[CRIU] [PATCH v2 07/28] files: Allow to receive further fds

[Pavel Emelyanov]

On 11/30/2016 07:30 PM, Kirill Tkhai wrote:
> For moving to a single transport socket scheme, we should be able
> to receive a fd, which is not need at the moment, but it will
> be used in the future. So, we receive a further fd, and then
> continue to wait the fd, we really need now.
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/files.c         |   37 +++++++++++++++++++++++++++++++++++--
>  criu/include/files.h |    2 ++
>  2 files changed, 37 insertions(+), 2 deletions(-)
> 
> diff --git a/criu/files.c b/criu/files.c
> index de4ef17..806af26 100644
> --- a/criu/files.c
> +++ b/criu/files.c
> @@ -956,20 +956,51 @@ static int open_transport_fd(int pid, struct fdinfo_list_entry *fle)
>  	return -1;
>  }
>  
> +static bool insane_fle(struct fdinfo_list_entry *alien_fle)

So is it insane or alien? :)

> +{
> +	struct fdinfo_list_entry *fle;
> +
> +	list_for_each_entry(fle, &rsti(current)->used, used_list)
> +		if (alien_fle == fle)
> +			return false;
> +	pr_err("Insane fle=%p, pid=%d\n", alien_fle, current->pid.virt);
> +	return true;
> +}
> +
> +static int recv_further_fle(struct fdinfo_list_entry *fle, int fd)

This routine keeps alien (or insane?) fle in local task for future use. Let's
better call this one 'park_fd' or 'keep_fd_for_future'. Some name to reflect
the fact that fd is not received, but is kept until better times.

> +{
> +	BUG_ON(fle->received);
> +	fle->received = 1;
> +	if (close(fle->fe->fd) < 0) {
> +		pr_perror("Can't close transport fd\n");
> +		return -1;
> +	}
> +	return reopen_fd_as(fle->fe->fd, fd);
> +}
> +
>  int recv_fd_from_peer(struct fdinfo_list_entry *fle)
>  {
>  	struct fdinfo_list_entry *tmp;
>  	int fd, ret;
>  
> +	if (fle->received)
> +		return fle->fe->fd;
> +again:
>  	ret = recv_fds(fle->fe->fd, &fd, 1, (void *)&tmp, sizeof(struct fdinfo_list_entry *));
>  	if (ret)
>  		return -1;
>  
>  	if (tmp != fle) {
> -		pr_err("Received wrong fle\n");
> -		return -1;
> +		pr_info("Further fle=%p, pid=%d\n", tmp, fle->pid);
> +		if (insane_fle(fle))
> +			return -1;
> +		if (recv_further_fle(tmp, fd))
> +			return -1;
> +		goto again;
>  	}
>  	close(fle->fe->fd);
> +	BUG_ON(fle->received);

if (fle->received) is checked above, why do we need BUG_ON() here?

> +	fle->received = 1;
>  
>  	return fd;
>  }
> @@ -1013,6 +1044,8 @@ static int send_fd_to_self(int fd, struct fdinfo_list_entry *fle)
>  		return -1;
>  	}
>  
> +	fle->received = 1;
> +
>  	return 0;
>  }
>  
> diff --git a/criu/include/files.h b/criu/include/files.h
> index c9b59c3..bd20e59 100644
> --- a/criu/include/files.h
> +++ b/criu/include/files.h
> @@ -72,12 +72,14 @@ struct fdinfo_list_entry {
>  	int			pid;
>  	futex_t			real_pid;
>  	FdinfoEntry		*fe;
> +	u8			received:1;

bool?

>  };
>  
>  static inline void fle_init(struct fdinfo_list_entry *fle, int pid, FdinfoEntry *fe)
>  {
>  	fle->pid = pid;
>  	fle->fe = fe;
> +	fle->received = 0;
>  }
>  
>  /* reports whether fd_a takes prio over fd_b */
> 
> .
>