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Re: [Qemu-block] [PATCH 1/4] lockable: add QemuLockable


From: Fam Zheng
Subject: Re: [Qemu-block] [PATCH 1/4] lockable: add QemuLockable
Date: Tue, 16 Jan 2018 11:01:48 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0



On 01/16/2018 06:08 AM, Paolo Bonzini wrote:
QemuLockable is a polymorphic lock type that takes an object and
knows which function to use for locking and unlocking.  The
implementation could use C11 _Generic, but since the support is
not very widespread I am instead using __builtin_choose_expr and
__builtin_types_compatible_p, which are already used by
include/qemu/atomic.h.

QemuLockable can be used to implement lock guards, or to pass around
a lock in such a way that a function can release it and re-acquire it.
The next patch will do this for CoQueue.

Signed-off-by: Paolo Bonzini <address@hidden>
---
  include/qemu/compiler.h  | 40 ++++++++++++++++++++++++++
  include/qemu/coroutine.h |  4 +--
  include/qemu/lockable.h  | 75 ++++++++++++++++++++++++++++++++++++++++++++++++
  include/qemu/thread.h    |  5 ++--
  include/qemu/typedefs.h  |  4 +++
  5 files changed, 123 insertions(+), 5 deletions(-)
  create mode 100644 include/qemu/lockable.h

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 340e5fdc09..5179bedb1e 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -111,4 +111,44 @@
  #define GCC_FMT_ATTR(n, m)
  #endif
+/* Implement C11 _Generic via GCC builtins. Example:
+ *
+ *    QEMU_GENERIC(x, (float, sinf), (long double, sinl), sin) (x)
+ *
+ * The first argument is the discriminator.  The last is the default value.
+ * The middle ones are tuples in "(type, expansion)" format.
+ */
+
+/* First, find out the number of generic cases.  */
+#define QEMU_GENERIC(x, ...) \
+    QEMU_GENERIC_(typeof(x), __VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+
+/* There will be extra arguments, but they are not used.  */
+#define QEMU_GENERIC_(x, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, count, ...) \
+    QEMU_GENERIC##count(x, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9)
+
+/* Two more helper macros, this time to extract items from a parenthesized
+ * list.
+ */
+#define QEMU_FIRST_(a, b) a
+#define QEMU_SECOND_(a, b) b
+
+/* ... and a final one for the common part of the "recursion".  */
+#define QEMU_GENERIC_IF_(x, type_then, else_)                                  
\
+    __builtin_choose_expr(__builtin_types_compatible_p(x,                      
\
+                                                       QEMU_FIRST_ type_then), 
\
+                          QEMU_SECOND_ type_then, else_)
+
+/* CPP poor man's "recursion".  */
+#define QEMU_GENERIC1(x, a0, ...) (a0)
+#define QEMU_GENERIC2(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC1(x, 
__VA_ARGS__))
+#define QEMU_GENERIC3(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC2(x, 
__VA_ARGS__))
+#define QEMU_GENERIC4(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC3(x, 
__VA_ARGS__))
+#define QEMU_GENERIC5(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC4(x, 
__VA_ARGS__))
+#define QEMU_GENERIC6(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC5(x, 
__VA_ARGS__))
+#define QEMU_GENERIC7(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC6(x, 
__VA_ARGS__))
+#define QEMU_GENERIC8(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC7(x, 
__VA_ARGS__))
+#define QEMU_GENERIC9(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC8(x, 
__VA_ARGS__))
+#define QEMU_GENERIC10(x, a0, ...) QEMU_GENERIC_IF_(x, a0, QEMU_GENERIC9(x, 
__VA_ARGS__))
+
  #endif /* COMPILER_H */
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index ce2eb73670..8a5129741c 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -121,7 +121,7 @@ bool qemu_coroutine_entered(Coroutine *co);
   * Provides a mutex that can be used to synchronise coroutines
   */
  struct CoWaitRecord;
-typedef struct CoMutex {
+struct CoMutex {
      /* Count of pending lockers; 0 for a free mutex, 1 for an
       * uncontended mutex.
       */
@@ -142,7 +142,7 @@ typedef struct CoMutex {
      unsigned handoff, sequence;
Coroutine *holder;
-} CoMutex;
+};
/**
   * Initialises a CoMutex. This must be called before any other operation is 
used
diff --git a/include/qemu/lockable.h b/include/qemu/lockable.h
new file mode 100644
index 0000000000..e280431290
--- /dev/null
+++ b/include/qemu/lockable.h
@@ -0,0 +1,75 @@
+/*
+ * Polymorphic locking functions (like templates, but in C)
+ *
+ * Copyright Red Hat, Inc. 2017
2017 - 2018?
+ *
+ * Author: Paolo Bonzini <address@hidden>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_LOCKABLE_H
+#define QEMU_LOCKABLE_H
+
+#include "qemu/coroutine.h"
+#include "qemu/thread.h"
+
+typedef void QemuLockUnlockFunc(void *);
+
+struct QemuLockable {
+    void *object;
+    QemuLockUnlockFunc *lock;
+    QemuLockUnlockFunc *unlock;
+};
+
+/* This function is used to give link-time errors if an invalid, non-NULL
+ * pointer type is passed to QEMU_MAKE_LOCKABLE.
+ */
+void unknown_lock_type(void *);
+
+/* Auxiliary macros to simplify QEMU_MAKE_LOCABLE.  */
*LOCKABLE*

Fam
+#define QEMU_LOCK_FUNC(x) ((QemuLockUnlockFunc *)    \
+    QEMU_GENERIC(x,                                  \
+                 (QemuMutex *, qemu_mutex_lock),     \
+                 (CoMutex *, qemu_co_mutex_lock),    \
+                 (QemuSpin *, qemu_spin_lock),       \
+                 ((x) ? unknown_lock_type : NULL)))
+
+#define QEMU_UNLOCK_FUNC(x) ((QemuLockUnlockFunc *)  \
+    QEMU_GENERIC(x,                                  \
+                 (QemuMutex *, qemu_mutex_unlock),   \
+                 (CoMutex *, qemu_co_mutex_unlock),  \
+                 (QemuSpin *, qemu_spin_unlock),     \
+                 ((x) ? unknown_lock_type : NULL)))
+
+#define QEMU_MAKE_LOCKABLE_(x) (&(QemuLockable) {    \
+        .object = (x),                               \
+        .lock = QEMU_LOCK_FUNC(x),                   \
+        .unlock = QEMU_UNLOCK_FUNC(x),               \
+    })
+
+/* QEMU_MAKE_LOCKABLE - Make a polymorphic QemuLockable
+ *
+ * @x: a lock object (currently one of QemuMutex, CoMutex, QemuSpin).
+ *
+ * Returns a QemuLockable object that can be passed around
+ * to a function that can operate with locks of any kind.
+ */
+#define QEMU_MAKE_LOCKABLE(x)                        \
+    QEMU_GENERIC(x,                                  \
+                 (QemuLockable *, x),                \
+                 QEMU_MAKE_LOCKABLE_(x))
+
+static inline void qemu_lockable_lock(QemuLockable *x)
+{
+    x->lock(x);
+}
+
+static inline void qemu_lockable_unlock(QemuLockable *x)
+{
+    x->unlock(x);
+}
+
+#endif
diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index 9910f49b3a..a3bc056d89 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -4,7 +4,6 @@
  #include "qemu/processor.h"
  #include "qemu/atomic.h"
-typedef struct QemuMutex QemuMutex;
  typedef struct QemuCond QemuCond;
  typedef struct QemuSemaphore QemuSemaphore;
  typedef struct QemuEvent QemuEvent;
@@ -66,9 +65,9 @@ struct Notifier;
  void qemu_thread_atexit_add(struct Notifier *notifier);
  void qemu_thread_atexit_remove(struct Notifier *notifier);
-typedef struct QemuSpin {
+struct QemuSpin {
      int value;
-} QemuSpin;
+};
static inline void qemu_spin_init(QemuSpin *spin)
  {
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 9bd7a834ba..5923849cdd 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -19,6 +19,7 @@ typedef struct BusClass BusClass;
  typedef struct BusState BusState;
  typedef struct Chardev Chardev;
  typedef struct CompatProperty CompatProperty;
+typedef struct CoMutex CoMutex;
  typedef struct CPUAddressSpace CPUAddressSpace;
  typedef struct CPUState CPUState;
  typedef struct DeviceListener DeviceListener;
@@ -86,9 +87,12 @@ typedef struct QEMUBH QEMUBH;
  typedef struct QemuConsole QemuConsole;
  typedef struct QemuDmaBuf QemuDmaBuf;
  typedef struct QEMUFile QEMUFile;
+typedef struct QemuLockable QemuLockable;
+typedef struct QemuMutex QemuMutex;
  typedef struct QemuOpt QemuOpt;
  typedef struct QemuOpts QemuOpts;
  typedef struct QemuOptsList QemuOptsList;
+typedef struct QemuSpin QemuSpin;
  typedef struct QEMUSGList QEMUSGList;
  typedef struct QEMUTimer QEMUTimer;
  typedef struct QEMUTimerListGroup QEMUTimerListGroup;




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