src/bindings: add features bitmask to struct pidns_store

This bitmask can be used to represent a per-instance (technically,
per pid namespace) features configuration (toggle-like).

Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>

Author: mihalicyn

src/bindings.c

@@ -362,7 +362,7 @@ static void save_initpid(ino_t pidns_inode, pid_t pid)
 
 	ino_hash = HASH(pidns_inode);
 	*entry = (struct pidns_store){
-		.version	= 1,
+		.version	= 2,
 		.ino		= pidns_inode,
 		.initpid	= pid,
 		.ctime		= st.st_ctime,
@@ -643,6 +643,55 @@ pid_t lookup_initpid_in_store(pid_t pid)
 	return hashed_pid;
 }
 
+bool check_set_lxcfs_feature(pid_t pid, enum lxcfs_feature_op op, __u64 feature)
+{
+	bool ret = false;
+	struct pidns_store *entry;
+	ino_t pidns_ino;
+
+	pidns_ino = get_pidns_ino(pid);
+	if (!pidns_ino)
+		return ret;
+
+	store_lock();
+
+	entry = lookup_verify_pidns_entry(pidns_ino);
+	if (!entry)
+		goto out;
+
+	if (entry->version < 2)
+		goto out;
+
+	switch (op) {
+	case LXCFS_FEATURE_CHECK:
+		ret = entry->features & feature;
+
+		break;
+	case LXCFS_FEATURE_SET:
+		entry->features |= feature;
+
+		/*
+		 * As we have enabled feature, this entry
+		 * must be kept across lxcfs live reloads.
+		 */
+		entry->keep_on_reload = true;
+
+		ret = true;
+
+		break;
+	case LXCFS_FEATURE_CLEAR:
+		entry->features &= ~feature;
+		ret = true;
+
+		break;
+	}
+
+out:
+	store_unlock();
+
+	return ret;
+}
+
 /*
  * Functions needed to setup cgroups in the __constructor__.
  */

src/bindings.h

@@ -108,6 +108,12 @@ struct file_info {
 	int cached;
 };
 
+enum lxcfs_feature_op {
+	LXCFS_FEATURE_CHECK,
+	LXCFS_FEATURE_SET,
+	LXCFS_FEATURE_CLEAR,
+};
+
 /*
  * A table caching which pid is init for a pid namespace.
  * When looking up which pid is init for $qpid, we first
@@ -139,6 +145,9 @@ struct pidns_store {
 
 	/* Do not free on liblxcfs reload (contains useful persistent data) */
 	bool keep_on_reload;
+
+	/* bit mask for per-instance configuration options (on/off) */
+	__u64 features;
 };
 
 /* lol - look at how they are allocated in the kernel */
@@ -176,6 +185,7 @@ typedef int (*pidns_store_iter_func_t) (struct pidns_store *cur, void *data);
 
 extern int iter_initpid_store(pidns_store_iter_func_t f, void *data);
 extern pid_t lookup_initpid_in_store(pid_t qpid);
+extern bool check_set_lxcfs_feature(pid_t pid, enum lxcfs_feature_op op, __u64 feature);
 extern void prune_init_slice(char *cg);
 extern bool supports_pidfd(void);
 extern bool liblxcfs_functional(void);