[PATCH v2 0/2] Implement -run-with exit-with-parent=on

[PATCH v2 0/2] Implement -run-with exit-with-parent=on

[Richard W.M. Jones]

v1 was here:

https://lists.gnu.org/archive/html/qemu-devel/2025-10/msg00762.html

In v2:

 - Fix unused variable warning.

 - Remove the #ifdefs from the libqtest.c code.

 - Add the missing S-o-B in the second patch.

 - Rebase and retest.

As before, one test fails both before and after this change:

  4/405 qemu:func-quick+func-x86_64 / func-x86_64-bad_vmstate               ERROR            0.15s   exit status 1

And as before, some questions:

 - There's no way to find out if the qemu binary supports
   exit-with-parent=on except to try it.  Maybe this should be exposed
   somehow?

 - Or should we have exit-with-parent=best ?

 - On macOS I wasn't able to find a satisfactory way to force
   shutdown, except calling 'qemu_system_killed' and pretending we'd
   been killed by SIGTERM (which does at least emulate what Linux &
   FreeBSD do).  I suppose it'd be nice if there was a "killed by
   parent" reason which also forced shutdown.

Rich.

[PATCH v2 1/2] Implement -run-with exit-with-parent=on

[Richard W.M. Jones]

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>
Signed-off-by: Richard W.M. Jones <rjones@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(-)

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 cc2ef4424e..bf745f354d 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 646239e4a6..1fbd37328c 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,
@@ -3690,6 +3695,14 @@ 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)) {
-- 
2.50.1

Re: [PATCH v2 1/2] Implement -run-with exit-with-parent=on

[Daniel P. Berrangé]

On Thu, Oct 09, 2025 at 05:12:46PM +0100, Richard W.M. Jones wrote:
> 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>
> Signed-off-by: Richard W.M. Jones <rjones@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(-)
> 
> 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 @@

snip

> +
> +#ifndef NBDKIT_EXIT_WITH_PARENT_H
> +#define NBDKIT_EXIT_WITH_PARENT_H

I'd suggest s/NBDKIT/QEMU/ here & at the end

> +
> +/* 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 */



With that minor change

 Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
 

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Re: [PATCH v2 1/2] Implement -run-with exit-with-parent=on

[Thomas Huth]

On 09/10/2025 18.12, Richard W.M. Jones wrote:
> 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>
> Signed-off-by: Richard W.M. Jones <rjones@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(-)
> 
> 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 cc2ef4424e..bf745f354d 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);

So in case of errors, fd is closed here ...

> +        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;
> +}
... but if everything goes well, fd does not get closed? Should there be a 
close(fd) after the kevent() here?

  Thomas

Re: [PATCH v2 1/2] Implement -run-with exit-with-parent=on

[Richard W.M. Jones]

On Mon, May 18, 2026 at 06:49:11PM +0200, Thomas Huth wrote:
> On 09/10/2025 18.12, Richard W.M. Jones wrote:
> >+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);
> 
> So in case of errors, fd is closed here ...
> 
> >+        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;
> >+}
> ... but if everything goes well, fd does not get closed? Should
> there be a close(fd) after the kevent() here?

Yes .. although of course qemu as a whole will exit very soon
afterwards :-)

Do you want me to submit a patch or will you do it?

I'll fix the equivalent code in nbdkit.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
nbdkit - Flexible, fast NBD server with plugins
https://gitlab.com/nbdkit/nbdkit

Re: [PATCH v2 1/2] Implement -run-with exit-with-parent=on

[Thomas Huth]

On 18/05/2026 18.54, Richard W.M. Jones wrote:
> On Mon, May 18, 2026 at 06:49:11PM +0200, Thomas Huth wrote:
>> On 09/10/2025 18.12, Richard W.M. Jones wrote:
>>> +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);
>>
>> So in case of errors, fd is closed here ...
>>
>>> +        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;
>>> +}
>> ... but if everything goes well, fd does not get closed? Should
>> there be a close(fd) after the kevent() here?
> 
> Yes .. although of course qemu as a whole will exit very soon
> afterwards :-)
> 
> Do you want me to submit a patch or will you do it?

If you've got some spare minutes, I'd appreciate if you could send a patch.

  Thanks,
   Thomas

Re: [PATCH v2 1/2] Implement -run-with exit-with-parent=on

[Richard W.M. Jones]

This is the nbdkit fix:
https://gitlab.com/nbdkit/nbdkit/-/commit/16a860c805c17eb784f33a218b7e19cd99cd9c7a

I tested it on macOS & it appears to work fine.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top

[PATCH v2 2/2] tests/qtest: Use exit-with-parent=on in qtest invocations

[Richard W.M. Jones]

Previously libqtest.c set PR_SET_PDEATHSIG (or the equivalent on
FreeBSD) after forking the qemu subprocess.  However we can get the
same behaviour now by using the new -run-with exit-with-parent=on
flag, on platforms that support it.

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 tests/qtest/libqtest.c | 22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/tests/qtest/libqtest.c b/tests/qtest/libqtest.c
index 933d085869..622464e365 100644
--- a/tests/qtest/libqtest.c
+++ b/tests/qtest/libqtest.c
@@ -33,6 +33,7 @@
 #include "qemu/accel.h"
 #include "qemu/ctype.h"
 #include "qemu/cutils.h"
+#include "qemu/exit-with-parent.h"
 #include "qemu/sockets.h"
 #include "qobject/qdict.h"
 #include "qobject/qjson.h"
@@ -433,24 +434,6 @@ static QTestState *qtest_spawn_qemu(const char *qemu_bin, const char *args,
 #ifndef _WIN32
     pid = fork();
     if (pid == 0) {
-#ifdef __linux__
-        /*
-         * Although we register a ABRT handler to kill off QEMU
-         * when g_assert() triggers, we want an extra safety
-         * net. The QEMU process might be non-functional and
-         * thus not have responded to SIGTERM. The test script
-         * might also have crashed with SEGV, in which case the
-         * cleanup handlers won't ever run.
-         *
-         * This PR_SET_PDEATHSIG setup will ensure any remaining
-         * QEMU will get terminated with SIGKILL in these cases.
-         */
-        prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
-#endif /* __linux__ */
-#ifdef __FreeBSD__
-        int sig = SIGKILL;
-        procctl(P_PID, getpid(), PROC_PDEATHSIG_CTL, &sig);
-#endif /* __FreeBSD__ */
         execlp("/bin/sh", "sh", "-c", command->str, NULL);
         exit(1);
     }
@@ -482,12 +465,15 @@ gchar *qtest_qemu_args(const char *extra_args)
                       "-display none "
                       "-audio none "
                       "%s"
+                      "%s"
                       " -accel qtest",
 
                       tracearg,
                       socket_path,
                       getenv("QTEST_LOG") ? DEV_STDERR : DEV_NULL,
                       qmp_socket_path,
+                      can_exit_with_parent() ?
+                      "-run-with exit-with-parent=on " : "",
                       extra_args ?: "");
 
     return args;
-- 
2.50.1

Re: [PATCH v2 2/2] tests/qtest: Use exit-with-parent=on in qtest invocations

[Daniel P. Berrangé]

On Thu, Oct 09, 2025 at 05:12:47PM +0100, Richard W.M. Jones wrote:
> Previously libqtest.c set PR_SET_PDEATHSIG (or the equivalent on
> FreeBSD) after forking the qemu subprocess.  However we can get the
> same behaviour now by using the new -run-with exit-with-parent=on
> flag, on platforms that support it.

Perhaps note

  "This conversion extends the qtest auto-cleanup to macOS"

> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  tests/qtest/libqtest.c | 22 ++++------------------
>  1 file changed, 4 insertions(+), 18 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|