[CRIU] [PATCH v3 36/55] restore: Implement set_next_pid() helper

[Andrei Vagin]

On Mon, Apr 10, 2017 at 11:21:00AM +0300, Kirill Tkhai wrote:
> Move next pid writing functionality to separate function.
> Also make set_next_pid() skip INIT_PID, as I'm going to
> call this function unconditionally in next patches.
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/cr-restore.c     |   40 ++++++++++++++++++++++++++++++++++------
>  criu/include/pstree.h |    1 +
>  2 files changed, 35 insertions(+), 6 deletions(-)
> 
> diff --git a/criu/cr-restore.c b/criu/cr-restore.c
> index a99a9be3c..be119274c 100644
> --- a/criu/cr-restore.c
> +++ b/criu/cr-restore.c
> @@ -282,6 +282,34 @@ static int root_prepare_shared(void)
>  	return ret;
>  }
>  
> +int __set_next_pid(pid_t pid)
> +{
> +	char buf[32];
> +	int len, fd;
> +
> +	fd = open_proc_rw(PROC_GEN, LAST_PID_PATH);
> +	if (fd < 0)
> +		return -1;
> +
> +	len = snprintf(buf, sizeof(buf), "%d", pid - 1);
> +	len -= write(fd, buf, len);
> +	close(fd);

close() can over-write errno
> +
> +	if (len) {
> +		pr_perror("%d: Write %s to %s", pid, buf, LAST_PID_PATH);
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
> +static int set_next_pid(struct ns_id *ns, struct pid *pid)
> +{
> +	if (pid->ns[0].virt == INIT_PID)
> +		return 0;
> +	return __set_next_pid(pid->ns[0].virt);
> +}
> +
>  static rt_sigaction_t sigchld_act;
>  /*
>   * If parent's sigaction has blocked SIGKILL (which is non-sence),
> @@ -977,12 +1005,16 @@ static inline int fork_with_pid(struct pstree_item *item)
>  	struct cr_clone_arg ca;
>  	int ret = -1;
>  	pid_t pid = vpid(item);
> +	struct ns_id *pid_ns;
>  
>  	if (item != root_item)
>  		item->user_ns = current->user_ns;
>  	else
>  		item->user_ns = root_user_ns;
>  
> +	pid_ns = lookup_ns_by_id(item->ids->pid_ns_id, &pid_ns_desc);
> +	BUG_ON(!pid_ns);
> +
>  	if (item->pid->state != TASK_HELPER) {
>  		if (open_core(pid, &ca.core))
>  			return -1;
> @@ -1021,9 +1053,6 @@ static inline int fork_with_pid(struct pstree_item *item)
>  	pr_info("Forking task with %d pid (flags 0x%lx)\n", pid, ca.clone_flags);
>  
>  	if (!(ca.clone_flags & CLONE_NEWPID)) {
> -		char buf[32];
> -		int len;
> -
>  		ca.fd = open_proc_rw(PROC_GEN, LAST_PID_PATH);
>  		if (ca.fd < 0)
>  			goto err;
> @@ -1034,9 +1063,8 @@ static inline int fork_with_pid(struct pstree_item *item)
>  			goto err;
>  		}
>  
> -		len = snprintf(buf, sizeof(buf), "%d", pid - 1);
> -		if (write(ca.fd, buf, len) != len) {
> -			pr_perror("%d: Write %s to %s", pid, buf, LAST_PID_PATH);
> +		if (set_next_pid(pid_ns, item->pid) < 0) {
> +			pr_err("Can't set next pid\n");
>  			goto err_unlock;
>  		}
>  	} else {
> diff --git a/criu/include/pstree.h b/criu/include/pstree.h
> index b8b8dd3f5..05e5b1e8f 100644
> --- a/criu/include/pstree.h
> +++ b/criu/include/pstree.h
> @@ -137,4 +137,5 @@ extern void pstree_free_cores(struct pstree_item *item);
>  extern int collect_pstree_ids(void);
>  
>  extern int preorder_pstree_traversal(struct pstree_item *item, int (*f)(struct pstree_item *));
> +extern int __set_next_pid(pid_t pid);
>  #endif /* __CR_PSTREE_H__ */
>