[CRIU] [PATCH RFC 05/30] files: Send/receive fds with pointers on their struct fdinfo_list_entry in receiver

[Kirill Tkhai]

On 02.11.2016 08:18, Andrei Vagin wrote:
> On Tue, Nov 01, 2016 at 05:31:09PM +0300, Kirill Tkhai wrote:
>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>> ---
>>  criu/files.c         |   21 +++++++++++++++++++--
>>  criu/include/files.h |    1 +
>>  criu/pipes.c         |    2 +-
>>  criu/sk-unix.c       |    2 +-
>>  criu/tty.c           |    2 +-
>>  5 files changed, 23 insertions(+), 5 deletions(-)
>>
>> diff --git a/criu/files.c b/criu/files.c
>> index 97b4e95..348f2c7 100644
>> --- a/criu/files.c
>> +++ b/criu/files.c
>> @@ -957,6 +957,23 @@ static int open_transport_fd(int pid, struct fdinfo_list_entry *fle)
>>  	return -1;
>>  }
>>  
>> +int recv_fd_from_peer(struct fdinfo_list_entry *fle)
>> +{
>> +	struct fdinfo_list_entry *tmp;
>> +	int fd, ret;
>> +
>> +	ret = recv_fds(fle->fe->fd, &fd, 1, NULL, (unsigned long *)&tmp);
>> +	if (ret)
>> +		return -1;
>> +
>> +	if (tmp != fle) {
>> +		pr_err("Received wrong fle\n");
> 
> How do you guarantee the order of receiving file descriptors?
> Descriptors are sent from different processes, how do you synchronize
> them?

The thing is this patch does not change logic. It even does not break tests.
We still have receive stage, and the patch is a preparation to a moment
when order is changed.

Order processing is in other patch: "[09/30] files: Allow to receive further fds".
It prepares recv_fd_from_peer() to make a deal with multiply received fles. But even there
it's unused, it's a preparation.

Real use of single transport_fd for sending and receiving is in "[10/30] files: Make sending fds to peers async".
Per-fd transport fds are killed there.

>> +		return -1;
>> +	}
>> +
>> +	return fd;
>> +}
>> +
>>  int send_fd_to_peer(int fd, struct fdinfo_list_entry *fle, int sock)
>>  {
>>  	struct sockaddr_un saddr;
>> @@ -968,7 +985,7 @@ int send_fd_to_peer(int fd, struct fdinfo_list_entry *fle, int sock)
>>  	transport_name_gen(&saddr, &len,
>>  			futex_get(&fle->real_pid), fle->fe->fd);
>>  	pr_info("\t\tSend fd %d to %s\n", fd, saddr.sun_path + 1);
>> -	return send_fd(sock, &saddr, len, fd);
>> +	return send_fds(sock, &saddr, len, &fd, 1, false, (unsigned long *)&fle);
>>  }
>>  
>>  static int send_fd_to_self(int fd, struct fdinfo_list_entry *fle, int sock)
>> @@ -1078,7 +1095,7 @@ static int receive_fd(int pid, struct fdinfo_list_entry *fle)
>>  
>>  	pr_info("\tReceive fd for %d\n", fle->fe->fd);
>>  
>> -	tmp = recv_fd(fle->fe->fd);
>> +	tmp = recv_fd_from_peer(fle);
>>  	if (tmp < 0) {
>>  		pr_err("Can't get fd %d\n", tmp);
>>  		return -1;
>> diff --git a/criu/include/files.h b/criu/include/files.h
>> index 2cd1a67..457cc46 100644
>> --- a/criu/include/files.h
>> +++ b/criu/include/files.h
>> @@ -148,6 +148,7 @@ extern int file_desc_add(struct file_desc *d, u32 id, struct file_desc_ops *ops)
>>  extern struct fdinfo_list_entry *file_master(struct file_desc *d);
>>  extern struct file_desc *find_file_desc_raw(int type, u32 id);
>>  
>> +extern int recv_fd_from_peer(struct fdinfo_list_entry *fle);
>>  extern int send_fd_to_peer(int fd, struct fdinfo_list_entry *fle, int sock);
>>  extern int restore_fown(int fd, FownEntry *fown);
>>  extern int rst_file_params(int fd, FownEntry *fown, int flags);
>> diff --git a/criu/pipes.c b/criu/pipes.c
>> index 9fc87bd..31f436e 100644
>> --- a/criu/pipes.c
>> +++ b/criu/pipes.c
>> @@ -237,7 +237,7 @@ static int recv_pipe_fd(struct pipe_info *pi)
>>  
>>  	pr_info("\tWaiting fd for %d\n", fd);
>>  
>> -	tmp = recv_fd(fd);
>> +	tmp = recv_fd_from_peer(fle);
>>  	if (tmp < 0) {
>>  		pr_err("Can't get fd %d\n", tmp);
>>  		return -1;
>> diff --git a/criu/sk-unix.c b/criu/sk-unix.c
>> index 6a1a532..7d9728a 100644
>> --- a/criu/sk-unix.c
>> +++ b/criu/sk-unix.c
>> @@ -1096,7 +1096,7 @@ static int open_unixsk_pair_slave(struct unix_sk_info *ui)
>>  	pr_info("Opening pair slave (id %#x ino %#x peer %#x) on %d\n",
>>  			ui->ue->id, ui->ue->ino, ui->ue->peer, fle->fe->fd);
>>  
>> -	sk = recv_fd(fle->fe->fd);
>> +	sk = recv_fd_from_peer(fle);
>>  	if (sk < 0) {
>>  		pr_err("Can't recv pair slave\n");
>>  		return -1;
>> diff --git a/criu/tty.c b/criu/tty.c
>> index 7ec5b1f..3dc60cd 100644
>> --- a/criu/tty.c
>> +++ b/criu/tty.c
>> @@ -923,7 +923,7 @@ static int receive_tty(struct tty_info *info)
>>  	fle = file_master(&info->d);
>>  	pr_info("\tWaiting tty fd %d (pid %d)\n", fle->fe->fd, fle->pid);
>>  
>> -	fd = recv_fd(fle->fe->fd);
>> +	fd = recv_fd_from_peer(fle);
>>  	close(fle->fe->fd);
>>  	if (fd < 0) {
>>  		pr_err("Can't get fd %d\n", fd);
>>