Kernel: Merge the shbuf_get_size() syscall into shbuf_get()

Add an extra out-parameter to shbuf_get() that receives the size of the
shared buffer. That way we don't need to make a separate syscall to
get the size, which we always did immediately after.

AK/SharedBuffer.cpp

@@ -67,16 +67,12 @@ bool SharedBuffer::share_globally()
 
 RefPtr<SharedBuffer> SharedBuffer::create_from_shbuf_id(int shbuf_id)
 {
-    void* data = shbuf_get(shbuf_id);
+    size_t size = 0;
+    void* data = shbuf_get(shbuf_id, &size);
     if (data == (void*)-1) {
         perror("shbuf_get");
         return nullptr;
     }
-    int size = shbuf_get_size(shbuf_id);
-    if (size < 0) {
-        perror("shbuf_get_size");
-        return nullptr;
-    }
     return adopt(*new SharedBuffer(shbuf_id, size, data));
 }
 

Kernel/Process.cpp

@@ -3634,9 +3634,11 @@ int Process::sys$shbuf_release(int shbuf_id)
     return 0;
 }
 
-void* Process::sys$shbuf_get(int shbuf_id)
+void* Process::sys$shbuf_get(int shbuf_id, size_t* user_size)
 {
     REQUIRE_PROMISE(shared_buffer);
+    if (user_size && !validate_write_typed(user_size))
+        return (void*)-EFAULT;
     LOCKER(shared_buffers().lock());
     auto it = shared_buffers().resource().find(shbuf_id);
     if (it == shared_buffers().resource().end())
@@ -3647,6 +3649,10 @@ void* Process::sys$shbuf_get(int shbuf_id)
 #ifdef SHARED_BUFFER_DEBUG
     kprintf("%s(%u): Retaining shared buffer %d, buffer count: %u\n", name().characters(), pid(), shbuf_id, shared_buffers().resource().size());
 #endif
+    if (user_size) {
+        size_t size = shared_buffer.size();
+        copy_to_user(user_size, &size);
+    }
     return shared_buffer.ref_for_process_and_get_address(*this);
 }
 
@@ -3667,22 +3673,6 @@ int Process::sys$shbuf_seal(int shbuf_id)
     return 0;
 }
 
-int Process::sys$shbuf_get_size(int shbuf_id)
-{
-    REQUIRE_PROMISE(shared_buffer);
-    LOCKER(shared_buffers().lock());
-    auto it = shared_buffers().resource().find(shbuf_id);
-    if (it == shared_buffers().resource().end())
-        return -EINVAL;
-    auto& shared_buffer = *(*it).value;
-    if (!shared_buffer.is_shared_with(m_pid))
-        return -EPERM;
-#ifdef SHARED_BUFFER_DEBUG
-    kprintf("%s(%u): Get shared buffer %d size: %u\n", name().characters(), pid(), shbuf_id, shared_buffers().resource().size());
-#endif
-    return shared_buffer.size();
-}
-
 int Process::sys$shbuf_set_volatile(int shbuf_id, bool state)
 {
     REQUIRE_PROMISE(shared_buffer);

Kernel/Process.h

@@ -276,10 +276,9 @@ public:
     int sys$shbuf_create(int, void** buffer);
     int sys$shbuf_allow_pid(int, pid_t peer_pid);
     int sys$shbuf_allow_all(int);
-    void* sys$shbuf_get(int shbuf_id);
+    void* sys$shbuf_get(int shbuf_id, size_t* size);
     int sys$shbuf_release(int shbuf_id);
     int sys$shbuf_seal(int shbuf_id);
-    int sys$shbuf_get_size(int shbuf_id);
     int sys$shbuf_set_volatile(int shbuf_id, bool);
     int sys$halt();
     int sys$reboot();

Kernel/Syscall.h

@@ -121,7 +121,6 @@ namespace Kernel {
     __ENUMERATE_SYSCALL(chown)                \
     __ENUMERATE_SYSCALL(fchmod)               \
     __ENUMERATE_SYSCALL(symlink)              \
-    __ENUMERATE_SYSCALL(shbuf_get_size)       \
     __ENUMERATE_SYSCALL(shbuf_seal)           \
     __ENUMERATE_SYSCALL(sendto)               \
     __ENUMERATE_SYSCALL(recvfrom)             \

Libraries/LibC/serenity.h

@@ -34,10 +34,9 @@ __BEGIN_DECLS
 int shbuf_create(int, void** buffer);
 int shbuf_allow_pid(int, pid_t peer_pid);
 int shbuf_allow_all(int);
-void* shbuf_get(int shbuf_id);
+void* shbuf_get(int shbuf_id, size_t* size);
 int shbuf_release(int shbuf_id);
 int shbuf_seal(int shbuf_id);
-int shbuf_get_size(int shbuf_id);
 
 int module_load(const char* path, size_t path_length);
 int module_unload(const char* name, size_t name_length);

Libraries/LibC/unistd.cpp

@@ -553,9 +553,9 @@ int set_process_icon(int icon_id)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-void* shbuf_get(int shbuf_id)
+void* shbuf_get(int shbuf_id, size_t* size)
 {
-    int rc = syscall(SC_shbuf_get, shbuf_id);
+    int rc = syscall(SC_shbuf_get, shbuf_id, size);
     if (rc < 0 && -rc < EMAXERRNO) {
         errno = -rc;
         return (void*)-1;
@@ -569,12 +569,6 @@ int shbuf_release(int shbuf_id)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-int shbuf_get_size(int shbuf_id)
-{
-    int rc = syscall(SC_shbuf_get_size, shbuf_id);
-    __RETURN_WITH_ERRNO(rc, rc, -1);
-}
-
 int shbuf_seal(int shbuf_id)
 {
     int rc = syscall(SC_shbuf_seal, shbuf_id);