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

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Apr 05, 2023 at 01:58:00PM +0200, Stefano Brivio wrote:
> On Tue,  4 Apr 2023 11:46:28 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > This will make it easier to differentiate the options to those commands
> > further in future.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  test/nstool.c | 102 +++++++++++++++++++++++++++++++++-----------------
> >  1 file changed, 68 insertions(+), 34 deletions(-)
> > 
> > diff --git a/test/nstool.c b/test/nstool.c
> > index 7e069b6..9ea7eeb 100644
> > --- a/test/nstool.c
> > +++ b/test/nstool.c
> > @@ -11,6 +11,7 @@
> >  #include <stdio.h>
> >  #include <stdlib.h>
> >  #include <string.h>
> > +#include <stdbool.h>
> >  #include <errno.h>
> >  #include <unistd.h>
> >  #include <sys/socket.h>
> > @@ -37,19 +38,55 @@ static void usage(void)
> >  	    "    terminate.\n");
> >  }
> >  
> > -static void hold(int fd, const struct sockaddr_un *addr)
> > +static int connect_ctl(const char * sockpath, bool wait)
> >  {
> > +	int fd = socket(AF_UNIX, SOCK_STREAM, PF_UNIX);
> > +	struct sockaddr_un addr = {
> > +		.sun_family = AF_UNIX,
> > +	};
> >  	int rc;
> >  
> > -	rc = bind(fd, (struct sockaddr *)addr, sizeof(*addr));
> > +	if (fd < 0)
> > +		die("socket(): %s\n", strerror(errno));
> 
> Unrelated: it would be nice if die() added newlines eventually.

Sure, but as you say unrelated.

> > +
> > +	strncpy(addr.sun_path, sockpath, UNIX_PATH_MAX);
> > +
> > +	do {
> > +		rc = connect(fd, (struct sockaddr *)&addr, sizeof(addr));
> > +		if (rc < 0 &&
> > +		    (!wait || (errno != ENOENT && errno != ECONNREFUSED)))
> > +			die("connect() to %s: %s\n", sockpath, strerror(errno));
> 
> A (1ms?) delay would be nice to have here -- it's almost a busyloop,
> connect() fails fast.

Yeah, I guess so.  That's not new, it was already like that in
"nsholder pid", so I think something to fix separately.

> > +	} while (rc < 0);
> > +
> > +	return fd;
> > +}
> > +
> > +static void cmd_hold(int argc, char *argv[])
> > +{
> > +	int fd = socket(AF_UNIX, SOCK_STREAM, PF_UNIX);
> > +	struct sockaddr_un addr = {
> > +		.sun_family = AF_UNIX,
> > +	};
> > +	const char *sockpath = argv[1];
> > +	int rc;
> > +
> > +	if (argc != 2)
> > +		usage();
> > +
> > +	if (fd < 0)
> > +		die("socket(): %s\n", strerror(errno));
> > +
> > +	strncpy(addr.sun_path, sockpath, UNIX_PATH_MAX);
> > +
> > +	rc = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
> >  	if (rc < 0)
> > -		die("bind(): %s\n", strerror(errno));
> > +		die("bind() to %s: %s\n", sockpath, strerror(errno));
> >  
> >  	rc = listen(fd, 0);
> >  	if (rc < 0)
> > -		die("listen(): %s\n", strerror(errno));
> > +		die("listen() on %s: %s\n", sockpath, strerror(errno));
> >  
> > -	printf("nstool: local PID=%d  local UID=%u  local GID=%u\n",
> > +	printf("nstool hold: local PID=%d  local UID=%u  local GID=%u\n",
> >  	       getpid(), getuid(), getgid());
> >  	do {
> >  		int afd = accept(fd, NULL, NULL);
> > @@ -63,71 +100,68 @@ static void hold(int fd, const struct sockaddr_un *addr)
> >  			die("read(): %s\n", strerror(errno));
> >  	} while (rc == 0);
> >  
> > -	unlink(addr->sun_path);
> > +	unlink(sockpath);
> >  }
> >  
> > -static void pid(int fd, const struct sockaddr_un *addr)
> > +static void cmd_pid(int argc, char *argv[])
> >  {
> > -	int rc;
> > +	const char *sockpath = argv[1];
> >  	struct ucred peercred;
> >  	socklen_t optlen = sizeof(peercred);
> > +	int fd, rc;
> >  
> > -	do {
> > -		rc = connect(fd, (struct sockaddr *)addr, sizeof(*addr));
> > -		if (rc < 0 && errno != ENOENT && errno != ECONNREFUSED)
> > -			die("connect(): %s\n", strerror(errno));
> > -	} while (rc < 0);
> > +	if (argc != 2)
> > +		usage();
> > +
> > +	fd = connect_ctl(sockpath, true);
> 
> 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.

> 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.


> >  	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.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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