system: introduce a new MlockState enum

Replace the boolean value enable_mlock with an enum and add a helper to
decide whether we should be calling os_mlock.

This is a stepping stone towards introducing a new mlock mode, which
will be the third possible state of this enum.

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Link: https://lore.kernel.org/r/20250212143920.1269754-4-d-tatianin@yandex-team.ru
Signed-off-by: Peter Xu <peterx@redhat.com>

5 files changed, 24 insertions, 6 deletions

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index b1a0037..7b140ad 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -991,7 +991,7 @@ static void virtio_mem_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    if (enable_mlock) {
+    if (should_mlock(mlock_state)) {
         error_setg(errp, "Incompatible with mlock");
         return;
     }
diff --git a/include/system/system.h b/include/system/system.h
index 0cbb43e..dc76283 100644
--- a/include/system/system.h
+++ b/include/system/system.h
@@ -44,10 +44,18 @@ extern int display_opengl;
 extern const char *keyboard_layout;
 extern int old_param;
 extern uint8_t *boot_splash_filedata;
-extern bool enable_mlock;
 extern bool enable_cpu_pm;
 extern QEMUClockType rtc_clock;
 
+typedef enum {
+    MLOCK_OFF = 0,
+    MLOCK_ON,
+} MlockState;
+
+bool should_mlock(MlockState);
+
+extern MlockState mlock_state;
+
 #define MAX_OPTION_ROMS 16
 typedef struct QEMUOptionRom {
     const char *name;
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index fc4d8a1..04068ee 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -651,7 +651,7 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
         mis->have_fault_thread = false;
     }
 
-    if (enable_mlock) {
+    if (should_mlock(mlock_state)) {
         if (os_mlock(false) < 0) {
             error_report("mlock: %s", strerror(errno));
             /*
diff --git a/system/globals.c b/system/globals.c
index 4867c93..adeff38 100644
--- a/system/globals.c
+++ b/system/globals.c
@@ -31,10 +31,15 @@
 #include "system/cpus.h"
 #include "system/system.h"
 
+bool should_mlock(MlockState state)
+{
+    return state == MLOCK_ON;
+}
+
 enum vga_retrace_method vga_retrace_method = VGA_RETRACE_DUMB;
 int display_opengl;
 const char* keyboard_layout;
-bool enable_mlock;
+MlockState mlock_state;
 bool enable_cpu_pm;
 int autostart = 1;
 int vga_interface_type = VGA_NONE;
diff --git a/system/vl.c b/system/vl.c
index 72a4098..2895824 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -796,7 +796,7 @@ static QemuOptsList qemu_run_with_opts = {
 
 static void realtime_init(void)
 {
-    if (enable_mlock) {
+    if (should_mlock(mlock_state)) {
         if (os_mlock(false) < 0) {
             error_report("locking memory failed");
             exit(1);
@@ -1878,13 +1878,18 @@ static void object_option_parse(const char *str)
 static void overcommit_parse(const char *str)
 {
     QemuOpts *opts;
+    bool enable_mlock;
 
     opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"),
                                    str, false);
     if (!opts) {
         exit(1);
     }
-    enable_mlock = qemu_opt_get_bool(opts, "mem-lock", enable_mlock);
+
+    enable_mlock = qemu_opt_get_bool(opts, "mem-lock",
+                                     should_mlock(mlock_state));
+    mlock_state = enable_mlock ? MLOCK_ON : MLOCK_OFF;
+
     enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", enable_cpu_pm);
 }