Re: [PATCH 04/14] nstool: Split some command line parsing and socket setup to subcommands

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 6 Apr 2023 12:31:55 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Apr 05, 2023 at 01:58:00PM +0200, Stefano Brivio wrote:
>
> [...]
>
> > I didn't spot this earlier, but... does it really make sense to wait in
> > cmd_pid(), also on ENOENT, rather than making 'hold' return only once
> > the socket is ready?  
> 
> So, this is a consequence of the fact that the holder doesn't move
> into the background itself - it just sits in the foreground until
> terminated.  That means that the typical usecase puts it into the
> background from the shell with &, which in turn means that when we
> reach the next shell command the socket may not be ready - or not even
> created.
> 
> One of the things I had in mind for a hypothetical "nstool unshare"
> would be to avoid this and have it background itself once the socket
> is ready.

Ah, sure, it makes sense now.

> > I don't think it would be outrageous to have
> > 'nstool pid' failing if the holding process doesn't exist.
> > 
> > Admittely, I'm biased by the few hundreds of times I needed to
> > 'killall -9 nsholder' in the past months. :)  
> 
> So... I agree that's irritating, I've done it a similar number of
> times.  However, I don't think that's really related to the question
> above - in my experience it's always been the holder process that's
> hung around, not something waiting on a holder.

Yes, same here, but it's something I file under the same category (I
don't remember why nsholder would hang, you probably explained at some
point...).

> > >  	rc = getsockopt(fd, SOL_SOCKET, SO_PEERCRED,
> > >  			&peercred, &optlen);
> > >  	if (rc < 0)
> > > -		die("getsockopet(SO_PEERCRED): %s\n", strerror(errno));
> > > +		die("getsockopet(SO_PEERCRED) %s: %s\n",
> > > +		    sockpath, strerror(errno));
> > >  
> > >  	close(fd);
> > >  
> > >  	printf("%d\n", peercred.pid);
> > >  }
> > >  
> > > -static void stop(int fd, const struct sockaddr_un *addr)
> > > +static void cmd_stop(int argc, char *argv[])
> > >  {
> > > -	int rc;
> > > +	const char *sockpath = argv[1];
> > > +	int fd, rc;
> > >  	char buf = 'Q';
> > >  
> > > -	rc = connect(fd, (struct sockaddr *)addr, sizeof(*addr));
> > > -	if (rc < 0)
> > > -		die("connect(): %s\n", strerror(errno));
> > > +	if (argc != 2)
> > > +		usage();
> > > +
> > > +	fd = connect_ctl(sockpath, false);
> > >  
> > >  	rc = write(fd, &buf, sizeof(buf));  
> > 
> > Unrelated: a compound literal would make this more readable.  
> 
> Uh.. I don't see where a compound literal would even go here.

I meant:

	rc = write(fd, &(char){ 'Q' }, 1);

...so that one doesn't need to look at 'buf'. nstool is C99 anyway.

-- 
Stefano