[Xen-devel] [RFC XEN PATCH for-4.13 2/4] libxl: Introduce libxl__ev_qmplock

[Anthony PERARD <anthony.perard@citrix.com>]

This lock will be used to prevent concurrent access the QEMU's QMP
socket. It is based on libxl__ev_devlock implementation and have the
same properties.

There is one addition to the ev_devlock API,
libxl__ev_qmplock_dispose, which allow to cancel the lock operation
while it is in Active state.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 tools/libxl/libxl_internal.c | 31 ++++++++++++++++++++++++++++++-
 tools/libxl/libxl_internal.h | 14 ++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index 0750b69cba61..afbb01c5722f 100644
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -583,17 +583,25 @@ void libxl__ev_devlock_init(libxl__ev_devlock *lock)
     lock->held = false;
 }
 
+static void ev_lock_lock(libxl__egc *egc, libxl__ev_devlock *lock,
+                         const char *userdata_userid);
 static void ev_lock_prepare_fork(libxl__egc *egc, libxl__ev_devlock *lock);
 static void ev_lock_child_callback(libxl__egc *egc, libxl__ev_child *child,
                                    pid_t pid, int status);
 
 void libxl__ev_devlock_lock(libxl__egc *egc, libxl__ev_devlock *lock)
+{
+    ev_lock_lock(egc, lock, "libxl-device-changes-lock");
+}
+
+static void ev_lock_lock(libxl__egc *egc, libxl__ev_devlock *lock,
+                         const char *userdata_userid)
 {
     STATE_AO_GC(lock->ao);
     const char *lockfile;
 
     lockfile = libxl__userdata_path(gc, lock->domid,
-                                    "libxl-device-changes-lock", "l");
+                                    userdata_userid, "l");
     if (!lockfile) goto out;
     lock->path = libxl__strdup(NOGC, lockfile);
 
@@ -757,6 +765,27 @@ void libxl__ev_devlock_unlock(libxl__gc *gc, libxl__ev_devlock *lock)
     libxl__ev_devlock_init(lock);
 }
 
+void libxl__ev_qmplock_init(libxl__ev_qmplock *lock)
+{
+    libxl__ev_devlock_init(lock);
+}
+
+void libxl__ev_qmplock_lock(libxl__egc *egc, libxl__ev_qmplock *lock)
+{
+    ev_lock_lock(egc, lock, "qmp-socket-lock");
+}
+
+void libxl__ev_qmplock_unlock(libxl__gc *gc, libxl__ev_qmplock *lock)
+{
+    libxl__ev_devlock_unlock(gc, lock);
+}
+
+void libxl__ev_qmplock_dispose(libxl__gc *gc, libxl__ev_qmplock *lock)
+{
+    libxl__ev_child_kill(lock->ao, &lock->child);
+    libxl__ev_devlock_unlock(gc, lock);
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 5823890703ad..115c79d034d4 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -197,6 +197,7 @@ typedef struct libxl__device_type libxl__device_type;
 typedef struct libxl__json_object libxl__json_object;
 typedef struct libxl__carefd libxl__carefd;
 typedef struct libxl__ev_devlock libxl__ev_devlock;
+typedef struct libxl__ev_devlock libxl__ev_qmplock;
 typedef struct libxl__dm_resume_state libxl__dm_resume_state;
 typedef struct libxl__ao_device libxl__ao_device;
 typedef struct libxl__multidev libxl__multidev;
@@ -4725,6 +4726,19 @@ _hidden void libxl__ev_devlock_init(libxl__ev_devlock *);
 _hidden void libxl__ev_devlock_lock(libxl__egc *, libxl__ev_devlock *);
 _hidden void libxl__ev_devlock_unlock(libxl__gc *, libxl__ev_devlock *);
 
+/* libxl__ev_qmplock
+ *
+ * See "Lock for device hotplug, qmp_lock." as it is similar but is used
+ * to regulate access the QEMU's QMP socket.
+ *
+ * libxl__ev_qmplock_dispose: Idle/Active/LockAcquired -> Idle
+ *   The callback will not be called anymore.
+ */
+_hidden void libxl__ev_qmplock_init(libxl__ev_qmplock *);
+_hidden void libxl__ev_qmplock_lock(libxl__egc *, libxl__ev_qmplock *);
+_hidden void libxl__ev_qmplock_unlock(libxl__gc *, libxl__ev_qmplock *);
+_hidden void libxl__ev_qmplock_dispose(libxl__gc *, libxl__ev_qmplock *);
+
 /* Send control commands over xenstore and wait for an Ack. */
 _hidden int libxl__domain_pvcontrol(libxl__egc *egc,
                                     libxl__xswait_state *pvcontrol,
-- 
Anthony PERARD

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