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

[Stefano Brivio <sbrivio@redhat.com>]

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.

> +
> +	die("Unexpected status for child %d\n", pid);

Weird indentation in this function.

-- 
Stefano