xen/tools/xcutils/xc_save.c

/* 
 * This file is subject to the terms and conditions of the GNU General
 * Public License.  See the file "COPYING" in the main directory of
 * this archive for more details.
 *
 * Copyright (C) 2005 by Christian Limpach
 *
 */

#include <err.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <err.h>

#include <xs.h>
#include <xenctrl.h>
#include <xenguest.h>

static struct suspendinfo {
    xc_interface *xch;
    xc_evtchn *xce; /* event channel handle */
    int suspend_evtchn;
    int domid;
    unsigned int flags;
} si;

/**
 * Issue a suspend request through stdout, and receive the acknowledgement
 * from stdin.  This is handled by XendCheckpoint in the Python layer.
 */
static int compat_suspend(void)
{
    char ans[30];

    printf("suspend\n");
    fflush(stdout);

    return (fgets(ans, sizeof(ans), stdin) != NULL &&
            !strncmp(ans, "done\n", 5));
}

/**
 * Issue a suspend request to a dedicated event channel in the guest, and
 * receive the acknowledgement from the subscribe event channel. */
static int evtchn_suspend(void)
{
    int rc;

    rc = xc_evtchn_notify(si.xce, si.suspend_evtchn);
    if (rc < 0) {
        warnx("failed to notify suspend request channel: %d", rc);
        return 0;
    }

    if (xc_await_suspend(si.xch, si.xce, si.suspend_evtchn) < 0) {
        warnx("suspend failed");
        return 0;
    }

    /* notify xend that it can do device migration */
    printf("suspended\n");
    fflush(stdout);

    return 1;
}

static int suspend(void* data)
{
    unsigned long sx_state = 0;

    /* Cannot notify guest to shut itself down if it's in ACPI sleep state. */
    if (si.flags & XCFLAGS_HVM)
        xc_get_hvm_param(si.xch, si.domid,
                         HVM_PARAM_ACPI_S_STATE, &sx_state);

    if ((sx_state == 0) && (si.suspend_evtchn >= 0))
        return evtchn_suspend();

    return compat_suspend();
}

/* For HVM guests, there are two sources of dirty pages: the Xen shadow
 * log-dirty bitmap, which we get with a hypercall, and qemu's version.
 * The protocol for getting page-dirtying data from qemu uses a
 * double-buffered shared memory interface directly between xc_save and
 * qemu-dm. 
 *
 * xc_save calculates the size of the bitmaps and notifies qemu-dm 
 * through the store that it wants to share the bitmaps.  qemu-dm then 
 * starts filling in the 'active' buffer. 
 *
 * To change the buffers over, xc_save writes the other buffer number to
 * the store and waits for qemu to acknowledge that it is now writing to
 * the new active buffer.  xc_save can then process and clear the old
 * active buffer. */


static int switch_qemu_logdirty(int domid, unsigned int enable, void *data)
{
    struct xs_handle *xs;
    char *path, *p, *ret_str, *cmd_str, **watch;
    unsigned int len;
    struct timeval tv;
    fd_set fdset;

    if ((xs = xs_daemon_open()) == NULL)
        errx(1, "Couldn't contact xenstore");
    if (!(path = strdup("/local/domain/0/device-model/")))
        errx(1, "can't get domain path in store");
    if (!(path = realloc(path, strlen(path) 
                         + 10 
                         + strlen("/logdirty/cmd") + 1)))
        errx(1, "no memory for constructing xenstore path");
    snprintf(path + strlen(path), 11, "%i", domid);
    strcat(path, "/logdirty/");
    p = path + strlen(path);


    /* Watch for qemu's return value */
    strcpy(p, "ret");
    if (!xs_watch(xs, path, "qemu-logdirty-ret"))
        errx(1, "can't set watch in store (%s)\n", path);

    if (!(cmd_str = strdup( enable == 0 ? "disable" : "enable")))
        errx(1, "can't get logdirty cmd path in store");

    /* Tell qemu that we want it to start logging dirty page to Xen */
    strcpy(p, "cmd");
    if (!xs_write(xs, XBT_NULL, path, cmd_str, strlen(cmd_str)))
        errx(1, "can't write  to store path (%s)\n",
             path);

    /* Wait a while for qemu to signal that it has service logdirty command */
 read_again:
    tv.tv_sec = 5;
    tv.tv_usec = 0;
    FD_ZERO(&fdset);
    FD_SET(xs_fileno(xs), &fdset);

    if ((select(xs_fileno(xs) + 1, &fdset, NULL, NULL, &tv)) != 1)
        errx(1, "timed out waiting for qemu logdirty response.\n");

    watch = xs_read_watch(xs, &len);
    free(watch);

    strcpy(p, "ret");
    ret_str = xs_read(xs, XBT_NULL, path, &len);
    if (ret_str == NULL || strcmp(ret_str, cmd_str))
        /* Watch fired but value is not yet right */
        goto read_again;

    free(path);
    free(cmd_str);
    free(ret_str);

    return 0;
}

int
main(int argc, char **argv)
{
    unsigned int maxit, max_f;
    int io_fd, ret, port;
    struct save_callbacks callbacks;

    if (argc != 6)
        errx(1, "usage: %s iofd domid maxit maxf flags", argv[0]);

    si.xch = xc_interface_open(0,0,0);
    if (!si.xch)
        errx(1, "failed to open control interface");

    io_fd = atoi(argv[1]);
    si.domid = atoi(argv[2]);
    maxit = atoi(argv[3]);
    max_f = atoi(argv[4]);
    si.flags = atoi(argv[5]);

    si.suspend_evtchn = -1;

    si.xce = xc_evtchn_open(NULL, 0);
    if (si.xce == NULL)
        warnx("failed to open event channel handle");
    else
    {
        port = xs_suspend_evtchn_port(si.domid);

        if (port < 0)
            warnx("failed to get the suspend evtchn port\n");
        else
        {
            si.suspend_evtchn =
              xc_suspend_evtchn_init(si.xch, si.xce, si.domid, port);

            if (si.suspend_evtchn < 0)
                warnx("suspend event channel initialization failed, "
                       "using slow path");
        }
    }
    memset(&callbacks, 0, sizeof(callbacks));
    callbacks.suspend = suspend;
    callbacks.switch_qemu_logdirty = switch_qemu_logdirty;
    ret = xc_domain_save(si.xch, io_fd, si.domid, maxit, max_f, si.flags, 
                         &callbacks, !!(si.flags & XCFLAGS_HVM), 0);

    if (si.suspend_evtchn > 0)
	 xc_suspend_evtchn_release(si.xch, si.xce, si.domid, si.suspend_evtchn);

    if (si.xce > 0)
        xc_evtchn_close(si.xce);

    xc_interface_close(si.xch);

    return ret;
}