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

On Thu, 6 Apr 2023 12:31:55 +1000
David Gibson <david(a)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