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

[Andrei Vagin]

On Wed, Apr 26, 2017 at 05:15:39PM +0300, Kirill Tkhai wrote:
> On 26.04.2017 10:47, Andrei Vagin wrote:
> > On Tue, Apr 25, 2017 at 03:14:33PM +0300, Kirill Tkhai wrote:
> >>
> >> On 25.04.2017 08:34, Andrei Vagin wrote:
> >>> Could you explain in each commit message why we need these changes and
> >>> what they do?
> >>
> >> ns: Add usernsd signal handler
> >>
> >> Handler to catch exited children of usernsd.
> >> This will be used in next patches to watch
> >> for pid_ns helpers exit.
> >>
> >> v3: pr_err() -> pr_info()
> >> v2: New
> >>
> >> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> >>
> >>>
> >>> 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?
> > 
> > Pls, tell something about this ^^^^
> 
> Ah, I did't see this, sorry.
> 
> I though, when we're tracing criu, we're tracing all its processes. Than, why we do
> the following in sigchld_handler()?

it is for --restore-sibling
> 
>         if (!current && siginfo->si_code == CLD_TRAPPED &&
>                                 siginfo->si_status == SIGCHLD) {
>                 /* The root task is ptraced. Allow it to handle SIGCHLD */
>                 ptrace(PTRACE_CONT, siginfo->si_pid, 0, SIGCHLD);
>                 return;
>         }
>  
> >>>> +		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];
> >>>>