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Commit 6ad53df6 authored by Rom Lemarchand's avatar Rom Lemarchand
Browse files

liblogwrap: use POLLHUP flag to check when a child dies 

Replace the old signal handling mechanism with a check of POLLHUP
to check when the child has died.

See http://b/8333626

Change-Id: Ic9909b6660b1c3d1ed3015568b1a1ee1c25afe20
parent 7bce39ca

logwrapper/logwrap.c

+49 −102
Original line number Diff line number Diff line
@@ -17,7 +17,6 @@ 
#include <string.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <signal.h>

#include <poll.h>

#include <sys/wait.h>

#include <stdio.h>
@@ -35,7 +34,6 @@ 


#define ARRAY_SIZE(x)   (sizeof(x) / sizeof(*(x)))



static int signal_fd_write;

static pthread_mutex_t fd_mutex = PTHREAD_MUTEX_INITIALIZER;



#define ERROR(fmt, args...)                                                   \
@@ -50,45 +48,34 @@ do { \ 
    _exit(-1);                                                                \

} while(0)



static int parent(const char *tag, int parent_read, int signal_fd, pid_t pid,

        int *chld_sts, bool logwrap) {

static int parent(const char *tag, int parent_read, pid_t pid, int *chld_sts,

        bool logwrap) {

    int status = 0;

    char buffer[4096];

    struct pollfd poll_fds[] = {

        [0] = {

            .fd = signal_fd,

            .events = POLLIN,

        },

        [1] = {

            .fd = parent_read,

            .events = POLLIN,

        },

    };

    int rc = 0;

    sigset_t chldset;



    int a = 0;  // start index of unprocessed data

    int b = 0;  // end index of unprocessed data

    int sz;

    bool remote_hung = false;

    bool found_child = false;



    char *btag = basename(tag);

    if (!btag) btag = (char*) tag;



    sigemptyset(&chldset);

    sigaddset(&chldset, SIGCHLD);

    pthread_sigmask(SIG_UNBLOCK, &chldset, NULL);



    while (!found_child) {

        if (TEMP_FAILURE_RETRY(poll(poll_fds, remote_hung ? 1 : 2, -1)) < 0) {

        if (TEMP_FAILURE_RETRY(poll(poll_fds, ARRAY_SIZE(poll_fds), -1)) < 0) {

            ERROR("poll failed\n");

            rc = -1;

            goto err_poll;

        }



        if (!remote_hung) {

            if (poll_fds[1].revents & POLLIN) {

        if (poll_fds[0].revents & POLLIN) {

            sz = read(parent_read, &buffer[b], sizeof(buffer) - 1 - b);



            sz += b;
@@ -121,23 +108,17 @@ static int parent(const char *tag, int parent_read, int signal_fd, pid_t pid, 
            }

        }



            if (poll_fds[1].revents & POLLHUP) {

                remote_hung = true;

            }

        }



        if (poll_fds[0].revents & POLLIN) {

            char tmp[32];

        if (poll_fds[0].revents & POLLHUP) {

            int ret;



            read(signal_fd, tmp, sizeof(tmp));

            while (!found_child) {

                ret = TEMP_FAILURE_RETRY(waitpid(-1, &status, WNOHANG));



                if (ret <= 0)

                    break;



                found_child = (pid == ret);

            ret = waitpid(pid, &status, WNOHANG);

            if (ret < 0) {

                rc = errno;

                ALOG(LOG_ERROR, "logwrap", "waitpid failed with %s\n", strerror(errno));

                goto err_waitpid;

            }

            if (ret > 0) {

                found_child = true;

            }

        }

    }
@@ -171,6 +152,7 @@ static int parent(const char *tag, int parent_read, int signal_fd, pid_t pid, 
      }

    }



err_waitpid:

err_poll:

    return rc;

}
@@ -187,23 +169,16 @@ static void child(int argc, char* argv[], bool logwrap) { 
    }

}



static void sigchld_handler(int sig) {

    write(signal_fd_write, &sig, 1);

}



int android_fork_execvp(int argc, char* argv[], int *status, bool ignore_int_quit,

        bool logwrap) {

    pid_t pid;

    int parent_ptty;

    int child_ptty;

    char *child_devname = NULL;

    struct sigaction chldact;

    struct sigaction oldchldact;

    struct sigaction intact;

    struct sigaction quitact;

    sigset_t blockset;

    sigset_t oldset;

    int sockets[2];

    int rc = 0;



    rc = pthread_mutex_lock(&fd_mutex);
@@ -227,14 +202,21 @@ int android_fork_execvp(int argc, char* argv[], int *status, bool ignore_int_qui 
        goto err_ptty;

    }



    child_ptty = open(child_devname, O_RDWR);

    if (child_ptty < 0) {

        ERROR("Cannot open child_ptty\n");

        rc = -1;

        goto err_child_ptty;

    }



    sigemptyset(&blockset);

    sigaddset(&blockset, SIGINT);

    sigaddset(&blockset, SIGQUIT);

    sigaddset(&blockset, SIGCHLD);

    pthread_sigmask(SIG_BLOCK, &blockset, &oldset);



    pid = fork();

    if (pid < 0) {

        close(child_ptty);

        ERROR("Failed to fork\n");

        rc = -1;

        goto err_fork;
@@ -243,12 +225,6 @@ int android_fork_execvp(int argc, char* argv[], int *status, bool ignore_int_qui 
        pthread_sigmask(SIG_SETMASK, &oldset, NULL);

        close(parent_ptty);



        child_ptty = open(child_devname, O_RDWR);

        if (child_ptty < 0) {

            FATAL_CHILD("Problem with child ptty\n");

            return -1;

        }



        // redirect stdout and stderr

        dup2(child_ptty, 1);

        dup2(child_ptty, 2);
@@ -256,55 +232,26 @@ int android_fork_execvp(int argc, char* argv[], int *status, bool ignore_int_qui 


        child(argc, argv, logwrap);

    } else {

        close(child_ptty);

        if (ignore_int_quit) {

            struct sigaction ignact;



        memset(&chldact, 0, sizeof(chldact));

        chldact.sa_handler = sigchld_handler;

        chldact.sa_flags = SA_NOCLDSTOP;



        sigaction(SIGCHLD, &chldact, &oldchldact);

        if ((!(oldchldact.sa_flags & SA_SIGINFO) &&

                oldchldact.sa_handler != SIG_DFL &&

                oldchldact.sa_handler != SIG_IGN) ||

                ((oldchldact.sa_flags & SA_SIGINFO) &&

                oldchldact.sa_sigaction != NULL)) {

            ALOG(LOG_WARN, "logwrapper", "logwrap replaced the SIGCHLD "

                    "handler and might cause interaction issues");

        }



        if (ignore_int_quit) {

            memset(&ignact, 0, sizeof(ignact));

            ignact.sa_handler = SIG_IGN;

            sigaction(SIGINT, &ignact, &intact);

            sigaction(SIGQUIT, &ignact, &quitact);

        }



        rc = socketpair(AF_UNIX, SOCK_STREAM, 0, sockets);

        if (rc == -1) {

            ERROR("socketpair failed: %s\n", strerror(errno));

            goto err_socketpair;

        }



        fcntl(sockets[0], F_SETFD, FD_CLOEXEC);

        fcntl(sockets[0], F_SETFL, O_NONBLOCK);

        fcntl(sockets[1], F_SETFD, FD_CLOEXEC);

        fcntl(sockets[1], F_SETFL, O_NONBLOCK);



        signal_fd_write = sockets[0];



        rc = parent(argv[0], parent_ptty, sockets[1], pid, status, logwrap);

        rc = parent(argv[0], parent_ptty, pid, status, logwrap);

    }



    close(sockets[0]);

    close(sockets[1]);

err_socketpair:

    if (ignore_int_quit) {

        sigaction(SIGINT, &intact, NULL);

        sigaction(SIGQUIT, &quitact, NULL);

    }

    sigaction(SIGCHLD, &oldchldact, NULL);

err_fork:

    pthread_sigmask(SIG_SETMASK, &oldset, NULL);

err_child_ptty:

err_ptty:

    close(parent_ptty);

err_open: