src/bindings: make struct pidns_store versionized

It's necessary as we want to be able to easily extend it
and use live reloads update mechanism.

This change does not break compatibility, because struct pidns_store
lifetime is limited to liblxcfs lifetime. But we'll make pidns_store
lifetime bigger that's why we need to start versionizing it.

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

Author: mihalicyn

src/bindings.c

@@ -320,6 +320,7 @@ static void save_initpid(ino_t pidns_inode, pid_t pid)
 
 	ino_hash = HASH(pidns_inode);
 	*entry = (struct pidns_store){
+		.version	= 0,
 		.ino		= pidns_inode,
 		.initpid	= pid,
 		.ctime		= st.st_ctime,

src/bindings.h

@@ -123,11 +123,18 @@ struct file_info {
  *	 cached initpid.
  */
 struct pidns_store {
+	/* increase version if the structure was changed */
+	__u16 version;
+
+	/* hash table key */
 	ino_t ino;     /* inode number for /proc/$pid/ns/pid */
-	pid_t initpid; /* the pid of nit in that ns */
+
+	/* next entry in hash table's bucket */
+	struct pidns_store *next;
+
+	pid_t initpid; /* the pid of init in that ns */
 	int init_pidfd;
 	int64_t ctime; /* the time at which /proc/$initpid was created */
-	struct pidns_store *next;
 	int64_t lastcheck;
 };