Add a C++ helper class for working with shared buffers.

This is a bit more comfortable than passing the shared buffer ID manually
everywhere and keeping track of size etc.

LibC/Makefile

@@ -7,6 +7,7 @@ AK_OBJS = \
     ../AK/kmalloc.o
 
 LIBC_OBJS = \
+       SharedBuffer.o \
        stdio.o \
        unistd.o \
        string.o \

LibC/SharedBuffer.cpp

@@ -0,0 +1,55 @@
+#include <LibC/SharedBuffer.h>
+#include <unistd.h>
+#include <stdio.h>
+
+RetainPtr<SharedBuffer> SharedBuffer::create(pid_t peer, int size)
+{
+    void* data;
+    int shared_buffer_id = create_shared_buffer(peer, size, &data);
+    if (shared_buffer_id < 0) {
+        perror("create_shared_buffer");
+        return nullptr;
+    }
+    return adopt(*new SharedBuffer(shared_buffer_id, size, data));
+}
+
+RetainPtr<SharedBuffer> SharedBuffer::create_from_shared_buffer_id(int shared_buffer_id)
+{
+    void* data = get_shared_buffer(shared_buffer_id);
+    if (data == (void*)-1) {
+        perror("get_shared_buffer");
+        return nullptr;
+    }
+    int size = get_shared_buffer_size(shared_buffer_id);
+    if (size < 0) {
+        perror("get_shared_buffer_size");
+        return nullptr;
+    }
+    return adopt(*new SharedBuffer(shared_buffer_id, size, data));
+}
+
+SharedBuffer::SharedBuffer(int shared_buffer_id, int size, void* data)
+    : m_shared_buffer_id(shared_buffer_id)
+    , m_size(size)
+    , m_data(data)
+{
+}
+
+SharedBuffer::~SharedBuffer()
+{
+    if (m_shared_buffer_id >= 0) {
+        int rc = release_shared_buffer(m_shared_buffer_id);
+        if (rc < 0) {
+            perror("release_shared_buffer");
+        }
+    }
+}
+
+void SharedBuffer::seal()
+{
+    int rc = seal_shared_buffer(m_shared_buffer_id);
+    if (rc < 0) {
+        perror("seal_shared_buffer");
+        exit(1);
+    }
+}

LibC/SharedBuffer.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <AK/Retainable.h>
+#include <AK/RetainPtr.h>
+
+class SharedBuffer : public Retainable<SharedBuffer> {
+public:
+    static RetainPtr<SharedBuffer> create(pid_t peer, int);
+    static RetainPtr<SharedBuffer> create_from_shared_buffer_id(int);
+    ~SharedBuffer();
+
+    int shared_buffer_id() const { return m_shared_buffer_id; }
+    void seal();
+    int size() const { return m_size; }
+    void* data() { return m_data; }
+    const void* data() const { return m_data; }
+
+private:
+    SharedBuffer(int shared_buffer_id, int size, void*);
+
+    int m_shared_buffer_id { -1 };
+    int m_size { 0 };
+    void* m_data;
+};

LibC/unistd.cpp

@@ -361,7 +361,7 @@ int read_tsc(unsigned* lsw, unsigned* msw)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-int create_shared_buffer(pid_t peer_pid, size_t size, void** buffer)
+int create_shared_buffer(pid_t peer_pid, int size, void** buffer)
 {
     int rc = syscall(SC_create_shared_buffer, peer_pid, size, buffer);
     __RETURN_WITH_ERRNO(rc, rc, -1);
@@ -383,6 +383,18 @@ int release_shared_buffer(int shared_buffer_id)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
+int get_shared_buffer_size(int shared_buffer_id)
+{
+    int rc = syscall(SC_get_shared_buffer_size, shared_buffer_id);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
+int seal_shared_buffer(int shared_buffer_id)
+{
+    int rc = syscall(SC_seal_shared_buffer, shared_buffer_id);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
 char* getlogin()
 {
     assert(false);

LibC/unistd.h

@@ -14,9 +14,11 @@ __BEGIN_DECLS
 
 extern char** environ;
 
-int create_shared_buffer(pid_t peer_pid, size_t, void** buffer);
+int create_shared_buffer(pid_t peer_pid, int, void** buffer);
 void* get_shared_buffer(int shared_buffer_id);
 int release_shared_buffer(int shared_buffer_id);
+int seal_shared_buffer(int shared_buffer_id);
+int get_shared_buffer_size(int shared_buffer_id);
 int read_tsc(unsigned* lsw, unsigned* msw);
 inline int getpagesize() { return 4096; }
 pid_t fork();