[dm-devel] [PATCH v5 09/22] libmultipath: functions to indicate mapping failure in /dev/shm

[Martin Wilck]

Create a simple API that indicates failure to create a map for a
certain WWID. This will allow multipathd to indicate to other tools
(in particular, "multipath -u" during udev processing) that
an attempt to create a map for a certain wwid failed.

The indicator is simply the existence of a file under
/dev/shm/multipath/failed_wwids. This has been chosen because it
"survives" during pivot-root between initrd and root file system.

The exact semantics of /dev/shm/multipath/failed_wwids/$WWID is:
"multipath or multipathd has tried to create this map from its
members with a DM_DEVICE_CREATE call, and failed on the latest,
or only, attempt to do so".

In particular, the existence of the file proves that here was at
least one unsuccessful attempt to create the map since the last
reboot. On the contrary, the non-existence of this file does not
indicate a successful attempt - perhaps multipathd never tried to
set up the map.

Signed-off-by: Martin Wilck <mwilck at suse.com>
Reviewed-by: Benjamin Marzinski <bmarzins at redhat.com>
---
 libmultipath/defaults.h |   1 +
 libmultipath/wwids.c    | 110 ++++++++++++++++++++++++++++++++++++++++++++++++
 libmultipath/wwids.h    |  11 +++++
 3 files changed, 122 insertions(+)

diff --git a/libmultipath/defaults.h b/libmultipath/defaults.h
index 690182c3..19ad2bfc 100644
--- a/libmultipath/defaults.h
+++ b/libmultipath/defaults.h
@@ -53,5 +53,6 @@
 #define DEFAULT_WWIDS_FILE	"/etc/multipath/wwids"
 #define DEFAULT_PRKEYS_FILE    "/etc/multipath/prkeys"
 #define DEFAULT_CONFIG_DIR	"/etc/multipath/conf.d"
+#define MULTIPATH_SHM_BASE	"/dev/shm/multipath/"
 
 char * set_default (char * str);
diff --git a/libmultipath/wwids.c b/libmultipath/wwids.c
index 5e9596fe..53e79511 100644
--- a/libmultipath/wwids.c
+++ b/libmultipath/wwids.c
@@ -5,6 +5,7 @@
 #include <limits.h>
 #include <stdio.h>
 #include <sys/types.h>
+#include <sys/stat.h>
 
 #include "checkers.h"
 #include "vector.h"
@@ -333,3 +334,112 @@ remember_wwid(char *wwid)
 		condlog(4, "wwid %s already in wwids file", wwid);
 	return ret;
 }
+
+static const char shm_dir[] = MULTIPATH_SHM_BASE "failed_wwids";
+static const char shm_lock[] = ".lock";
+static const char shm_header[] = "multipath shm lock file, don't edit";
+static char _shm_lock_path[sizeof(shm_dir)+sizeof(shm_lock)];
+static const char *shm_lock_path = &_shm_lock_path[0];
+
+static void init_shm_paths(void)
+{
+	snprintf(_shm_lock_path, sizeof(_shm_lock_path),
+		 "%s/%s", shm_dir, shm_lock);
+}
+
+static pthread_once_t shm_path_once = PTHREAD_ONCE_INIT;
+
+static int multipath_shm_open(bool rw)
+{
+	int fd;
+	int can_write;
+
+	pthread_once(&shm_path_once, init_shm_paths);
+	fd = open_file(shm_lock_path, &can_write, shm_header);
+
+	if (fd >= 0 && rw && !can_write) {
+		close(fd);
+		condlog(1, "failed to open %s for writing", shm_dir);
+		return -1;
+	}
+
+	return fd;
+}
+
+static void multipath_shm_close(void *arg)
+{
+	long fd = (long)arg;
+
+	close(fd);
+	unlink(shm_lock_path);
+}
+
+static int _failed_wwid_op(const char *wwid, bool rw,
+			   int (*func)(const char *), const char *msg)
+{
+	char path[PATH_MAX];
+	long lockfd;
+	int r = -1;
+
+	if (snprintf(path, sizeof(path), "%s/%s", shm_dir, wwid)
+	    >= sizeof(path)) {
+		condlog(1, "%s: path name overflow", __func__);
+		return -1;
+	}
+
+	lockfd = multipath_shm_open(rw);
+	if (lockfd == -1)
+		return -1;
+
+	pthread_cleanup_push(multipath_shm_close, (void *)lockfd);
+	r = func(path);
+	pthread_cleanup_pop(1);
+
+	if (r == WWID_FAILED_ERROR)
+		condlog(1, "%s: %s: %s", msg, wwid, strerror(errno));
+	else if (r == WWID_FAILED_CHANGED)
+		condlog(3, "%s: %s", msg, wwid);
+	else if (!rw)
+		condlog(4, "%s: %s is %s", msg, wwid,
+			r == WWID_IS_FAILED ? "failed" : "good");
+
+	return r;
+}
+
+static int _is_failed(const char *path)
+{
+	struct stat st;
+
+	if (lstat(path, &st) == 0)
+		return WWID_IS_FAILED;
+	else if (errno == ENOENT)
+		return WWID_IS_NOT_FAILED;
+	else
+		return WWID_FAILED_ERROR;
+}
+
+static int _mark_failed(const char *path)
+{
+	/* Called from _failed_wwid_op: we know that shm_lock_path exists */
+	if (_is_failed(path) == WWID_IS_FAILED)
+		return WWID_FAILED_UNCHANGED;
+	return (link(shm_lock_path, path) == 0 ? WWID_FAILED_CHANGED :
+		WWID_FAILED_ERROR);
+}
+
+static int _unmark_failed(const char *path)
+{
+	if (_is_failed(path) == WWID_IS_NOT_FAILED)
+		return WWID_FAILED_UNCHANGED;
+	return (unlink(path) == 0 ? WWID_FAILED_CHANGED : WWID_FAILED_ERROR);
+}
+
+#define declare_failed_wwid_op(op, rw) \
+int op ## _wwid(const char *wwid) \
+{ \
+	return _failed_wwid_op(wwid, (rw), _ ## op, #op); \
+}
+
+declare_failed_wwid_op(is_failed, false)
+declare_failed_wwid_op(mark_failed, true)
+declare_failed_wwid_op(unmark_failed, true)
diff --git a/libmultipath/wwids.h b/libmultipath/wwids.h
index d9a78b38..0c6ee54d 100644
--- a/libmultipath/wwids.h
+++ b/libmultipath/wwids.h
@@ -18,4 +18,15 @@ int check_wwids_file(char *wwid, int write_wwid);
 int remove_wwid(char *wwid);
 int replace_wwids(vector mp);
 
+enum {
+	WWID_IS_NOT_FAILED = 0,
+	WWID_IS_FAILED,
+	WWID_FAILED_UNCHANGED,
+	WWID_FAILED_CHANGED,
+	WWID_FAILED_ERROR = -1,
+};
+
+int is_failed_wwid(const char *wwid);
+int mark_failed_wwid(const char *wwid);
+int unmark_failed_wwid(const char *wwid);
 #endif /* _WWIDS_H */
-- 
2.16.1