[CRIU] Re: [PATCH 5/5] util: move network socket to free FD during restore

[Pavel Emelyanov]

On 08/22/2012 01:26 PM, Adrian Reber wrote:
> On Tue, Aug 21, 2012 at 08:39:24PM +0400, Pavel Emelyanov wrote:
>> On 08/21/2012 07:20 PM, Adrian Reber wrote:
>>> The socket listening on the network has to be moved during the
>>> restore so that it does not collide with FDs which are trying
>>> to be restored.
>>>
>>> Signed-off-by: Adrian Reber <adrian at lisas.de>
>>> ---
>>>  image.c           |    7 +++++++
>>>  include/crtools.h |    1 +
>>>  util.c            |    9 +++++++++
>>>  3 files changed, 17 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/image.c b/image.c
>>> index 969017a..0d84c5c 100644
>>> --- a/image.c
>>> +++ b/image.c
>>> @@ -366,3 +366,10 @@ int reopen_listen_socket()
>>>  		return open_listen_socket(network_host, network_port);
>>>  	return 0;
>>>  }
>>> +
>>> +void update_listen_socket(int fd)
>>> +{
>>> +	if (sockfd == -1)
>>> +		return;
>>> +	sockfd = fd;
>>> +}
>>> diff --git a/include/crtools.h b/include/crtools.h
>>> index c092802..f056327 100644
>>> --- a/include/crtools.h
>>> +++ b/include/crtools.h
>>> @@ -135,6 +135,7 @@ extern void close_image_dir(void);
>>>  extern int open_listen_socket(char *host, int port);
>>>  extern void close_listen_socket();
>>>  extern int reopen_listen_socket();
>>> +extern void update_listen_socket(int fd);
>>>  
>>>  int open_image(int type, unsigned long flags, ...);
>>>  #define open_image_ro(type, ...) open_image(type, O_RDONLY, ##__VA_ARGS__)
>>> diff --git a/util.c b/util.c
>>> index 4969e8d..91795d1 100644
>>> --- a/util.c
>>> +++ b/util.c
>>> @@ -83,6 +83,15 @@ int reopen_fd_as_safe(char *file, int line, int new_fd, int old_fd, bool allow_r
>>>  	if (old_fd != new_fd) {
>>>  
>>>  		if (!allow_reuse_fd) {
>>> +			/* see if we are running a network migration */
>>> +			tmp = open_listen_socket(NULL, 0);
>>> +			if (tmp != -1) {
>>> +				int tmp2;
>>> +				/* yes, network socket is open; let's move it */
>>> +				tmp2 = fcntl(tmp, F_DUPFD, new_fd);
>>> +				update_listen_socket(tmp2);
>>> +				close(tmp);
>>
>> You should just place a call to move_img_fd to proper place to prevent
>> it from being overwritten by the restore fd.
> 
> The problem with move_img_fd() was that it moved my socket to FD 1 and
> then the program to be restored segfaulted. Moving it with fcntl moves
> it to a descriptor with a higher number and does the "right thing".
> 
> What is the correct way to use move_img_fd() without blocking of the
> lower FDs?

You should call it before restoring each fd. It will occupy the first free fd.

> 		Adrian
> .
>