From: Andre Noll <maan@systemlinux.org>
Date: Sat, 13 Nov 2010 19:51:28 +0000 (+0100)
Subject: Add the --kill subcommand.
X-Git-Tag: v0.1.5~13^2~2
X-Git-Url: http://git.tuebingen.mpg.de/?p=dss.git;a=commitdiff_plain;h=492928ebe8b83c31aeca4866fef37ab07174ed9c;hp=dd42f745333f7273a1ef1e81b090705473de8079

Add the --kill subcommand.

It works as follows: Whenever a semaphore operation is performed, the
PID of the process is stored in the sempid field of the semaphore.
This PID can be obtained from a different process by calling semctl
with the GETPID command.

com_kill() first tries to acquire the lock by calling the new
mutex_try_lock() function of ipc.c. In contrast to mutex_lock(),
mutex_try_lock() only operates on the first semaphore in the semaphore
set, leaving the sempid field of the second semaphore unchanged. If
mutex_try_lock() succeeds, no running dss process is holding the lock
and the kill command fails. Otherwise, some dss process is running
whose PID can be obtained by calling semctl() on the second semaphore.
---

diff --git a/dss.c b/dss.c
index 01f1bc7..63f5f56 100644
--- a/dss.c
+++ b/dss.c
@@ -171,7 +171,8 @@ static void dump_dss_config(const char *msg)
 	COMMAND(ls) \
 	COMMAND(create) \
 	COMMAND(prune) \
-	COMMAND(run)
+	COMMAND(run) \
+	COMMAND(kill)
 #define COMMAND(x) static int com_ ##x(void);
 COMMANDS
 #undef COMMAND
@@ -239,6 +240,25 @@ static char *get_config_file_name(void)
 	return config_file;
 }
 
+static int com_kill(void)
+{
+	pid_t pid;
+	char *config_file = get_config_file_name();
+	int ret = get_dss_pid(config_file, &pid);
+
+	free(config_file);
+	if (ret < 0)
+		return ret;
+	if (conf.dry_run_given) {
+		dss_msg("%d\n", (int)pid);
+		return 0;
+	}
+	ret = kill(pid, SIGTERM);
+	if (ret < 0)
+		return -ERRNO_TO_DSS_ERROR(errno);
+	return 1;
+}
+
 static void dss_get_snapshot_list(struct snapshot_list *sl)
 {
 	get_snapshot_list(sl, conf.unit_interval_arg, conf.num_intervals_arg);
diff --git a/dss.ggo b/dss.ggo
index 1662e0d..c594f6e 100644
--- a/dss.ggo
+++ b/dss.ggo
@@ -145,6 +145,16 @@ details="
 	received. See also the --exit-hook option.
 "
 
+groupoption "kill" K
+#~~~~~~~~~~~~~~~~~~~
+"Kill a running dss process"
+group="command"
+details="
+	This sends SIGTERM to the dss process that corresponds to the
+	given config file. If --dry-run is given, the PID of the dss
+	process is written to stdout, but no signal is sent.
+"
+
 ###############################
 section "Rsync-related options"
 ###############################
diff --git a/error.h b/error.h
index 9e910e2..3fd7531 100644
--- a/error.h
+++ b/error.h
@@ -68,6 +68,7 @@ static inline char *dss_strerror(int num)
 	DSS_ERROR(SIGNAL_SIG_ERR, "signal() returned SIG_ERR") \
 	DSS_ERROR(SIGNAL, "caught terminating signal") \
 	DSS_ERROR(BUG, "values of beta might cause dom!") \
+	DSS_ERROR(NOT_RUNNING, "dss not running") \
 
 
 /**
diff --git a/ipc.c b/ipc.c
index 8d969c7..053e0fd 100644
--- a/ipc.c
+++ b/ipc.c
@@ -313,6 +313,29 @@ static int mutex_lock(int id)
 	return 1;
 }
 
+static int mutex_try_lock(int id)
+{
+	int ret;
+
+	DSS_DEBUG_LOG("trying to lock\n");
+	struct sembuf sops[2] = {
+		{
+			.sem_num = 0,
+			.sem_op = 0,
+			.sem_flg = SEM_UNDO | IPC_NOWAIT
+		},
+		{
+			.sem_num = 0,
+			.sem_op = 1,
+			.sem_flg = SEM_UNDO | IPC_NOWAIT
+		}
+	};
+	ret = do_semop(id, sops, 2);
+	if (ret < 0)
+		return -ERRNO_TO_DSS_ERROR(errno);
+	return 1;
+}
+
 int lock_dss(char *config_file)
 {
 	int ret, key = get_key_or_die(config_file);
@@ -322,3 +345,21 @@ int lock_dss(char *config_file)
 		return ret;
 	return mutex_lock(ret);
 }
+
+int get_dss_pid(char *config_file, pid_t *pid)
+{
+	int ret, semid, key = get_key_or_die(config_file);
+
+	ret = mutex_get(key, 0);
+	if (ret < 0)
+		return ret;
+	semid = ret;
+	ret = semctl(semid, 1, GETPID);
+	if (ret < 0)
+		return -E_NOT_RUNNING;
+	*pid = ret;
+	ret = mutex_try_lock(semid);
+	if (ret >= 0)
+		return -E_NOT_RUNNING;
+	return 1;
+}
diff --git a/ipc.h b/ipc.h
index 4d64442..8646a8e 100644
--- a/ipc.h
+++ b/ipc.h
@@ -1 +1,2 @@
 int lock_dss(char *config_file);
+int get_dss_pid(char *config_file, pid_t *pid);