From: Richard W.M. Jones <rjones@redhat.com> Libguestfs wants to use qemu to run a captive appliance. When the program linked to libguestfs exits, we want qemu to be cleaned up. Libguestfs goes to great lengths to do this at the moment: it either forks a separate process to ensure clean-up is done, or it asks libvirt to clean up the qemu process. However this is complicated and not totally reliable. On Linux, FreeBSD and macOS, there are mechanisms to ensure a signal or message is delivered to a process when its parent process goes away. The qemu test suite even uses this mechanism on Linux (see PR_SET_PDEATHSIG in tests/qtest/libqtest.c). In nbdkit we have long had the concept of running nbdkit captively, and we have the nbdkit --exit-with-parent flag to help (https://libguestfs.org/nbdkit-captive.1.html#EXIT-WITH-PARENT) This commit adds the same mechanism. The syntax is: qemu -run-with exit-with-parent=on [...] This is not a feature that most typical users of qemu (for running general purpose, long-lived VMs) should use, so it defaults to off. The exit-with-parent.[ch] files are copied from nbdkit, where they have a 3-clause BSD license which is compatible with qemu: https://gitlab.com/nbdkit/nbdkit/-/tree/master/common/utils?ref_type=heads Thanks: Daniel P. Berrangé <berrange@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Signed-off-by: Richard W.M. Jones <rjones@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- include/qemu/exit-with-parent.h | 57 +++++++++++++ qemu-options.hx | 13 ++- system/exit-with-parent.c | 140 ++++++++++++++++++++++++++++++++ system/meson.build | 1 + system/vl.c | 13 +++ 5 files changed, 222 insertions(+), 2 deletions(-) create mode 100644 include/qemu/exit-with-parent.h create mode 100644 system/exit-with-parent.c diff --git a/include/qemu/exit-with-parent.h b/include/qemu/exit-with-parent.h new file mode 100644 index 0000000000..c00b863fe9 --- /dev/null +++ b/include/qemu/exit-with-parent.h @@ -0,0 +1,57 @@ +/* + * SPDX-License-Identifier: BSD-3-Clause + * Originally derived from nbdkit common/utils/exit-with-parent.h + * Copyright Red Hat + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * * Neither the name of Red Hat nor the names of its contributors may be + * used to endorse or promote products derived from this software without + * specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#ifndef NBDKIT_EXIT_WITH_PARENT_H +#define NBDKIT_EXIT_WITH_PARENT_H + +/* Test if the feature is available on the platform. */ +static inline bool can_exit_with_parent(void) +{ +#if defined(__linux__) || defined(__FreeBSD__) || defined(__APPLE__) + return true; +#else + return false; +#endif +} + +/* + * --exit-with-parent: kill the current process if the parent exits. + * This may return -1 on error. + * + * Note this will abort on platforms where can_exit_with_parent() + * returned false. + */ +extern int set_exit_with_parent(void); + +#endif /* NBDKIT_EXIT_WITH_PARENT_H */ diff --git a/qemu-options.hx b/qemu-options.hx index 0223ceffeb..fca2b7bc74 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -5467,15 +5467,18 @@ DEF("qtest-log", HAS_ARG, QEMU_OPTION_qtest_log, "", QEMU_ARCH_ALL) #if defined(CONFIG_POSIX) && !defined(EMSCRIPTEN) DEF("run-with", HAS_ARG, QEMU_OPTION_run_with, - "-run-with [async-teardown=on|off][,chroot=dir][user=username|uid:gid]\n" + "-run-with [async-teardown=on|off][,chroot=dir]\n" \ + " [,exit-with-parent=on|off][,user=username|uid:gid]\n" " Set miscellaneous QEMU process lifecycle options:\n" " async-teardown=on enables asynchronous teardown (Linux only)\n" + " exit-with-parent=on causes QEMU to exit if the parent\n" + " process of QEMU exits (Linux, FreeBSD, macOS only)\n" " chroot=dir chroot to dir just before starting the VM\n" " user=username switch to the specified user before starting the VM\n" " user=uid:gid ditto, but use specified user-ID and group-ID instead\n", QEMU_ARCH_ALL) SRST -``-run-with [async-teardown=on|off][,chroot=dir][user=username|uid:gid]`` +``-run-with [async-teardown=on|off][,chroot=dir][,exit-with-parent=on|off][,user=username|uid:gid]`` Set QEMU process lifecycle options. ``async-teardown=on`` enables asynchronous teardown. A new process called @@ -5493,6 +5496,12 @@ SRST immediately before starting the guest execution. This is especially useful in combination with ``user=...``. + ``exit-with-parent=on`` causes QEMU to exit if the parent process of + QEMU exits. This can be used when QEMU runs a captive appliance, + where the lifetime of the appliance is scoped to the parent process. + In case the parent process crashes, QEMU is still cleaned up. + This only works on Linux, FreeBSD and macOS platforms. + ``user=username`` or ``user=uid:gid`` can be used to drop root privileges before starting guest execution. QEMU will use the ``setuid`` and ``setgid`` system calls to switch to the specified identity. Note that the diff --git a/system/exit-with-parent.c b/system/exit-with-parent.c new file mode 100644 index 0000000000..df65d2231a --- /dev/null +++ b/system/exit-with-parent.c @@ -0,0 +1,140 @@ +/* + * SPDX-License-Identifier: BSD-3-Clause + * Originally derived from nbdkit common/utils/exit-with-parent.c + * Copyright Red Hat + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * * Neither the name of Red Hat nor the names of its contributors may be + * used to endorse or promote products derived from this software without + * specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +/* + * Implement the --exit-with-parent feature on operating systems which + * support it. + */ + +#include "qemu/osdep.h" +#include "qemu/exit-with-parent.h" + +#if defined(__linux__) + +#include <sys/prctl.h> + +/* + * Send SIGTERM to self when the parent exits. This will cause + * qemu_system_killed() to be called. + * + * PR_SET_PDEATHSIG has been defined since Linux 2.1.57. + */ +int +set_exit_with_parent(void) +{ + return prctl(PR_SET_PDEATHSIG, SIGTERM); +} + +#elif defined(__FreeBSD__) + +#include <sys/procctl.h> + +/* + * Send SIGTERM to self when the parent exits. This will cause + * qemu_system_killed() to be called. + * + * PROC_PDEATHSIG_CTL has been defined since FreeBSD 11.2. + */ +int +set_exit_with_parent(void) +{ + const int sig = SIGTERM; + return procctl(P_PID, 0, PROC_PDEATHSIG_CTL, (void *) &sig); +} + +#elif defined(__APPLE__) + +/* For macOS. */ + +#include "qemu/thread.h" +#include "qemu/error-report.h" +#include "system/runstate.h" +#include <sys/event.h> + +static void * +exit_with_parent_loop(void *vp) +{ + const pid_t ppid = getppid(); + int fd; + struct kevent kev, res[1]; + int r; + + /* Register the kevent to wait for ppid to exit. */ + fd = kqueue(); + if (fd == -1) { + error_report("exit_with_parent_loop: kqueue: %m"); + return NULL; + } + EV_SET(&kev, ppid, EVFILT_PROC, EV_ADD | EV_ENABLE, NOTE_EXIT, 0, NULL); + if (kevent(fd, &kev, 1, NULL, 0, NULL) == -1) { + error_report("exit_with_parent_loop: kevent: %m"); + close(fd); + return NULL; + } + + /* Wait for the kevent to happen. */ + r = kevent(fd, 0, 0, res, 1, NULL); + if (r == 1 && res[0].ident == ppid) { + /* Behave like Linux and FreeBSD above, as if SIGTERM was sent */ + qemu_system_killed(SIGTERM, ppid); + } + + return NULL; +} + +int +set_exit_with_parent(void) +{ + QemuThread exit_with_parent_thread; + + /* + * We have to block waiting for kevent, so that requires that we + * start a background thread. + */ + qemu_thread_create(&exit_with_parent_thread, + "exit-parent", + exit_with_parent_loop, NULL, + QEMU_THREAD_DETACHED); + return 0; +} + +#else /* any platform that doesn't support this function */ + +int +set_exit_with_parent(void) +{ + g_assert_not_reached(); +} + +#endif diff --git a/system/meson.build b/system/meson.build index 6d21ff9faa..4b69ef0f5f 100644 --- a/system/meson.build +++ b/system/meson.build @@ -15,6 +15,7 @@ system_ss.add(files( 'datadir.c', 'dirtylimit.c', 'dma-helpers.c', + 'exit-with-parent.c', 'globals.c', 'ioport.c', 'ram-block-attributes.c', diff --git a/system/vl.c b/system/vl.c index 29f5389151..5091fe52d9 100644 --- a/system/vl.c +++ b/system/vl.c @@ -53,6 +53,7 @@ #include "qemu/sockets.h" #include "qemu/accel.h" #include "qemu/async-teardown.h" +#include "qemu/exit-with-parent.h" #include "hw/usb.h" #include "hw/isa/isa.h" #include "hw/scsi/scsi.h" @@ -783,6 +784,10 @@ static QemuOptsList qemu_run_with_opts = { .name = "chroot", .type = QEMU_OPT_STRING, }, + { + .name = "exit-with-parent", + .type = QEMU_OPT_BOOL, + }, { .name = "user", .type = QEMU_OPT_STRING, @@ -3691,6 +3696,14 @@ void qemu_init(int argc, char **argv) if (str) { os_set_chroot(str); } + if (qemu_opt_get_bool(opts, "exit-with-parent", false)) { + if (!can_exit_with_parent()) { + error_report("exit-with-parent is not available" + " on this platform"); + exit(1); + } + set_exit_with_parent(); + } str = qemu_opt_get(opts, "user"); if (str) { if (!os_set_runas(str)) { -- 2.51.1