s3-prefork: implement prefork framework

Primarily built for forked off rpc service daemons, but not tied to rpc
services and generic enough to be used elsewhere easily.

Signed-off-by: Andreas Schneider <asn@samba.org>

1 files changed, 502 insertions, 0 deletions

diff --git a/source3/lib/server_prefork.c b/source3/lib/server_prefork.c
new file mode 100644
index 0000000000..4aa3f482cc
--- /dev/null
+++ b/source3/lib/server_prefork.c
@@ -0,0 +1,502 @@
+/*
+   Unix SMB/CIFS implementation.
+   Common server globals
+
+   Copyright (C) Simo Sorce <idra@samba.org> 2011
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "includes.h"
+#include "system/time.h"
+#include "system/shmem.h"
+#include "system/filesys.h"
+#include "server_prefork.h"
+#include "../lib/util/util.h"
+
+struct prefork_pool {
+
+	int listen_fd;
+	int lock_fd;
+
+	prefork_main_fn_t *main_fn;
+	void *private_data;
+
+	int pool_size;
+	struct pf_worker_data *pool;
+};
+
+int prefork_pool_destructor(struct prefork_pool *pfp)
+{
+	munmap(pfp->pool, pfp->pool_size * sizeof(struct pf_worker_data));
+	return 0;
+}
+
+bool prefork_create_pool(struct tevent_context *ev_ctx,
+			 TALLOC_CTX *mem_ctx, int listen_fd,
+			 int min_children, int max_children,
+			 prefork_main_fn_t *main_fn, void *private_data,
+			 struct prefork_pool **pf_pool)
+{
+	struct prefork_pool *pfp;
+	pid_t pid;
+	time_t now = time(NULL);
+	size_t data_size;
+	int ret;
+	int i;
+
+	pfp = talloc(mem_ctx, struct prefork_pool);
+	if (!pfp) {
+		DEBUG(1, ("Out of memory!\n"));
+		return false;
+	}
+	pfp->listen_fd = listen_fd;
+	pfp->main_fn = main_fn;
+	pfp->private_data = private_data;
+
+	pfp->lock_fd = create_unlink_tmp(NULL);
+	if (pfp->lock_fd == -1) {
+		DEBUG(1, ("Failed to create prefork lock fd!\n"));
+		talloc_free(pfp);
+		return false;
+	}
+
+	pfp->pool_size = max_children;
+	data_size = sizeof(struct pf_worker_data) * max_children;
+
+	pfp->pool = mmap(NULL, data_size, PROT_READ|PROT_WRITE,
+			 MAP_SHARED|MAP_ANONYMOUS, -1, 0);
+	if (pfp->pool == MAP_FAILED) {
+		DEBUG(1, ("Failed to mmap memory for prefork pool!\n"));
+		talloc_free(pfp);
+		return false;
+	}
+	talloc_set_destructor(pfp, prefork_pool_destructor);
+
+	for (i = 0; i < min_children; i++) {
+		pid = sys_fork();
+		switch (pid) {
+		case -1:
+			DEBUG(1, ("Failed to prefork child n. %d !\n", i));
+			break;
+
+		case 0: /* THE CHILD */
+
+			pfp->pool[i].status = PF_WORKER_IDLE;
+
+			ret = pfp->main_fn(ev_ctx, &pfp->pool[i],
+					   pfp->listen_fd, pfp->lock_fd,
+					   pfp->private_data);
+			exit(ret);
+
+		default: /* THE PARENT */
+			pfp->pool[i].pid = pid;
+			pfp->pool[i].started = now;
+			break;
+		}
+	}
+
+	*pf_pool = pfp;
+	return true;
+}
+
+int prefork_add_children(struct tevent_context *ev_ctx,
+			 struct prefork_pool *pfp,
+			 int num_children)
+{
+	pid_t pid;
+	time_t now = time(NULL);
+	int ret;
+	int i, j;
+
+	for (i = 0, j = 0; i < pfp->pool_size && j < num_children; i++) {
+
+		if (pfp->pool[i].status != PF_WORKER_NONE) {
+			continue;
+		}
+
+		pid = sys_fork();
+		switch (pid) {
+		case -1:
+			DEBUG(1, ("Failed to prefork child n. %d !\n", j));
+			break;
+
+		case 0: /* THE CHILD */
+
+			pfp->pool[i].status = PF_WORKER_IDLE;
+			ret = pfp->main_fn(ev_ctx, &pfp->pool[i],
+					   pfp->listen_fd, pfp->lock_fd,
+					   pfp->private_data);
+
+			pfp->pool[i].status = PF_WORKER_EXITING;
+			exit(ret);
+
+		default: /* THE PARENT */
+			pfp->pool[i].pid = pid;
+			pfp->pool[i].started = now;
+			j++;
+			break;
+		}
+	}
+
+	DEBUG(5, ("Added %d children!\n", j));
+
+	return j;
+}
+
+struct prefork_oldest {
+	int num;
+	time_t started;
+};
+
+/* sort in inverse order */
+static int prefork_sort_oldest(const void *ap, const void *bp)
+{
+	struct prefork_oldest *a = (struct prefork_oldest *)ap;
+	struct prefork_oldest *b = (struct prefork_oldest *)bp;
+
+	if (a->started == b->started) {
+		return 0;
+	}
+	if (a->started < b->started) {
+		return 1;
+	}
+	return -1;
+}
+
+int prefork_retire_children(struct prefork_pool *pfp,
+			    int num_children, time_t age_limit)
+{
+	time_t now = time(NULL);
+	struct prefork_oldest *oldest;
+	int i, j;
+
+	oldest = talloc_array(pfp, struct prefork_oldest, pfp->pool_size);
+	if (!oldest) {
+		return -1;
+	}
+
+	for (i = 0; i < pfp->pool_size; i++) {
+		oldest[i].num = i;
+		if (pfp->pool[i].status == PF_WORKER_IDLE) {
+			oldest[i].started = pfp->pool[i].started;
+		} else {
+			oldest[i].started = now;
+		}
+	}
+
+	qsort(oldest, pfp->pool_size,
+		sizeof(struct prefork_oldest),
+		prefork_sort_oldest);
+
+	for (i = 0, j = 0; i < pfp->pool_size && j < num_children; i++) {
+		if (pfp->pool[i].status == PF_WORKER_IDLE &&
+		    pfp->pool[i].started <= age_limit) {
+			/* tell the child it's time to give up */
+			DEBUG(5, ("Retiring pid %d!\n", pfp->pool[i].pid));
+			pfp->pool[i].cmds = PF_SRV_MSG_EXIT;
+			kill(pfp->pool[i].pid, SIGHUP);
+			j++;
+		}
+	}
+
+	return j;
+}
+
+int prefork_count_active_children(struct prefork_pool *pfp, int *total)
+{
+	int i, a, t;
+
+	a = 0;
+	t = 0;
+	for (i = 0; i < pfp->pool_size; i++) {
+		if (pfp->pool[i].status == PF_WORKER_NONE) {
+			continue;
+		}
+
+		t++;
+
+		if (pfp->pool[i].num_clients == 0) {
+			continue;
+		}
+
+		a++;
+	}
+
+	*total = t;
+	return a;
+}
+
+/* to be used to finally mark a children as dead, so that it's slot can
+ * be reused */
+bool prefork_mark_pid_dead(struct prefork_pool *pfp, pid_t pid)
+{
+	int i;
+
+	for (i = 0; i < pfp->pool_size; i++) {
+		if (pfp->pool[i].pid == pid) {
+			if (pfp->pool[i].status != PF_WORKER_EXITING) {
+				DEBUG(2, ("pid %d terminated abnormally!\n",
+					  (int)pid));
+			}
+
+			/* reset all fields,
+			 * this makes status = PF_WORK_NONE */
+			memset(&pfp->pool[i], 0,
+				sizeof(struct pf_worker_data));
+
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/* ==== Functions used by children ==== */
+
+static SIG_ATOMIC_T pf_alarm;
+
+static void pf_alarm_cb(int signum)
+{
+	pf_alarm = 1;
+}
+
+
+/*
+ * Parameters:
+ * pf - the worker shared data structure
+ * lock_fd - the file descriptor used for locking
+ * timeout - expressed in seconds:
+ *		-1 never timeouts,
+ *		0 timeouts immediately
+ *		N seconds before timing out
+ *
+ * Returns values:
+ * negative errno on fatal error
+ * 0 on success to acquire lock
+ * -1 on timeout/lock held by other
+ * -2 on server msg to terminate
+ * ERRNO on other errors
+ */
+
+static int prefork_grab_lock(struct pf_worker_data *pf,
+			     int lock_fd, int timeout)
+{
+	struct flock lock;
+	int op;
+	int ret;
+
+	if (pf->cmds == PF_SRV_MSG_EXIT) {
+		return -2;
+	}
+
+	pf_alarm = 0;
+
+	if (timeout > 0) {
+		CatchSignal(SIGALRM, pf_alarm_cb);
+		alarm(timeout);
+	}
+
+	if (timeout == 0) {
+		op = F_SETLK;
+	} else {
+		op = F_SETLKW;
+	}
+
+	ret = 0;
+	do {
+		ZERO_STRUCT(lock);
+		lock.l_type = F_WRLCK;
+		lock.l_whence = SEEK_SET;
+
+		ret = fcntl(lock_fd, op, &lock);
+		if (ret == 0) break;
+
+		ret = errno;
+
+		if (pf->cmds == PF_SRV_MSG_EXIT) {
+			ret = -2;
+			goto done;
+		}
+
+		switch (ret) {
+		case EINTR:
+			break;
+
+		case EACCES:
+		case EAGAIN:
+			/* lock held by other proc */
+			ret = -1;
+			goto done;
+		default:
+			goto done;
+		}
+
+		if (pf_alarm == 1) {
+			/* timed out */
+			ret = -1;
+			goto done;
+		}
+	} while (timeout != 0);
+
+	if (ret != 0) {
+		/* We have the Lock */
+		pf->status = PF_WORKER_ACCEPTING;
+	}
+
+done:
+	if (timeout > 0) {
+		alarm(0);
+		CatchSignal(SIGALRM, SIG_IGN);
+	}
+
+	if (ret > 0) {
+		DEBUG(1, ("Failed to get lock (%d, %s)!\n",
+			  ret, strerror(ret)));
+	}
+	return ret;
+}
+
+/*
+ * Parameters:
+ * pf - the worker shared data structure
+ * lock_fd - the file descriptor used for locking
+ * timeout - expressed in seconds:
+ *		-1 never timeouts,
+ *		0 timeouts immediately
+ *		N seconds before timing out
+ *
+ * Returns values:
+ * negative errno on fatal error
+ * 0 on success to release lock
+ * -1 on timeout
+ * ERRNO on error
+ */
+
+static int prefork_release_lock(struct pf_worker_data *pf,
+				int lock_fd, int timeout)
+{
+	struct flock lock;
+	int op;
+	int ret;
+
+	pf_alarm = 0;
+
+	if (timeout > 0) {
+		CatchSignal(SIGALRM, pf_alarm_cb);
+		alarm(timeout);
+	}
+
+	if (timeout == 0) {
+		op = F_SETLK;
+	} else {
+		op = F_SETLKW;
+	}
+
+	do {
+		ZERO_STRUCT(lock);
+		lock.l_type = F_UNLCK;
+		lock.l_whence = SEEK_SET;
+
+		ret = fcntl(lock_fd, op, &lock);
+		if (ret == 0) break;
+
+		ret = errno;
+
+		if (ret != EINTR) {
+			goto done;
+		}
+
+		if (pf_alarm == 1) {
+			/* timed out */
+			ret = -1;
+			goto done;
+		}
+	} while (timeout != 0);
+
+done:
+	if (timeout > 0) {
+		alarm(0);
+		CatchSignal(SIGALRM, SIG_IGN);
+	}
+
+	if (ret > 0) {
+		DEBUG(1, ("Failed to release lock (%d, %s)!\n",
+			  ret, strerror(ret)));
+	}
+	return ret;
+}
+
+/* returns:
+ * negative errno on error
+ * -2 if server commands to terminate
+ * 0 if all ok
+ * ERRNO on other errors
+ */
+
+int prefork_wait_for_client(struct pf_worker_data *pf,
+			    int lock_fd, int listen_fd,
+			    struct sockaddr *addr,
+			    socklen_t *addrlen, int *fd)
+{
+	int ret;
+	int sd = -1;
+	int err;
+
+	ret = prefork_grab_lock(pf, lock_fd, -1);
+	if (ret != 0) {
+		return ret;
+	}
+
+	err = 0;
+	do {
+		sd = accept(listen_fd, addr, addrlen);
+
+		if (sd != -1) break;
+
+		if (errno == EINTR) {
+			if (pf->cmds == PF_SRV_MSG_EXIT) {
+				err = -2;
+			}
+		} else {
+			err = errno;
+		}
+
+	} while ((sd == -1) && (err == 0));
+
+	/* return lock now, even if the accept failed.
+	 * if it takes more than 10 seconds we are in deep trouble */
+	ret = prefork_release_lock(pf, lock_fd, 2);
+	if (ret != 0) {
+		/* we were unable to release the lock!! */
+		DEBUG(0, ("Terminating due to fatal failure!\n"));
+
+		/* Just exit we cannot hold the whole server, better to error
+		 * on this one client and hope it was a transiet problem */
+		err = -2;
+	}
+
+	if (err != 0) {
+		if (sd != -1) {
+			close(sd);
+			sd = -1;
+		}
+		return err;
+	}
+
+	pf->status = PF_WORKER_BUSY;
+	pf->num_clients++;
+	*fd = sd;
+	return 0;
+}