[RFC,4/5] plugins: add time control API

Commit Message

Pierrick Bouvier March 13, 2024, 10:55 a.m. UTC

From: Alex Bennée <[e-mail]>

Expose the ability to control time through the plugin API. Only one
plugin can control time so it has to request control when loaded.
There are probably more corner cases to catch here.

Signed-off-by: Alex Bennée <[e-mail]>
---
 include/qemu/qemu-plugin.h   | 23 +++++++++++++++++++++++
 plugins/api.c                | 31 +++++++++++++++++++++++++++++++
 plugins/qemu-plugins.symbols |  2 ++
 3 files changed, 56 insertions(+)

Patch

diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
index 337de25ece7..f2a0253e594 100644
--- a/include/qemu/qemu-plugin.h
+++ b/include/qemu/qemu-plugin.h
@@ -662,6 +662,29 @@  void qemu_plugin_register_vcpu_mem_inline_per_vcpu(
     qemu_plugin_u64 entry,
     uint64_t imm);
 
+/**
+ * qemu_plugin_request_time_control() - request the ability to control time
+ *
+ * This grants the plugin the ability to control system time. Only one
+ * plugin can control time so if multiple plugins request the ability
+ * all but the first will fail.
+ *
+ * Returns an opaque handle or NULL if fails
+ */
+const void *qemu_plugin_request_time_control(void);
+
+/**
+ * qemu_plugin_update_ns() - update system emulation time
+ * @handle: opaque handle returned by qemu_plugin_request_time_control()
+ * @time: time in nanoseconds
+ *
+ * This allows an appropriately authorised plugin (i.e. holding the
+ * time control handle) to move system time forward to @time.
+ *
+ * Start time is 0.
+ */
+void qemu_plugin_update_ns(const void *handle, int64_t time);
+
 typedef void
 (*qemu_plugin_vcpu_syscall_cb_t)(qemu_plugin_id_t id, unsigned int vcpu_index,
                                  int64_t num, uint64_t a1, uint64_t a2,
diff --git a/plugins/api.c b/plugins/api.c
index fdf6167655e..f8b2d09ad0c 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -39,6 +39,7 @@ 
 #include "qemu/main-loop.h"
 #include "qemu/plugin.h"
 #include "qemu/log.h"
+#include "qemu/timer.h"
 #include "tcg/tcg.h"
 #include "exec/exec-all.h"
 #include "exec/gdbstub.h"
@@ -591,3 +592,33 @@  uint64_t qemu_plugin_u64_sum(qemu_plugin_u64 entry)
     }
     return total;
 }
+
+/*
+ * Time control
+ */
+static bool has_control;
+
+const void *qemu_plugin_request_time_control(void)
+{
+    if (!has_control) {
+        has_control = true;
+        return &has_control;
+    }
+    return NULL;
+}
+
+static void advance_virtual_time__async(CPUState *cpu, run_on_cpu_data data)
+{
+    int64_t new_time = data.host_ulong;
+    qemu_clock_advance_virtual_time(new_time);
+}
+
+void qemu_plugin_update_ns(const void *handle, int64_t new_time)
+{
+    if (handle == &has_control) {
+        /* Need to execute out of cpu_exec, so bql can be locked. */
+        async_run_on_cpu(current_cpu,
+                         advance_virtual_time__async,
+                         RUN_ON_CPU_HOST_ULONG(new_time));
+    }
+}
diff --git a/plugins/qemu-plugins.symbols b/plugins/qemu-plugins.symbols
index aa0a77a319f..ca773d8d9fe 100644
--- a/plugins/qemu-plugins.symbols
+++ b/plugins/qemu-plugins.symbols
@@ -38,6 +38,7 @@ 
   qemu_plugin_register_vcpu_tb_exec_cond_cb;
   qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu;
   qemu_plugin_register_vcpu_tb_trans_cb;
+  qemu_plugin_request_time_control;
   qemu_plugin_reset;
   qemu_plugin_scoreboard_free;
   qemu_plugin_scoreboard_find;
@@ -51,5 +52,6 @@ 
   qemu_plugin_u64_set;
   qemu_plugin_u64_sum;
   qemu_plugin_uninstall;
+  qemu_plugin_update_ns;
   qemu_plugin_vcpu_for_each;
 };