[Lxc-users] [PATCH] lxclock and lxccontainer: switch from flock to fcntl

[Serge Hallyn]

flock is not supported on nfs.  fcntl is at least supported on newer
(v3 and above) nfs.

Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
 src/lxc/lxccontainer.c |   22 +++++++++++++++++-----
 src/lxc/lxclock.c      |   16 ++++++++++++++--
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
index 2edf749..cf5252b 100644
--- a/src/lxc/lxccontainer.c
+++ b/src/lxc/lxccontainer.c
@@ -23,6 +23,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <sched.h>
 #include "config.h"
 #include "lxc.h"
@@ -39,7 +40,6 @@
 #include <lxc/utils.h>
 #include <lxc/monitor.h>
 #include <sched.h>
-#include <fcntl.h>
 #include <arpa/inet.h>
 #include <ifaddrs.h>
 
@@ -66,6 +66,8 @@ int ongoing_create(struct lxc_container *c)
 	int len = strlen(c->config_path) + strlen(c->name) + 10;
 	char *path = alloca(len);
 	int fd, ret;
+	struct flock lk;
+
 	ret = snprintf(path, len, "%s/%s/partial", c->config_path, c->name);
 	if (ret < 0 || ret >= len) {
 		ERROR("Error writing partial pathname");
@@ -82,8 +84,12 @@ int ongoing_create(struct lxc_container *c)
 		process_unlock();
 		return 0;
 	}
-	if ((ret = flock(fd, LOCK_EX | LOCK_NB)) == -1 &&
-			errno == EWOULDBLOCK) {
+	lk.l_type = F_WRLCK;
+	lk.l_whence = SEEK_SET;
+	lk.l_start = 0;
+	lk.l_len = 0;
+	lk.l_pid = -1;
+	if (fcntl(fd, F_GETLK, &lk) == 0 && lk.l_pid != -1) {
 		// create is still ongoing
 		close(fd);
 		process_unlock();
@@ -101,6 +107,8 @@ int create_partial(struct lxc_container *c)
 	int len = strlen(c->config_path) + strlen(c->name) + 10;
 	char *path = alloca(len);
 	int fd, ret;
+	struct flock lk;
+
 	ret = snprintf(path, len, "%s/%s/partial", c->config_path, c->name);
 	if (ret < 0 || ret >= len) {
 		ERROR("Error writing partial pathname");
@@ -108,12 +116,16 @@ int create_partial(struct lxc_container *c)
 	}
 	if (process_lock())
 		return -1;
-	if ((fd=open(path, O_CREAT | O_EXCL, 0755)) < 0) {
+	if ((fd=open(path, O_RDWR | O_CREAT | O_EXCL, 0755)) < 0) {
 		SYSERROR("Erorr creating partial file");
 		process_unlock();
 		return -1;
 	}
-	if (flock(fd, LOCK_EX) < 0) {
+	lk.l_type = F_WRLCK;
+	lk.l_whence = SEEK_SET;
+	lk.l_start = 0;
+	lk.l_len = 0;
+	if (fcntl(fd, F_SETLKW, &lk) < 0) {
 		SYSERROR("Error locking partial file %s", path);
 		close(fd);
 		process_unlock();
diff --git a/src/lxc/lxclock.c b/src/lxc/lxclock.c
index 4bbe873..d004cc5 100644
--- a/src/lxc/lxclock.c
+++ b/src/lxc/lxclock.c
@@ -23,6 +23,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>
+#include <fcntl.h>
 #include <lxc/utils.h>
 #include <lxc/log.h>
 #include <lxc/lxccontainer.h>
@@ -111,6 +112,7 @@ out:
 int lxclock(struct lxc_lock *l, int timeout)
 {
 	int ret = -1, saved_errno = errno;
+	struct flock lk;
 
 	switch(l->type) {
 	case LXC_LOCK_ANON_SEM:
@@ -152,7 +154,11 @@ int lxclock(struct lxc_lock *l, int timeout)
 				goto out;
 			}
 		}
-		ret = flock(l->u.f.fd, LOCK_EX);
+		lk.l_type = F_WRLCK;
+		lk.l_whence = SEEK_SET;
+		lk.l_start = 0;
+		lk.l_len = 0;
+		ret = fcntl(l->u.f.fd, F_SETLKW, &lk);
 		process_unlock();
 		if (ret == -1)
 			saved_errno = errno;
@@ -167,6 +173,7 @@ out:
 int lxcunlock(struct lxc_lock *l)
 {
 	int ret = 0, saved_errno = errno;
+	struct flock lk;
 
 	switch(l->type) {
 	case LXC_LOCK_ANON_SEM:
@@ -179,7 +186,12 @@ int lxcunlock(struct lxc_lock *l)
 	case LXC_LOCK_FLOCK:
 		process_lock();
 		if (l->u.f.fd != -1) {
-			if ((ret = flock(l->u.f.fd, LOCK_UN)) < 0)
+			lk.l_type = F_UNLCK;
+			lk.l_whence = SEEK_SET;
+			lk.l_start = 0;
+			lk.l_len = 0;
+			ret = fcntl(l->u.f.fd, F_SETLK, &lk);
+			if (ret < 0)
 				saved_errno = errno;
 			close(l->u.f.fd);
 			l->u.f.fd = -1;
-- 
1.7.9.5