Re: [dm-devel] [PATCH v5 18/22] multipath -u: quick check if path is multipathed

[Hannes Reinecke]

On Sat, 14 Apr 2018 00:00:11 +0200
Martin Wilck  wrote:

> With "find_multipaths smart", we accept paths as valid if they are
> already part of a multipath map. This patch avoids doing a full path
> and device-mapper map scan for this case, speeding up "multipath -u"
> considerably.
> 
> Signed-off-by: Martin Wilck 
> Reviewed-by: Benjamin Marzinski 
> ---
>  libmultipath/sysfs.c | 66
> 
> libmultipath/sysfs.h |  2 ++ multipath/main.c |  9 +++
>  3 files changed, 77 insertions(+)
> 
Reviewed-by: Hannes Reinecke 

Cheers,

Hannes

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[dm-devel] [PATCH v5 18/22] multipath -u: quick check if path is multipathed

[Martin Wilck]

With "find_multipaths smart", we accept paths as valid if they are
already part of a multipath map. This patch avoids doing a full path
and device-mapper map scan for this case, speeding up "multipath -u"
considerably.

Signed-off-by: Martin Wilck 
Reviewed-by: Benjamin Marzinski 
---
 libmultipath/sysfs.c | 66 
 libmultipath/sysfs.h |  2 ++
 multipath/main.c |  9 +++
 3 files changed, 77 insertions(+)

diff --git a/libmultipath/sysfs.c b/libmultipath/sysfs.c
index 97e09977..ee72e6a3 100644
--- a/libmultipath/sysfs.c
+++ b/libmultipath/sysfs.c
@@ -27,6 +27,7 @@
 #include 
 #include 
 #include 
+#include 
 
 #include "checkers.h"
 #include "vector.h"
@@ -287,3 +288,68 @@ int sysfs_check_holders(char * check_devt, char * new_devt)
 
return 0;
 }
+
+static int select_dm_devs(const struct dirent *di)
+{
+   return fnmatch("dm-*", di->d_name, FNM_FILE_NAME) == 0;
+}
+
+static void close_fd(void *arg)
+{
+   close((long)arg);
+}
+
+bool sysfs_is_multipathed(const struct path *pp)
+{
+   char pathbuf[PATH_MAX];
+   struct dirent **di;
+   int n, r, i;
+   bool found = false;
+
+   n = snprintf(pathbuf, sizeof(pathbuf), "/sys/block/%s/holders",
+pp->dev);
+
+   if (n >= sizeof(pathbuf)) {
+   condlog(1, "%s: pathname overflow", __func__);
+   return false;
+   }
+
+   r = scandir(pathbuf, , select_dm_devs, alphasort);
+   if (r == 0)
+   return false;
+   else if (r < 0) {
+   condlog(1, "%s: error scanning %s", __func__, pathbuf);
+   return false;
+   }
+
+   pthread_cleanup_push(free, di);
+   for (i = 0; i < r && !found; i++) {
+   long fd;
+   int nr;
+   char uuid[6];
+
+   if (snprintf(pathbuf + n, sizeof(pathbuf) - n,
+"/%s/dm/uuid", di[i]->d_name)
+   >= sizeof(pathbuf) - n)
+   continue;
+
+   fd = open(pathbuf, O_RDONLY);
+   if (fd == -1) {
+   condlog(1, "%s: error opening %s", __func__, pathbuf);
+   continue;
+   }
+
+   pthread_cleanup_push(close_fd, (void *)fd);
+   nr = read(fd, uuid, sizeof(uuid));
+   if (nr == sizeof(uuid) && !memcmp(uuid, "mpath-", sizeof(uuid)))
+   found = true;
+   else if (nr < 0) {
+   condlog(1, "%s: error reading from %s: %s",
+   __func__, pathbuf, strerror(errno));
+   }
+   pthread_cleanup_pop(1);
+   }
+   pthread_cleanup_pop(1);
+
+   return found;
+}
diff --git a/libmultipath/sysfs.h b/libmultipath/sysfs.h
index 75c0f9c1..9ae30b39 100644
--- a/libmultipath/sysfs.h
+++ b/libmultipath/sysfs.h
@@ -4,6 +4,7 @@
 
 #ifndef _LIBMULTIPATH_SYSFS_H
 #define _LIBMULTIPATH_SYSFS_H
+#include 
 
 ssize_t sysfs_attr_set_value(struct udev_device *dev, const char *attr_name,
 const char * value, size_t value_len);
@@ -13,4 +14,5 @@ ssize_t sysfs_bin_attr_get_value(struct udev_device *dev, 
const char *attr_name,
 unsigned char * value, size_t value_len);
 int sysfs_get_size (struct path *pp, unsigned long long * size);
 int sysfs_check_holders(char * check_devt, char * new_devt);
+bool sysfs_is_multipathed(const struct path *pp);
 #endif
diff --git a/multipath/main.c b/multipath/main.c
index 61ba90a6..96e37a7a 100644
--- a/multipath/main.c
+++ b/multipath/main.c
@@ -593,6 +593,15 @@ configure (struct config *conf, enum mpath_cmds cmd,
if (!ignore_wwids_on(conf))
goto print_valid;
/* At this point, either r==0 or find_multipaths_on. */
+
+   /*
+* Shortcut for find_multipaths smart:
+* Quick check if path is already multipathed.
+*/
+   if (sysfs_is_multipathed(VECTOR_SLOT(pathvec, 0))) {
+   r = 0;
+   goto print_valid;
+   }
if (r == 0)
goto print_valid;
/* find_multipaths_on: Fall through to path detection */
-- 
2.16.1

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