From: Christian Brauner <christian.brauner@ubuntu.com>
Date: Tue, 2 Feb 2021 15:59:38 +0000 (+0100)
Subject: cgroups: add cgroup_get()
X-Git-Tag: lxc-5.0.0~305^2~31
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b1356424886989139f83a63f0709007e5792d1f5;p=thirdparty%2Flxc.git

cgroups: add cgroup_get()

This is a unified hierarchy only method which doesn't need to initialize a full
cgroup driver. Instead, it relies on the command socket to retrieve a cgroup2
file descriptor to the container's cgroup.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---

diff --git a/src/lxc/cgroups/cgfsng.c b/src/lxc/cgroups/cgfsng.c
index 6b89a4acc..b8c6e640e 100644
--- a/src/lxc/cgroups/cgfsng.c
+++ b/src/lxc/cgroups/cgfsng.c
@@ -2500,6 +2500,31 @@ __cgfsng_ops static bool cgfsng_attach(struct cgroup_ops *ops,
 	return true;
 }
 
+int cgroup_get(struct lxc_conf *conf, const char *filename,
+	       char *buf, size_t len,
+	       const char *name, const char *lxcpath)
+{
+	__do_close int unified_fd = -EBADF;
+	ssize_t ret;
+
+	if (!conf || is_empty_string(filename) || is_empty_string(name) ||
+	    is_empty_string(lxcpath))
+		return ret_errno(EINVAL);
+
+	if ((buf && !len) || (len && !buf))
+		return ret_errno(EINVAL);
+
+	unified_fd = lxc_cmd_get_cgroup2_fd(name, lxcpath);
+	if (unified_fd < 0)
+		return ret_errno(ENOCGROUP2);
+
+	ret = lxc_read_try_buf_at(unified_fd, filename, buf, len);
+	if (ret < 0)
+		SYSERROR("Failed to read cgroup value");
+
+	return ret;
+}
+
 /* Called externally (i.e. from 'lxc-cgroup') to query cgroup limits.  Here we
  * don't have a cgroup_data set up, so we ask the running container through the
  * commands API for the cgroup path.
diff --git a/src/lxc/cgroups/cgroup.h b/src/lxc/cgroups/cgroup.h
index 7d95dfd35..b47561daa 100644
--- a/src/lxc/cgroups/cgroup.h
+++ b/src/lxc/cgroups/cgroup.h
@@ -191,6 +191,9 @@ __hidden extern void prune_init_scope(char *cg);
 
 __hidden extern int cgroup_attach(const struct lxc_conf *conf, const char *name,
 				  const char *lxcpath, pid_t pid);
+__hidden extern int cgroup_get(struct lxc_conf *conf, const char *filename,
+                               char *buf, size_t len, const char *name,
+                               const char *lxcpath);
 
 static inline bool pure_unified_layout(const struct cgroup_ops *ops)
 {