[lxc-devel] [PATCH 2/4] Add lxc_cgroup_attach function

[Christian Seiler]

This commit adds the lxc_cgroup_attach function that adds a pid to the tasks
file of a specific cgroup in all subsystems. This is required for lxc-attach
to be able to put newly started processes in the same cgroup as the
container.
---
 src/lxc/cgroup.c |   47 +++++++++++++++++++++++++++++++++++++++++++++++
 src/lxc/cgroup.h |    1 +
 2 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/src/lxc/cgroup.c b/src/lxc/cgroup.c
index 6ae67bd..db5d2fa 100644
--- a/src/lxc/cgroup.c
+++ b/src/lxc/cgroup.c
@@ -433,3 +433,50 @@ int lxc_cgroup_nrtasks(const char *name)
 
 	return count;
 }
+
+int lxc_cgroup_attach(const char *name, pid_t pid)
+{
+	char cgname[MAXPATHLEN];
+	struct mntent *mntent;
+	FILE *file = NULL;
+	int err = -1;
+	int found = 0;
+
+	file = setmntent(MTAB, "r");
+	if (!file) {
+		SYSERROR("failed to open %s", MTAB);
+		return -1;
+	}
+
+	while ((mntent = getmntent(file))) {
+
+		DEBUG("checking '%s' (%s)", mntent->mnt_dir, mntent->mnt_type);
+
+		if (!strcmp(mntent->mnt_type, "cgroup")) {
+
+			INFO("[%d] found cgroup mounted at '%s',opts='%s'",
+			     ++found, mntent->mnt_dir, mntent->mnt_opts);
+
+			snprintf(cgname, MAXPATHLEN, "%s/%s",
+			         mntent->mnt_dir, name);
+
+			if (access(cgname, F_OK)) {
+				ERROR("No cgroup '%s' found "
+				      "in subsystem mounted at '%s'",
+				      name, mntent->mnt_dir);
+				goto out;
+			}
+
+			err = cgroup_attach(cgname, pid);
+			if (err)
+				goto out;
+		}
+	};
+
+	if (!found)
+		ERROR("No cgroup mounted on the system");
+
+out:
+	endmntent(file);
+	return err;
+}
diff --git a/src/lxc/cgroup.h b/src/lxc/cgroup.h
index 31dd2de..3c90696 100644
--- a/src/lxc/cgroup.h
+++ b/src/lxc/cgroup.h
@@ -30,5 +30,6 @@ extern int lxc_cgroup_create(const char *name, pid_t pid);
 extern int lxc_cgroup_destroy(const char *name);
 extern int lxc_cgroup_path_get(char **path, const char *subsystem, const char *name);
 extern int lxc_cgroup_nrtasks(const char *name);
+extern int lxc_cgroup_attach(const char *name, pid_t pid);
 extern int lxc_ns_is_mounted(void);
 #endif
-- 
1.7.2.5