introduce semaphore for concurrent connecting ssh

instead of ssh_estab_queue (delay-based approach). MaxStartups in
sshd_config limits number of conccurent incoming ssh connections.
mscp_opts->max_startups adjusts this value.

include/mscp.h

@@ -43,6 +43,7 @@ struct mscp_opts {
 	size_t	max_chunk_sz;	/** maximum chunk size (default file size/nr_threads) */
 	size_t	buf_sz;		/** buffer size, default 16k. */
 	char	coremask[MSCP_MAX_COREMASK_STR]; /** hex to specifiy usable cpu cores */
+	int	max_startups;	/* sshd MaxStartups conccurent connections */
 
 	int	severity; 	/** messaging severity. set MSCP_SERVERITY_* */
 	int	msg_fd;		/** fd to output message. default STDOUT (0),

src/mscp.c

@@ -2,6 +2,7 @@
 #include <unistd.h>
 #include <math.h>
 #include <pthread.h>
+#include <semaphore.h>
 #include <sys/time.h>
 
 #include <list.h>       
@@ -13,55 +14,6 @@
 #include <message.h>
 #include <mscp.h>
 
-struct ssh_estab_queue {
-	lock		lock;
-	struct timeval	enter;
-	long		delay;	/* msec */
-};
-
-static long timeval_sub(struct timeval a, struct timeval b)
-{
-	unsigned long sec, usec;
-	if (a.tv_usec < b.tv_usec) {
-		a.tv_usec += 1000000;
-		a.tv_sec--;
-	}
-
-	sec = a.tv_sec - b.tv_sec;
-	usec = a.tv_usec - b.tv_usec;
-	return sec * 1000000 + usec;
-}
-
-static void ssh_estab_queue_init(struct ssh_estab_queue *q)
-{
-	memset(q, 0, sizeof(q));
-	lock_init(&q->lock);
-	q->delay = 100000; /* To be configurable */
-}
-
-static void ssh_estab_queue_ready(struct ssh_estab_queue *q)
-{
-	struct timeval now;
-	long delta;
-
-	LOCK_ACQUIRE_THREAD(&q->lock);
-	if (q->enter.tv_sec == 0 && q->enter.tv_usec == 0) {
-		/* I'm the first one. */
-		goto ready;
-	}
-
-	gettimeofday(&now, NULL);
-	delta = timeval_sub(now, q->enter);
-	if (delta <= q->delay) {
-		/* wait until enter + delay time */
-		usleep(q->delay - delta);
-	}
-ready:
-	gettimeofday(&q->enter, NULL);
-	LOCK_RELEASE_THREAD();
-}
-
-
 
 struct mscp {
 	char			*remote;	/* remote host (and uername) */
@@ -74,7 +26,8 @@ struct mscp {
 	int			*cores;		/* usable cpu cores by COREMASK */
 	int			nr_cores;	/* length of array of cores */
 
-	struct ssh_estab_queue	ssh_queue;
+	sem_t			sem;		/* semaphore for conccurent 
+						 * connecting ssh sessions */
 
 	sftp_session		first;		/* first sftp session */
 
@@ -117,6 +70,8 @@ struct src {
  * sftp_async_read returns 0.
  */
 
+#define DEFAULT_MAX_STARTUPS	8
+
 #define non_null_string(s) (s[0] != '\0')
 
 
@@ -236,6 +191,9 @@ static int validate_and_set_defaut_params(struct mscp_opts *o)
 		return -1;
 	}
 
+	if (o->max_startups == 0)
+		o->max_startups = DEFAULT_MAX_STARTUPS;
+
 	return 0;
 }
 
@@ -271,7 +229,10 @@ struct mscp *mscp_init(const char *remote_host, int direction,
 	INIT_LIST_HEAD(&m->src_list);
 	INIT_LIST_HEAD(&m->path_list);
 	chunk_pool_init(&m->cp);
-	ssh_estab_queue_init(&m->ssh_queue);
+	if (sem_init(&m->sem, 0, o->max_startups) < 0) {
+		mscp_set_error("failed to initialize semaphore: %s", strerrno());
+		goto free_out;
+	}
 
 	m->remote = strdup(remote_host);
 	if (!m->remote) {
@@ -591,14 +552,25 @@ void *mscp_copy_thread(void *arg)
 		}
         }
 
-	ssh_estab_queue_ready(&m->ssh_queue);
+	if (sem_wait(&m->sem) < 0) {
+		mscp_set_error("sem_wait: %s\n", strerrno());
+		mpr_err(m->msg_fp, "%s", mscp_get_error());
+		goto err_out;
+	}
+
 	mpr_notice(m->msg_fp, "connecting to %s for a copy thread[%d]...\n",
 		   m->remote, t->id);
 	t->sftp = ssh_init_sftp_session(m->remote, m->ssh_opts);
+
+	if (sem_post(&m->sem) < 0) {
+		mscp_set_error("sem_post: %s\n", strerrno());
+		mpr_err(m->msg_fp, "%s", mscp_get_error());
+		goto err_out;
+	}
+
 	if (!t->sftp) {
 		mpr_err(m->msg_fp, "copy thread[%d]: %s\n", t->id, mscp_get_error());
-		t->ret = -1;
-		return NULL;
+		goto err_out;
 	}
 
         switch (m->direction) {
@@ -641,6 +613,10 @@ void *mscp_copy_thread(void *arg)
 			       c->p->path, c->off, c->off + c->len);
 
         return NULL;
+
+err_out:
+	t->ret = -1;
+	return NULL;
 }