libdm: Add dm_udev_wait_immediate.

dm_udev_wait() waits inside the library.
dm_udev_wait_immediate allows the caller to do other things if the
cookie isn't yet ready to be decremented.

WHATS_NEW_DM

@@ -1,5 +1,6 @@
 Version 1.02.124 - 
 ==================================
+  Add dm_udev_wait_immediate to libdevmapper for waiting outside the library.
 
 Version 1.02.123 - 23rd April 2016
 ==================================

libdm/.exported_symbols.DM_1_02_124

@@ -0,0 +1 @@
+dm_udev_wait_immediate

libdm/libdevmapper.h

@@ -3218,6 +3218,15 @@ int dm_udev_create_cookie(uint32_t *cookie);
 int dm_udev_complete(uint32_t cookie);
 int dm_udev_wait(uint32_t cookie);
 
+/*
+ * dm_dev_wait_immediate 
+ * If *ready is 1 on return, the wait is complete.
+ * If *ready is 0 on return, the wait is incomplete and either
+ * this function or dm_udev_wait() must be called again.
+ * Returns 0 on error, when neither function should be called again.
+ */
+int dm_udev_wait_immediate(uint32_t cookie, int *ready);
+
 #define DM_DEV_DIR_UMASK 0022
 #define DM_CONTROL_NODE_UMASK 0177
 

libdm/libdm-common.c

@@ -2082,6 +2082,14 @@ int dm_udev_wait(uint32_t cookie)
 	return 1;
 }
 
+int dm_udev_wait_immediate(uint32_t cookie, int *ready)
+{
+	update_devs();
+	*ready = 1;
+
+	return 1;
+}
+
 #else		/* UDEV_SYNC_SUPPORT */
 
 static int _check_semaphore_is_supported(void)
@@ -2506,10 +2514,16 @@ int dm_udev_complete(uint32_t cookie)
 	return 1;
 }
 
-static int _udev_wait(uint32_t cookie)
+/*
+ * If *nowait is set, return immediately leaving it set if the semaphore
+ * is not ready to be decremented to 0.  *nowait is cleared if the wait
+ * succeeds.
+ */
+static int _udev_wait(uint32_t cookie, int *nowait)
 {
 	int semid;
 	struct sembuf sb = {0, 0, 0};
+	int val;
 
 	if (!cookie || !dm_udev_get_sync_support())
 		return 1;
@@ -2517,6 +2531,21 @@ static int _udev_wait(uint32_t cookie)
 	if (!_get_cookie_sem(cookie, &semid))
 		return_0;
 
+	/* Return immediately if the semaphore value exceeds 1? */
+	if (*nowait) {
+		if ((val = semctl(semid, 0, GETVAL)) < 0) {
+			log_error("semid %d: sem_ctl GETVAL failed for "
+				  "cookie 0x%" PRIx32 ": %s",
+				  semid, cookie, strerror(errno));
+			return 0;		
+		}
+
+		if (val > 1)
+			return 1;
+
+		*nowait = 0;
+	}
+
 	if (!_udev_notify_sem_dec(cookie, semid)) {
 		log_error("Failed to set a proper state for notification "
 			  "semaphore identified by cookie value %" PRIu32 " (0x%x) "
@@ -2548,11 +2577,27 @@ repeat_wait:
 
 int dm_udev_wait(uint32_t cookie)
 {
-	int r = _udev_wait(cookie);
+	int nowait = 0;
+	int r = _udev_wait(cookie, &nowait);
 
 	update_devs();
 
 	return r;
 }
 
+int dm_udev_wait_immediate(uint32_t cookie, int *ready)
+{
+	int nowait = 1;
+	int r = _udev_wait(cookie, &nowait);
+
+	if (r && nowait) {
+		*ready = 0;
+		return 1;
+	}
+
+	update_devs();
+	*ready = 1;
+
+	return r;
+}
 #endif		/* UDEV_SYNC_SUPPORT */