util: add ability to change a file descriptor on procfs (v2)

When a pidns is dumped, crtools uses procfs from this pidns
for getting information about zombies.

v2: Use close_proc() instead of restore_proc_fd().
    A current proc will be opened again, if it's required.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util.h

@@ -178,6 +178,7 @@ int set_proc_mountpoint(char *path);
 void close_proc(void);
 int open_pid_proc(pid_t pid);
 int close_pid_proc(void);
+int set_proc_fd(int fd);
 
 int do_open_proc(pid_t pid, int flags, const char *fmt, ...);
 

util.c

@@ -170,6 +170,21 @@ void close_proc()
 	proc_dir_fd = -1;
 }
 
+int set_proc_fd(int fd)
+{
+	int sfd = get_service_fd(PROC_FD_OFF);
+
+	sfd = dup2(fd, sfd);
+	if (sfd < 0) {
+		pr_perror("Can't set proc fd\n");
+		return -1;
+	}
+
+	proc_dir_fd = sfd;
+
+	return 0;
+}
+
 int set_proc_mountpoint(char *path)
 {
 	int sfd = get_service_fd(PROC_FD_OFF), fd;