os-posix: Allow 'chroot' via '-run-with' and deprecate the old '-chroot' option

We recently introduced "-run-with" for options that influence the
runtime behavior of QEMU. This option has the big advantage that it
can group related options (so that it is easier for the users to spot
them) and that the options become introspectable via QMP this way.
So let's start moving more switches into this option group, starting
with "-chroot" now.

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Message-Id: <20230703074447.17044-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

docs/about/deprecated.rst

@@ -116,6 +116,11 @@ Use "whpx" (on Windows) or "hvf" (on macOS) instead.
 
 Use ``-run-with async-teardown=on`` instead.
 
+``-chroot`` (since 8.1)
+'''''''''''''''''''''''
+
+Use ``-run-with chroot=dir`` instead.
+
 ``-singlestep`` (since 8.1)
 '''''''''''''''''''''''''''
 

os-posix.c

@@ -38,6 +38,7 @@
 #include "qemu/cutils.h"
 #include "qemu/config-file.h"
 #include "qemu/option.h"
+#include "qemu/module.h"
 
 #ifdef CONFIG_LINUX
 #include <sys/prctl.h>
@@ -148,6 +149,7 @@ int os_parse_cmd_args(int index, const char *optarg)
         }
         break;
     case QEMU_OPTION_chroot:
+        warn_report("option is deprecated, use '-run-with chroot=...' instead");
         chroot_dir = optarg;
         break;
     case QEMU_OPTION_daemonize:
@@ -158,18 +160,25 @@ int os_parse_cmd_args(int index, const char *optarg)
     case QEMU_OPTION_asyncteardown:
         init_async_teardown();
         break;
+#endif
     case QEMU_OPTION_run_with: {
+        const char *str;
         QemuOpts *opts = qemu_opts_parse_noisily(qemu_find_opts("run-with"),
                                                  optarg, false);
         if (!opts) {
             exit(1);
         }
+#if defined(CONFIG_LINUX)
         if (qemu_opt_get_bool(opts, "async-teardown", false)) {
             init_async_teardown();
         }
+#endif
+        str = qemu_opt_get(opts, "chroot");
+        if (str) {
+            chroot_dir = str;
+        }
         break;
     }
-#endif
     default:
         return -1;
     }
@@ -348,3 +357,27 @@ int os_mlock(void)
     return -ENOSYS;
 #endif
 }
+
+static QemuOptsList qemu_run_with_opts = {
+    .name = "run-with",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_run_with_opts.head),
+    .desc = {
+#if defined(CONFIG_LINUX)
+        {
+            .name = "async-teardown",
+            .type = QEMU_OPT_BOOL,
+        },
+#endif
+        {
+            .name = "chroot",
+            .type = QEMU_OPT_STRING,
+        },
+        { /* end of list */ }
+    },
+};
+
+static void register_runwith(void)
+{
+    qemu_add_opts(&qemu_run_with_opts);
+}
+opts_init(register_runwith);

qemu-options.hx

@@ -4677,11 +4677,12 @@ ERST
 
 #ifndef _WIN32
 DEF("chroot", HAS_ARG, QEMU_OPTION_chroot, \
-    "-chroot dir     chroot to dir just before starting the VM\n",
+    "-chroot dir     chroot to dir just before starting the VM (deprecated)\n",
     QEMU_ARCH_ALL)
 #endif
 SRST
 ``-chroot dir``
+    Deprecated, use '-run-with chroot=...' instead.
     Immediately before starting guest execution, chroot to the specified
     directory. Especially useful in combination with -runas.
 ERST
@@ -4868,13 +4869,16 @@ SRST
     This option is deprecated and should no longer be used. The new option
     ``-run-with async-teardown=on`` is a replacement.
 ERST
+#endif
+#ifdef CONFIG_POSIX
 DEF("run-with", HAS_ARG, QEMU_OPTION_run_with,
-    "-run-with async-teardown[=on|off]\n"
-    "                misc QEMU process lifecycle options\n"
-    "                async-teardown=on enables asynchronous teardown\n",
+    "-run-with [async-teardown=on|off][,chroot=dir]\n"
+    "                Set miscellaneous QEMU process lifecycle options:\n"
+    "                async-teardown=on enables asynchronous teardown (Linux only)\n"
+    "                chroot=dir chroot to dir just before starting the VM\n",
     QEMU_ARCH_ALL)
 SRST
-``-run-with``
+``-run-with [async-teardown=on|off][,chroot=dir]``
     Set QEMU process lifecycle options.
 
     ``async-teardown=on`` enables asynchronous teardown. A new process called
@@ -4887,6 +4891,10 @@ SRST
     performed correctly. This only works if the cleanup process is not
     forcefully killed with SIGKILL before the main QEMU process has
     terminated completely.
+
+    ``chroot=dir`` can be used for doing a chroot to the specified directory
+    immediately before starting the guest execution. This is especially useful
+    in combination with -runas.
 ERST
 #endif
 

util/async-teardown.c

@@ -12,9 +12,6 @@
  */
 
 #include "qemu/osdep.h"
-#include "qemu/config-file.h"
-#include "qemu/option.h"
-#include "qemu/module.h"
 #include <dirent.h>
 #include <sys/prctl.h>
 #include <sched.h>
@@ -147,21 +144,3 @@ void init_async_teardown(void)
     clone(async_teardown_fn, new_stack_for_clone(), CLONE_VM, NULL);
     sigprocmask(SIG_SETMASK, &old_signals, NULL);
 }
-
-static QemuOptsList qemu_run_with_opts = {
-    .name = "run-with",
-    .head = QTAILQ_HEAD_INITIALIZER(qemu_run_with_opts.head),
-    .desc = {
-        {
-            .name = "async-teardown",
-            .type = QEMU_OPT_BOOL,
-        },
-        { /* end of list */ }
-    },
-};
-
-static void register_teardown(void)
-{
-    qemu_add_opts(&qemu_run_with_opts);
-}
-opts_init(register_teardown);