[Minios-devel] [UNIKRAFT PATCH v2] include/refcount: A reference counter support

[Sharan Santhanam <sharan.santhanam@xxxxxxxxx>]

This patch provides support to track the number of reference held
to an object. The reference counter implementation provides
support for:

* uk_refcount_init - Initialize the counter
* uk_refcount_acquire - Atomically increment the counter
* uk_refcount_release - Release the reference
* uk_refcount_acquire_if_not_zero - Atomically acquire the counter
                                                                        if 
greater than zero.
* uk_refcount_release_if_not_last - Atomically release the reference
                                                                        if it 
is not last. The last release
                                                                        should 
free up the necessary memory
                                                                        tracked.

Changes since v1:
* The refcount data structure is independent of the UKDEBUG library which
  provides UK_ASSERT.
* Asserting for overflow, in the uk_refcount_acquire_if_not_zero.

Taken from Freebsd commit-id: 81c19620beed0e

Signed-off-by: Sharan Santhanam <sharan.santhanam@xxxxxxxxx>
---
 include/uk/arch/atomic.h |  19 +++++
 include/uk/arch/types.h  |   4 ++
 include/uk/refcount.h    | 183 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 206 insertions(+)
 create mode 100644 include/uk/refcount.h

diff --git a/include/uk/arch/atomic.h b/include/uk/arch/atomic.h
index 558067d..5fec756 100644
--- a/include/uk/arch/atomic.h
+++ b/include/uk/arch/atomic.h
@@ -54,6 +54,25 @@ extern "C" {
  */
 #define ukarch_load_n(src) \
        __atomic_load_n(src, __ATOMIC_SEQ_CST)
+
+/**
+ * Perform a atomic store operation.
+ */
+#define ukarch_store_n(src, value) \
+       __atomic_store_n(src, value, __ATOMIC_SEQ_CST)
+
+/**
+ * Perform a atomic fetch and add operation.
+ */
+#define ukarch_fetch_add(src, value) \
+       __atomic_fetch_add(src, value, __ATOMIC_SEQ_CST)
+
+/**
+ * Perform a atomic increment operation.
+ */
+#define ukarch_inc(src) \
+       ukarch_fetch_add(src, 1)
+
 /**
  * Writes *src into *dst, and returns the previous contents of *dst.
  */
diff --git a/include/uk/arch/types.h b/include/uk/arch/types.h
index a69dc49..9a25336 100644
--- a/include/uk/arch/types.h
+++ b/include/uk/arch/types.h
@@ -261,6 +261,10 @@ typedef __u64 __phys_addr;
 #define __NULL ((void *) 0)
 #endif
 
+typedef struct {
+       __u32 counter;
+} __atomic;
+
 #endif /* !__ASSEMBLY__ */
 
 #ifdef __cplusplus
diff --git a/include/uk/refcount.h b/include/uk/refcount.h
new file mode 100644
index 0000000..fba707c
--- /dev/null
+++ b/include/uk/refcount.h
@@ -0,0 +1,183 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2005 John Baldwin <jhb@xxxxxxxxxxx>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+/* Taken from the Freebsd and modified
+ * commit-id: 81c19620beed0e
+ */
+
+#ifndef __UK_REFCOUNT_H__
+#define __UK_REFCOUNT_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+#include <uk/arch/types.h>
+#include <uk/arch/limits.h>
+#include <uk/arch/atomic.h>
+#include <uk/arch/lcpu.h>
+#include <uk/config.h>
+
+#ifdef CONFIG_LIBUKDEBUG
+#include <uk/assert.h>
+
+#define __refcnt_assert(x) UK_ASSERT(x)
+#else
+#define __refcnt_assert(x) \
+       do {               \
+       } while (0)
+#endif /* CONFIG_LIBUKDEBUG */
+
+/**
+ * Initialize the atomic reference.
+ *
+ * @param ref:
+ *     A reference to the atomic data structure.
+ * @param value:
+ *     A value to initialize.
+ */
+static inline void uk_refcount_init(__atomic *ref, __u32 value)
+{
+       __refcnt_assert(ref != __NULL);
+
+       ukarch_store_n(&ref->counter, value);
+}
+
+/**
+ * Increment the reference counter.
+ * @param refs
+ *     Reference to the atomic counter.
+ */
+static inline void uk_refcount_acquire(__atomic *ref)
+{
+       __refcnt_assert((ref != __NULL) && (ref->counter < __U32_MAX));
+
+       ukarch_inc(&ref->counter);
+}
+
+/**
+ * Decrement the reference counter.
+ * @param refs
+ *     Reference to the atomic counter.
+ * @return
+ *     0: there are more active reference
+ *     1: this was let reference to the counter.
+ */
+static inline int uk_refcount_release(__atomic *ref)
+{
+       __u32 old;
+
+       __refcnt_assert(ref != __NULL);
+
+       /* Compiler Fence */
+       barrier();
+
+       old = ukarch_fetch_add(&ref->counter, -1);
+       __refcnt_assert(old > 0);
+       if (old > 1)
+               return 0;
+
+       /*
+        * Last reference.  Signal the user to call the destructor.
+        *
+        * Ensure that the destructor sees all updates.  The fence_rel
+        * at the start of the function synchronized with this fence.
+        */
+       barrier();
+       return 1;
+}
+
+/**
+ * Increment the reference counter if it was already in use.
+ * @param refs
+ *     Reference to the atomic counter.
+ * @return
+ *     0: Failed to acquire the counter.
+ *     1: Success in acquiring the counter.
+ */
+static inline int uk_refcount_acquire_if_not_zero(__atomic *ref)
+{
+       __u32 old;
+
+       __refcnt_assert(ref != __NULL && ref->counter < __U32_MAX);
+
+       old = ref->counter;
+       for (;;) {
+               if (old == 0)
+                       return 0;
+               if (ukarch_compare_exchange_sync(&ref->counter, old, (old + 1))
+                               == (old + 1))
+                       return 1;
+       }
+}
+
+/**
+ * refcount_read - get a refcount's value
+ * @r: the refcount
+ *
+ * Return: the refcount's value
+ */
+static inline __u32 uk_refcount_read(const __atomic *ref)
+{
+       __refcnt_assert(ref != __NULL);
+
+       return ukarch_load_n(&ref->counter);
+}
+
+
+/**
+ * Decrement the reference counter if there are multiple users of the counter.
+ * @param refs
+ *     Reference to the atomic counter.
+ * @return
+ *     0: Failed to acquire the counter.
+ *     1: Success in acquiring the counter.
+ */
+static inline int uk_refcount_release_if_not_last(__atomic *ref)
+{
+       __u32 old;
+
+       __refcnt_assert(ref != __NULL);
+
+       old = ref->counter;
+       for (;;) {
+               if (old == 1)
+                       return 0;
+               if (ukarch_compare_exchange_sync(&ref->counter, old, (old - 1))
+                               == (old - 1))
+                       return 1;
+       }
+}
+
+#undef __refcnt_assert
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* __UK_REFCOUNT_H__*/
-- 
2.7.4


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