logwrapper/logwrap.c

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <string.h>
#include <sys/types.h>
#include <sys/signalfd.h>
#include <signal.h>
#include <poll.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>

#include <logwrap/logwrap.h>
#include "private/android_filesystem_config.h"
#include "cutils/log.h"

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

static int fatal(const char *msg) {
    fprintf(stderr, "%s", msg);
    ALOG(LOG_ERROR, "logwrapper", "%s", msg);
    return -1;
}

static int parent(const char *tag, int parent_read, int signal_fd, pid_t pid,
        int *chld_sts) {
    int status;
    char buffer[4096];
    struct pollfd poll_fds[] = {
        [0] = {
            .fd = parent_read,
            .events = POLLIN,
        },
        [1] = {
            .fd = signal_fd,
            .events = POLLIN,
        },
    };

    int a = 0;  // start index of unprocessed data
    int b = 0;  // end index of unprocessed data
    int sz;

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

    while (1) {
        if (poll(poll_fds, ARRAY_SIZE(poll_fds), -1) <= 0) {
            return fatal("poll failed\n");
        }

        if (poll_fds[0].revents & POLLIN) {
            sz = read(parent_read, &buffer[b], sizeof(buffer) - 1 - b);

            sz += b;
            // Log one line at a time
            for (b = 0; b < sz; b++) {
                if (buffer[b] == '\r') {
                    buffer[b] = '\0';
                } else if (buffer[b] == '\n') {
                    buffer[b] = '\0';
                    ALOG(LOG_INFO, btag, "%s", &buffer[a]);
                    a = b + 1;
                }
            }

            if (a == 0 && b == sizeof(buffer) - 1) {
                // buffer is full, flush
                buffer[b] = '\0';
                ALOG(LOG_INFO, btag, "%s", &buffer[a]);
                b = 0;
            } else if (a != b) {
                // Keep left-overs
                b -= a;
                memmove(buffer, &buffer[a], b);
                a = 0;
            } else {
                a = 0;
                b = 0;
            }
        }

        if (poll_fds[1].revents & POLLIN) {
            struct signalfd_siginfo sfd_info;
            pid_t wpid;

            // Clear all pending signals before reading the child's status
            while (read(signal_fd, &sfd_info, sizeof(sfd_info)) > 0) {
                if ((pid_t)sfd_info.ssi_pid != pid)
                    ALOG(LOG_WARN, "logwrapper", "cleared SIGCHLD for pid %u\n",
                            sfd_info.ssi_pid);
            }
            wpid = waitpid(pid, &status, WNOHANG);
            if (wpid > 0)
                break;
        }
    }

    // Flush remaining data
    if (a != b) {
        buffer[b] = '\0';
        ALOG(LOG_INFO, btag, "%s", &buffer[a]);
    }

    if (WIFEXITED(status)) {
        if (WEXITSTATUS(status))
            ALOG(LOG_INFO, "logwrapper", "%s terminated by exit(%d)", tag,
                    WEXITSTATUS(status));
    } else if (WIFSIGNALED(status)) {
        ALOG(LOG_INFO, "logwrapper", "%s terminated by signal %d", tag,
                WTERMSIG(status));
    } else if (WIFSTOPPED(status)) {
        ALOG(LOG_INFO, "logwrapper", "%s stopped by signal %d", tag,
                WSTOPSIG(status));
    }
    if (chld_sts != NULL)
        *chld_sts = status;

    return 0;
}

static void child(int argc, char* argv[]) {
    // create null terminated argv_child array
    char* argv_child[argc + 1];
    memcpy(argv_child, argv, argc * sizeof(char *));
    argv_child[argc] = NULL;

    if (execvp(argv_child[0], argv_child)) {
        ALOG(LOG_ERROR, "logwrapper",
            "executing %s failed: %s\n", argv_child[0], strerror(errno));
        exit(-1);
    }
}

int logwrap(int argc, char* argv[], int *status) {
    pid_t pid;

    int parent_ptty;
    int child_ptty;
    char *child_devname = NULL;
    sigset_t chldset;

    /* Use ptty instead of socketpair so that STDOUT is not buffered */
    parent_ptty = open("/dev/ptmx", O_RDWR);
    if (parent_ptty < 0) {
        return fatal("Cannot create parent ptty\n");
    }

    if (grantpt(parent_ptty) || unlockpt(parent_ptty) ||
            ((child_devname = (char*)ptsname(parent_ptty)) == 0)) {
        return fatal("Problem with /dev/ptmx\n");
    }

    sigemptyset(&chldset);
    sigaddset(&chldset, SIGCHLD);
    sigprocmask(SIG_BLOCK, &chldset, NULL);

    pid = fork();
    if (pid < 0) {
        close(parent_ptty);
        sigprocmask(SIG_UNBLOCK, &chldset, NULL);
        return fatal("Failed to fork\n");
    } else if (pid == 0) {
        close(parent_ptty);
        sigprocmask(SIG_UNBLOCK, &chldset, NULL);
        child_ptty = open(child_devname, O_RDWR);
        if (child_ptty < 0) {
            return fatal("Problem with child ptty\n");
        }

        // redirect stdout and stderr
        dup2(child_ptty, 1);
        dup2(child_ptty, 2);
        close(child_ptty);

        child(argc - 1, &argv[1]);
        return fatal("This should never happen\n");

    } else {
        int rc;
        int fd;

        fd = signalfd(-1, &chldset, SFD_NONBLOCK);
        if (fd == -1) {
            char msg[40];

            snprintf(msg, sizeof(msg), "signalfd failed: %d\n", errno);

            close(parent_ptty);
            sigprocmask(SIG_UNBLOCK, &chldset, NULL);
            return fatal(msg);
        }

        // switch user and group to "log"
        // this may fail if we are not root,
        // but in that case switching user/group is unnecessary
        setgid(AID_LOG);
        setuid(AID_LOG);

        rc = parent(argv[1], parent_ptty, fd, pid, status);
        close(parent_ptty);
        close(fd);

        sigprocmask(SIG_UNBLOCK, &chldset, NULL);

        return rc;
    }
}