Re: [PATCH 09/14] nstool: Add nstool exec command to execute commands in an nstool namespace

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

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On Wed, Apr 05, 2023 at 01:58:54PM +0200, Stefano Brivio wrote:
> On Tue,  4 Apr 2023 11:46:33 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > This combines nstool info -pw <sock> with nsenter with various options for
> > a more convenient and less verbose of entering existing nstool managed
> > namespaces.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  test/nstool.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 137 insertions(+), 2 deletions(-)
> > 
> > diff --git a/test/nstool.c b/test/nstool.c
> > index 5681ce8..25079aa 100644
> > --- a/test/nstool.c
> > +++ b/test/nstool.c
> > @@ -17,7 +17,9 @@
> >  #include <unistd.h>
> >  #include <getopt.h>
> >  #include <stdarg.h>
> > +#include <fcntl.h>
> >  #include <sys/socket.h>
> > +#include <sys/wait.h>
> >  #include <linux/un.h>
> >  #include <linux/limits.h>
> >  #include <sched.h>
> > @@ -75,6 +77,9 @@ static void usage(void)
> >  	    "    socket at SOCK\n"
> >  	    "      -p    Print just the holder's PID as seen by the caller\n"
> >  	    "      -w    Retry connecting to SOCK until it is ready\n"
> > +	    "  nstool exec SOCK [COMMAND [ARGS...]]\n"
> > +	    "    Execute command or shell in the namespaces of the nstool hold\n"
> > +	    "    with control socket at SOCK\n"
> >  	    "  nstool stop SOCK\n"
> >  	    "    Instruct the nstool hold with control socket at SOCK to\n"
> >  	    "    terminate.\n");
> > @@ -84,7 +89,7 @@ static int connect_ctl(const char *sockpath, bool wait,
> >  		       struct holder_info *info,
> >  		       struct ucred *peercred)
> >  {
> > -	int fd = socket(AF_UNIX, SOCK_STREAM, PF_UNIX);
> > +	int fd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, PF_UNIX);
> >  	struct sockaddr_un addr = {
> >  		.sun_family = AF_UNIX,
> >  	};
> > @@ -132,7 +137,7 @@ static int connect_ctl(const char *sockpath, bool wait,
> >  
> >  static void cmd_hold(int argc, char *argv[])
> >  {
> > -	int fd = socket(AF_UNIX, SOCK_STREAM, PF_UNIX);
> > +	int fd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, PF_UNIX);
> >  	struct sockaddr_un addr = {
> >  		.sun_family = AF_UNIX,
> >  	};
> > @@ -301,6 +306,134 @@ static void cmd_info(int argc, char *argv[])
> >  	}
> >  }
> >  
> > +static int openns(const char *fmt, ...)
> > +{
> > +	char nspath[PATH_MAX];
> > +	va_list ap;
> > +	int fd;
> > +
> > +	va_start(ap, fmt);
> > +	if (vsnprintf(nspath, sizeof(nspath), fmt, ap) >= PATH_MAX)
> > +		die("Truncated path \"%s\"\n", nspath);
> > +	va_end(ap);
> > +
> > +	fd = open(nspath, O_RDONLY | O_CLOEXEC);
> > +	if (fd < 0)
> > +		die("open() %s: %s\n", nspath, strerror(errno));
> > +
> > +	return fd;
> > +}
> > +
> > +static void wait_for_child(pid_t pid)
> > +{
> > +	int status;
> > +
> > +	/* Match the child's exit status, if possible */
> > +	for (;;) {
> > +		pid_t rc;
> > +
> > +                rc = waitpid(pid, &status, WUNTRACED);
> > +		if (rc < 0)
> > +			die("waitpid() on %d: %s\n", pid, strerror(errno));
> > +		if (rc != pid)
> > +			die("waitpid() on %d returned %d", pid, rc);
> > +                if (WIFSTOPPED(status)) {
> > +                        /* Stop the parent to patch */
> > +                        kill(getpid(), SIGSTOP);
> > +			/* We must have resumed, resume the child */
> > +                        kill(pid, SIGCONT);
> > +			continue;
> > +                }
> > +
> > +		break;
> > +        }
> > +
> > +        if (WIFEXITED(status))
> > +                exit(WEXITSTATUS(status));
> > +	else if (WIFSIGNALED(status))
> > +                kill(getpid(), WTERMSIG(status));
> 
> An alternative could be what pasta_child_handler() does on
> WIFSIGNALED(status) -- I don't actually have a preference between the
> two.

Right.  The idiom above I copied from unshare and nsenter in
util-linux.  Seems marginally more thorough than the 128+ trick.

> > +
> > +	die("Unexpected status for child %d\n", pid);
> 
> Weird indentation in this function.

Ugh, yes.  I think I did a copy paste at some point that introduced a
bunch of spaces where there should be tabs.  Fixing.

-- 
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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