[CRIU] [PATCH v3 45/55] ns: Add usernsd signal handler

[Andrei Vagin]

Could you explain in each commit message why we need these changes and
what they do?

On Mon, Apr 10, 2017 at 11:22:33AM +0300, Kirill Tkhai wrote:
> v3: pr_err() -> pr_info()
> v2: New
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/namespaces.c |   34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/criu/namespaces.c b/criu/namespaces.c
> index 3562f9a2a..8bc876465 100644
> --- a/criu/namespaces.c
> +++ b/criu/namespaces.c
> @@ -14,6 +14,7 @@
>  #include <limits.h>
>  #include <errno.h>
>  #include <sys/ioctl.h>
> +#include <sys/ptrace.h>
>  
>  #include "page.h"
>  #include "rst-malloc.h"
> @@ -24,6 +25,7 @@
>  #include "mount.h"
>  #include "pstree.h"
>  #include "namespaces.h"
> +#include "restore.h"
>  #include "net.h"
>  #include "cgroup.h"
>  #include "kerndat.h"
> @@ -1508,6 +1510,33 @@ static void unsc_msg_pid_fd(struct unsc_msg *um, pid_t *pid, int *fd)
>  	}
>  }
>  
> +static void usernsd_handler(int signal, siginfo_t *siginfo, void *data)
> +{
> +	pid_t pid = siginfo->si_pid;
> +	int status;
> +	int exit;
> +
> +	if (siginfo->si_code == CLD_TRAPPED && siginfo->si_status == SIGCHLD) {
> +		/* The usernsd is ptraced. Allow it to handle SIGCHLD */
> +		ptrace(PTRACE_CONT, siginfo->si_pid, 0, SIGCHLD);

Who ptraces usernsd? Signals can be merged, so you have to user wait4 to
get all pids?
> +		return;
> +	}
> +
> +	while (pid) {
> +		pid = waitpid(-1, &status, WNOHANG);
> +		if (pid <= 0)
> +			return;
> +
> +		exit = WIFEXITED(status);
> +		status = exit ? WEXITSTATUS(status) : WTERMSIG(status);
> +		if (status) {
> +			futex_abort_and_wake(&task_entries->nr_in_progress);
> +			pr_err("%d finished abnormal\n", pid);
> +		} else
> +			pr_info("%d exited normally\n", pid);
> +	}
> +}
> +
>  static int usernsd(int sk)
>  {
>  	struct sockaddr_un addr;
> @@ -1537,6 +1566,11 @@ static int usernsd(int sk)
>  		return -1;
>  	}
>  
> +	if (criu_signals_setup(usernsd_handler) < 0) {
> +		pr_err("Can't setup handler\n");
> +		return -1;
> +	}
> +
>  	while (1) {
>  		struct unsc_msg um;
>  		static char msg[MAX_UNSFD_MSG_SIZE];
>