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

[Adrian Reber]

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?

		Adrian