[lxc-devel] [PATCH 3/9] Enable get_cgroup_mount to search for mount points satisfying multiple subsystems at once

[Christian Seiler]

lxc-attach functionality reads /proc/init_pid/cgroup to determine the cgroup
of the container for a given subsystem. However, since subsystems may be
mounted together, we want to be on the safe side and be sure that we really
find the correct mount point, so we allow get_cgroup_mount to check for
*all* the subsystems; the subsystem parameter may now be a comma-separated
list.
---
 src/lxc/cgroup.c |   31 ++++++++++++++++++++++++++++++-
 1 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/src/lxc/cgroup.c b/src/lxc/cgroup.c
index 6ae67bd..2e04c79 100644
--- a/src/lxc/cgroup.c
+++ b/src/lxc/cgroup.c
@@ -52,6 +52,35 @@ enum {
 	CGROUP_CLONE_CHILDREN,
 };
 
+static char *hasmntopt_multiple(struct mntent *mntent, const char *options)
+{
+	const char *ptr = options;
+	const char *ptr2 = strchr(options, ',');
+	char *result;
+
+	while (ptr2 != NULL) {
+		char *option = strndup(ptr, ptr2 - ptr);
+		if (!option) {
+			SYSERROR("Temporary memory allocation error");
+			return NULL;
+		}
+
+		result = hasmntopt(mntent, option);
+		free(option);
+
+		if (!result) {
+			return NULL;
+		}
+
+		ptr = ptr2 + 1;
+		ptr2 = strchr(ptr, ',');
+	}
+
+	/* for multiple mount options, the return value is basically NULL
+	 * or non-NULL, so this should suffice for our purposes */
+	return hasmntopt(mntent, ptr);
+}
+
 static int get_cgroup_mount(const char *subsystem, char *mnt)
 {
 	struct mntent *mntent;
@@ -67,7 +96,7 @@ static int get_cgroup_mount(const char *subsystem, char *mnt)
 
 		if (strcmp(mntent->mnt_type, "cgroup"))
 			continue;
-		if (!subsystem || hasmntopt(mntent, subsystem)) {
+		if (!subsystem || hasmntopt_multiple(mntent, subsystem)) {
 			strcpy(mnt, mntent->mnt_dir);
 			fclose(file);
 			DEBUG("using cgroup mounted at '%s'", mnt);
-- 
1.7.2.5