[CRIU] [PATCH 1/5] pipe: don't create a tranport descriptor for inhereted pipes

[Andrew Vagin]

On Mon, Jul 13, 2015 at 03:15:43PM +0300, Pavel Emelyanov wrote:
> On 07/02/2015 12:47 PM, Andrey Vagin wrote:
> > Otherwise we can get an error like this:
> > 1: \t\tCreate transport fd /crtools-fd-1-5
> > ...
> > 1: Found id pipe:[122747] (fd 8) in inherit fd list
> > 1: File pipe:[122747] will be restored from fd 9 duped from inherit
> > 
> > 1: Error (util.c:131): fd 5 already in use (called at files.c:872)
> 
> Frankly, I don't get what this error means. Can you share more details on it, please?

When we have a few descriptors which is associated with one inherited
pipe, we create a transport sockets for all descriptors except one. It's
our standard engine to restore file descriptors. But when we restore
inhereted fd, we alread have a descriptors which can be used to restore
a pipe and we use it. The code which restore inhereted pipes knows
nothing about transport sockets and fails if a required descriptor is
busy.

> 
> > Signed-off-by: Andrey Vagin <avagin at openvz.org>
> > ---
> >  files.c |  3 +++
> >  pipes.c | 20 ++++++++++++--------
> >  2 files changed, 15 insertions(+), 8 deletions(-)
> > 
> > diff --git a/files.c b/files.c
> > index 4eeb988..3e69be7 100644
> > --- a/files.c
> > +++ b/files.c
> > @@ -1394,6 +1394,9 @@ bool inherited_fd(struct file_desc *d, int *fd_p)
> >  	if (i_fd < 0)
> >  		return false;
> >  
> > +	if (fd_p == NULL)
> > +		return true;
> > +
> >  	*fd_p = dup(i_fd);
> >  	if (*fd_p < 0)
> >  		pr_perror("Inherit fd DUP failed");
> > diff --git a/pipes.c b/pipes.c
> > index 7590472..62f550c 100644
> > --- a/pipes.c
> > +++ b/pipes.c
> > @@ -393,18 +393,22 @@ static int collect_one_pipe(void *o, ProtobufCMessage *base)
> >  	pr_info("Collected pipe entry ID %#x PIPE ID %#x\n",
> >  			pi->pe->id, pi->pe->pipe_id);
> >  
> > -	list_for_each_entry(tmp, &pipes, list)
> > -		if (pi->pe->pipe_id == tmp->pe->pipe_id)
> > -			break;
> > +	if (file_desc_add(&pi->d, pi->pe->id, &pipe_desc_ops))
> > +		return -1;
> >  
> > -	if (&tmp->list == &pipes)
> > -		INIT_LIST_HEAD(&pi->pipe_list);
> > -	else
> > -		list_add(&pi->pipe_list, &tmp->pipe_list);
> > +	INIT_LIST_HEAD(&pi->pipe_list);
> > +	if (!inherited_fd(&pi->d, NULL)) {
> > +		list_for_each_entry(tmp, &pipes, list)
> > +			if (pi->pe->pipe_id == tmp->pe->pipe_id)
> > +				break;
> > +
> > +		if (&tmp->list != &pipes)
> > +			list_add(&pi->pipe_list, &tmp->pipe_list);
> > +	}
> >  
> >  	list_add_tail(&pi->list, &pipes);
> > -	return file_desc_add(&pi->d, pi->pe->id, &pipe_desc_ops);
> >  
> > +	return 0;
> >  }
> >  
> >  struct collect_image_info pipe_cinfo = {
> > 
>