offsetof(struct foreign, name), c, namesz);
>  
> +		if (enable_re != NULL) {
> +			int ret = regexec(enable_re, fgn->name, 0, NULL, 0);
> +
> +			if (ret == REG_NOMATCH) {
> +				condlog(3, "%s: foreign library \"%s\" is not enabled",
> +					__func__, fgn->name);
> +				free(fgn);
> +				continue;
> +			} else if (ret != 0)
> +				/* assume it matches */
> +				condlog(2, "%s: error %d in regexec() for %s",
> +					__func__, ret, fgn->name);
> +		}
> +
>  		snprintf(pathbuf, sizeof(pathbuf), "%s/%s", multipath_dir, fn);
>  		fgn->handle = dlopen(pathbuf, RTLD_NOW|RTLD_LOCAL);
>  		msg = dlerror();
> @@ -205,11 +249,12 @@ static int _init_foreign(const char *multipath_dir)
>  	dl_err:
>  		free_foreign(fgn);
>  	}
> -	pthread_cleanup_pop(1);
> +	pthread_cleanup_pop(1); /* free_scandir_result */
> +	pthread_cleanup_pop(1); /* free_pre */
>  	return 0;
>  }
>  
> -int init_foreign(const char *multipath_dir)
> +int init_foreign(const char *multipath_dir, const char *enable)
>  {
>  	int ret;
>  
> @@ -222,7 +267,7 @@ int init_foreign(const char *multipath_dir)
>  	}
>  
>  	pthread_cleanup_push(unlock_foreigns, NULL);
> -	ret = _init_foreign(multipath_dir);
> +	ret = _init_foreign(multipath_dir, enable);
>  	pthread_cleanup_pop(1);
>  
>  	return ret;
> diff --git a/libmultipath/foreign.h b/libmultipath/foreign.h
> index 697f12f8..acd33601 100644
> --- a/libmultipath/foreign.h
> +++ b/libmultipath/foreign.h
> @@ -195,9 +195,10 @@ struct foreign {
>   * init_foreign(dir)
>   * load and initialize foreign multipath libraries in dir (libforeign-*.so).
>   * @param dir: directory to search
> + * @param enable: regex to match foreign library name ("*" above) against
>   * @returns: 0 on success, negative value on failure.
>   */
> -int init_foreign(const char *multipath_dir);
> +int init_foreign(const char *multipath_dir, const char *enable);
>  
>  /**
>   * cleanup_foreign(dir)
> diff --git a/multipath/main.c b/multipath/main.c
> index 96a11468..4f4d8e89 100644
> --- a/multipath/main.c
> +++ b/multipath/main.c
> @@ -1050,7 +1050,7 @@ main (int argc, char *argv[])
>  		goto out;
>  	}
>  	/* Failing here is non-fatal */
> -	init_foreign(conf->multipath_dir);
> +	init_foreign(conf->multipath_dir, conf->enable_foreign);
>  	if (cmd == CMD_USABLE_PATHS) {
>  		r = check_usable_paths(conf, dev, dev_type) ?
>  			RTVL_FAIL : RTVL_OK;
> diff --git a/multipathd/main.c b/multipathd/main.c
> index 7a5cd115..b5f08617 100644
> --- a/multipathd/main.c
> +++ b/multipathd/main.c
> @@ -2848,7 +2848,7 @@ child (void * param)
>  	}
>  	/* Failing this is non-fatal */
>  
> -	init_foreign(conf->multipath_dir);
> +	init_foreign(conf->multipath_dir, conf->enable_foreign);
>  
>  	if (poll_dmevents)
>  		poll_dmevents = dmevent_poll_supported();
> -- 
> 2.22.0

Re: [PATCH 1/2] multipath.conf: add "enable_foreign" parameter

[Martin Wilck]

On Fri, 2019-08-16 at 15:12 -0500, Benjamin Marzinski wrote:
> On Thu, Aug 15, 2019 at 02:46:54PM +0000, Martin Wilck wrote:
> > From: Martin Wilck <mwilck@suse.com>
> > 
> > This new configuration parameter can be used to selectively
> > enable foreign libraries. The value is a regular expression,
> > against which foreign library names such as "nvme" are matched.
> > By setting this to a value that matches no foreign library
> > (e.g. "^$" or "NONE"), foreign code is completely disabled.
> > By default, all available foreign libraries are loaded.
> > 
> 
> This will stop the foreign libraries from even claiming devices.
> Won't
> this mean that pathinfo() will now treat these devices as
> multipathable
> paths, since is_claimed_by_foreign() will return false? 

IMO this won't happen, because we ignore the native multipath path
devices anyway as they're "hidden", and we ignore native NVMe multipath
maps because they have "nvme-subsystem" subsystem rather than "nvme"
(commit b18ed66). But I'll double-check again.

Martin

Re: [PATCH 1/2] multipath.conf: add "enable_foreign" parameter

[Martin Wilck]

On Mon, 2019-08-19 at 20:32 +0000, Martin Wilck wrote:
> On Fri, 2019-08-16 at 15:12 -0500, Benjamin Marzinski wrote:
> > On Thu, Aug 15, 2019 at 02:46:54PM +0000, Martin Wilck wrote:
> > > From: Martin Wilck <mwilck@suse.com>
> > > 
> > > This new configuration parameter can be used to selectively
> > > enable foreign libraries. The value is a regular expression,
> > > against which foreign library names such as "nvme" are matched.
> > > By setting this to a value that matches no foreign library
> > > (e.g. "^$" or "NONE"), foreign code is completely disabled.
> > > By default, all available foreign libraries are loaded.
> > > 
> > 
> > This will stop the foreign libraries from even claiming devices.
> > Won't
> > this mean that pathinfo() will now treat these devices as
> > multipathable
> > paths, since is_claimed_by_foreign() will return false? 
> 
> IMO this won't happen, because we ignore the native multipath path
> devices anyway as they're "hidden", and we ignore native NVMe
> multipath
> maps because they have "nvme-subsystem" subsystem rather than "nvme"
> (commit b18ed66). But I'll double-check again.

Confirmed. With nvme_core.multipath=Y and the nvme library disabled,no
NVMe-related output is printed.

Ben, with that in mind, would you ACK this patch?

Martin

Re: [PATCH 1/2] multipath.conf: add "enable_foreign" parameter

[Benjamin Marzinski]

On Tue, Aug 20, 2019 at 04:24:58PM +0000, Martin Wilck wrote:
> On Mon, 2019-08-19 at 20:32 +0000, Martin Wilck wrote:
> > On Fri, 2019-08-16 at 15:12 -0500, Benjamin Marzinski wrote:
> > > On Thu, Aug 15, 2019 at 02:46:54PM +0000, Martin Wilck wrote:
> > > > From: Martin Wilck <mwilck@suse.com>
> > > > 
> > > > This new configuration parameter can be used to selectively
> > > > enable foreign libraries. The value is a regular expression,
> > > > against which foreign library names such as "nvme" are matched.
> > > > By setting this to a value that matches no foreign library
> > > > (e.g. "^$" or "NONE"), foreign code is completely disabled.
> > > > By default, all available foreign libraries are loaded.
> > > > 
> > > 
> > > This will stop the foreign libraries from even claiming devices.
> > > Won't
> > > this mean that pathinfo() will now treat these devices as
> > > multipathable
> > > paths, since is_claimed_by_foreign() will return false? 
> > 
> > IMO this won't happen, because we ignore the native multipath path
> > devices anyway as they're "hidden", and we ignore native NVMe
> > multipath
> > maps because they have "nvme-subsystem" subsystem rather than "nvme"
> > (commit b18ed66). But I'll double-check again.
> 
> Confirmed. With nvme_core.multipath=Y and the nvme library disabled,no
> NVMe-related output is printed.
> 
> Ben, with that in mind, would you ACK this patch?

Sure. Sorry about the confusion

Reviewed-by: Benjamin Marzinksi <bmarzins@redhat.com>
 
> Martin
> 

[PATCH 2/2] multipath.conf.5: document foreign library support

[Martin Wilck]

From: Martin Wilck <mwilck@suse.com>

Add documentation for foreign library support, and for the
"enable_foreign" parameter.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
 multipath/multipath.conf.5 | 40 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/multipath/multipath.conf.5 b/multipath/multipath.conf.5
index f7d21b4c..c1446231 100644
--- a/multipath/multipath.conf.5
+++ b/multipath/multipath.conf.5
@@ -1194,6 +1194,21 @@ makes multipath immediately mark a device with only ghost paths as ready.
 The default is: \fBno\fR
 .RE
 .
+.
+.TP
+.B enable_foreign
+Enables or disables foreign libraries (see section
+.I FOREIGN MULTIPATH SUPPORT
+below). The value is a regular expression; foreign libraries are loaded
+if their name (e.g. \(dqnvme\(dq) matches the expression. By default,
+all foreign libraries are enabled.
+.RS
+.TP
+The default is: \fB\(dq\(dq\fR (the empty regular expression)
+.RE
+.
+.
+
 .
 .\" ----------------------------------------------------------------------------
 .SH "blacklist and blacklist_exceptions sections"
@@ -1735,6 +1750,31 @@ unpredictable ways. If the \(dqmarginal_path\(dq method is active, the
 .
 .
 .\" ----------------------------------------------------------------------------
+.SH "FOREIGN MULTIPATH SUPPORT"
+.\" ----------------------------------------------------------------------------
+.
+multipath and multipathd can load \(dqforeign\(dq libraries to add
+support for other multipathing technologies besides the Linux device mapper.
+Currently this support is limited to printing detected information about
+multipath setup. In topology output, the names of foreign maps are prefixed by
+the foreign library name in square brackets, as in this example:
+.
+.P
+.EX
+# multipath -ll
+uuid.fedcba98-3579-4567-8765-123456789abc [nvme]:nvme4n9 NVMe,Some NVMe controller,FFFFFFFF
+size=167772160 features='n/a' hwhandler='ANA' wp=rw
+|-+- policy='n/a' prio=50 status=optimized
+| `- 4:38:1    nvme4c38n1 0:0     n/a   optimized    live
+`-+- policy='n/a' prio=50 status=optimized
+  `- 4:39:1    nvme4c39n1 0:0     n/a   optimized    live
+.EE
+.
+.P
+The \(dqnvme\(dq foreign library provides support for NVMe native multipathing
+in the kernel. It is part of the standard multipath package.
+.
+.\" ----------------------------------------------------------------------------
 .SH "KNOWN ISSUES"
 .\" ----------------------------------------------------------------------------
 .
-- 
2.22.0