qemuhacks.c

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/*
 * Copyright (c) 2014 The University of Utah
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <signal.h>
#include <dlfcn.h>

static void *(*real_mmap)(void *addr,size_t length,int prot,int flags,
              int fd,off_t offset) = NULL;
static int (*real_unlink)(const char *name) = NULL;
static int (*real_atexit)(void (*function)(void)) = NULL;
static int (*real_sigaction)(int signum,const struct sigaction *act,
                 struct sigaction *oldact) = NULL;

static char **files = NULL;
static unsigned int files_size = 0;

static void (*qemu_sigint_handler)(int signo,siginfo_t *siginfo,void *c) = NULL;
static void (*qemu_sigterm_handler)(int signo,siginfo_t *siginfo,void *c) = NULL;
static void (*qemu_sighup_handler)(int signo,siginfo_t *siginfo,void *c) = NULL;

static int use_atexit = 0;
static int use_sig_override = 1;
static int no_cleanup = 0;

static void cleanup(void) {
    unsigned int i;

    for (i = 0; i < files_size; ++i) {
    real_unlink(files[i]);
    free(files[i]);
    }

    free(files);
}

/*
 * QEMU on POSIX OSes catches SIGINT, SIGHUP, SIGTERM, and dies.  This
 * is both the internal and external kill mechanism (i.e., if the
 * machine shuts itself down).  We know the machine is going to die at
 * this point, so cleanup, then call its sighandler!
 */
static void sig_override_handler(int signal,siginfo_t *info,void *x) {
    cleanup();
    if (signal == SIGINT)
    qemu_sigint_handler(signal,info,x);
    if (signal == SIGTERM)
    qemu_sigterm_handler(signal,info,x);
    if (signal == SIGHUP)
    qemu_sighup_handler(signal,info,x);;
}

/*
 * But unfortunately, QEMU unlink()s before it sets sighandlers.  So we
 * have to catch sigaction too.
 */
int sigaction(int signum,const struct sigaction *act,struct sigaction *oldact) {
    char *ev;
    struct sigaction ouract;

    if (!real_sigaction)
    real_sigaction = dlsym(RTLD_NEXT,"sigaction");

    ev = getenv("QEMU_NO_CLEANUP");
    if (ev) {
    no_cleanup = 1;
    use_atexit = 0;
    use_sig_override = 0;
    }
    ev = getenv("QEMU_USE_ATEXIT");
    if (ev) {
    use_atexit = 1;
    use_sig_override = 0;
    }
    ev = getenv("QEMU_USE_SIGOVERRIDE");
    if (ev) {
    use_atexit = 0;
    use_sig_override = 1;
    }

    if (no_cleanup)
    goto real;

    /*
     * Ok, intercept a few signals we know QEMU dies on.
     */
    if (signum == SIGINT || signum == SIGTERM || signum == SIGHUP) {
    memset(&ouract,0,sizeof(ouract));
    ouract.sa_sigaction = sig_override_handler;
    ouract.sa_mask = act->sa_mask;
    ouract.sa_flags = act->sa_flags;

    if (signum == SIGINT)
        qemu_sigint_handler = act->sa_sigaction;
    else if (signum == SIGTERM)
        qemu_sigterm_handler = act->sa_sigaction;
    else if (signum == SIGHUP)
        qemu_sighup_handler = act->sa_sigaction;

    return real_sigaction(signum,&ouract,oldact);
    }
    else
    goto real;

 real:
    return real_sigaction(signum,act,oldact);
}

/*
 * Wrap unlink to not unlink if @pathname starts with $QEMU_MEMPATH_PREFIX !
 */
int unlink(const char *pathname) {
    char *prefix;

    prefix = getenv("QEMU_MEMPATH_PREFIX");
    if (prefix && strncmp(prefix,pathname,strlen(prefix)) == 0) {
    errno = 0;
    files = realloc(files,files_size + 1);
    files[files_size] = strdup(pathname);
    ++files_size;
    if (files_size == 1) {
        char *ev;

        ev = getenv("QEMU_NO_CLEANUP");
        if (ev)
        no_cleanup = 1;
        ev = getenv("QEMU_USE_ATEXIT");
        if (ev)
        use_atexit = 1;
        ev = getenv("QEMU_USE_SIGOVERRIDE");
        if (ev)
        use_sig_override = 1;

        if (no_cleanup)
        ;
/*
 * This way doesn't work; we override sigaction() above.
 */
#if 0
        else if (use_sig_override) {
        struct sigaction act;
        struct sigaction oldact;

        memset(&act,0,sizeof(act));
        memset(&oldact,0,sizeof(oldact));

        act.sa_sigaction = sig_override_handler;
        act.sa_flags = SA_SIGINFO;

        sigaction(SIGTERM,&act,&oldact);
        if (0 && !oldact.sa_sigaction) {
            free(files[0]);
            free(files);
            files = NULL;
            files_size = 0;
            goto real;
        }
        else
            qemu_sighandler = oldact.sa_sigaction;

        if (oldact.sa_sigaction) {
            act.sa_flags = oldact.sa_flags;
            act.sa_mask = oldact.sa_mask;
        }

        sigaction(SIGINT,&act,NULL);
        sigaction(SIGHUP,&act,NULL);
        sigaction(SIGTERM,&act,NULL);
        }
#endif /* 0 */
        else {
        real_atexit = dlsym(RTLD_NEXT,"atexit");
        if (real_atexit)
            real_atexit(cleanup);
        }
    }
    return 0;
    }

    /* real: */
    if (!real_unlink)
    real_unlink = dlsym(RTLD_NEXT,"unlink");

    return real_unlink(pathname);
}

/*
 * Wrap mmap to share the mapping instead of privatize it if @fd's
 * pathname starts with $QEMU_MEMPATH_PREFIX .
 */
void *mmap(void *addr,size_t length,int prot,int flags,int fd,off_t offset) {
    char *prefix;

    if (fd <= 0)
    goto real;

    prefix = getenv("QEMU_MEMPATH_PREFIX");

    if (prefix) {
    char buf[32];
    char rbuf[256];
    snprintf(buf,sizeof(buf),"/proc/self/fd/%d",fd);
    if (readlink(buf,rbuf,sizeof(rbuf)) > 0
        && strncmp(prefix,rbuf,strlen(prefix)) == 0) {
        flags &= ~MAP_PRIVATE;
        flags |= MAP_SHARED;
    }
    }

 real:
    if (!real_mmap)
    real_mmap = dlsym(RTLD_NEXT,"mmap");
    return real_mmap(addr,length,prot,flags,fd,offset);
}