plugins: add [pre|post]fork helpers to linux-user

Special care needs to be taken in ensuring locks are in a consistent
state across fork events. Add helpers so the plugin system can ensure
that.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/358
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Tested-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221004115221.2174499-1-alex.bennee@linaro.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/plugins/core.c b/plugins/core.c
index c3ae284994..ccb770a485 100644
--- a/plugins/core.c
+++ b/plugins/core.c
@@ -527,6 +527,26 @@ void qemu_plugin_user_exit(void)
 }
 
 /*
+ * Helpers for *-user to ensure locks are sane across fork() events.
+ */
+
+void qemu_plugin_user_prefork_lock(void)
+{
+    qemu_rec_mutex_lock(&plugin.lock);
+}
+
+void qemu_plugin_user_postfork(bool is_child)
+{
+    if (is_child) {
+        /* should we just reset via plugin_init? */
+        qemu_rec_mutex_init(&plugin.lock);
+    } else {
+        qemu_rec_mutex_unlock(&plugin.lock);
+    }
+}
+
+
+/*
  * Call this function after longjmp'ing to the main loop. It's possible that the
  * last instruction of a TB might have used helpers, and therefore the
  * "disable" instruction will never execute because it ended up as dead code.