[lxc-devel] [PATCH 1/2]: Ensure freezer state has changed

[Sukadev Bhattiprolu]

From: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
Subject: [PATCH 1/2] Ensure frezer state has changed

A write to the freezer.state file does not gurantee that the state has
changed. To ensure that the freezer state is either FROZEN or THAWED,
read the freezer state and if it has not changed, repeat the write.

Changelog[v2]:
	- Minor reorg of code
	- Comments from Daniel Lezcano:
		- lseek() before each read/write of freezer.state
		- Have lxc_freeze_unfreeze() return -1 on error

Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
---
 src/lxc/freezer.c |   50 +++++++++++++++++++++++++++++++++++++++++++-------
 1 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/src/lxc/freezer.c b/src/lxc/freezer.c
index cff954e..d144f89 100644
--- a/src/lxc/freezer.c
+++ b/src/lxc/freezer.c
@@ -42,6 +42,7 @@ static int freeze_unfreeze(const char *name, int freeze)
 {
 	char *nsgroup;
 	char freezer[MAXPATHLEN], *f;
+	char tmpf[32];
 	int fd, ret;
 	
 	ret = lxc_cgroup_path_get(&nsgroup, name);
@@ -50,7 +51,7 @@ static int freeze_unfreeze(const char *name, int freeze)
 
 	snprintf(freezer, MAXPATHLEN, "%s/freezer.state", nsgroup);
 
-	fd = open(freezer, O_WRONLY);
+	fd = open(freezer, O_RDWR);
 	if (fd < 0) {
 		SYSERROR("failed to open freezer for '%s'", name);
 		return -1;
@@ -58,22 +59,57 @@ static int freeze_unfreeze(const char *name, int freeze)
 
 	if (freeze) {
 		f = "FROZEN";
-		ret = write(fd, f, strlen(f) + 1) < 0;
+		ret = write(fd, f, strlen(f) + 1);
 	} else {
 		f = "THAWED";
-		ret = write(fd, f, strlen(f) + 1) < 0;
+		ret = write(fd, f, strlen(f) + 1);
 
 		/* compatibility code with old freezer interface */
-		if (ret) {
+		if (ret < 0) {
 			f = "RUNNING";
 			ret = write(fd, f, strlen(f) + 1) < 0;
 		}
 	}
 
-	close(fd);
-	if (ret) 
-		SYSERROR("failed to write to '%s'", freezer);
+	if (ret < 0) {
+		SYSERROR("failed to write '%s' to '%s'", f, freezer);
+		goto out;
+	}
+
+	while (1) {
+		ret = lseek(fd, 0L, SEEK_SET);
+		if (ret < 0) {
+			SYSERROR("failed to lseek on file '%s'", freezer);
+			goto out;
+		}
+
+		ret = read(fd, tmpf, sizeof(tmpf));
+		if (ret < 0) {
+			SYSERROR("failed to read to '%s'", freezer);
+			goto out;
+		}
+
+		ret = strncmp(f, tmpf, strlen(f));
+		if (!ret)
+			break;		/* Success */
 
+		sleep(1);
+
+		ret = lseek(fd, 0L, SEEK_SET);
+		if (ret < 0) {
+			SYSERROR("failed to lseek on file '%s'", freezer);
+			goto out;
+		}
+
+		ret = write(fd, f, strlen(f) + 1); 
+		if (ret < 0) {
+			SYSERROR("failed to write '%s' to '%s'", f, freezer);
+			goto out;
+		}
+	}
+
+out:
+	close(fd);
 	return ret;
 }
 
-- 
1.6.0.4