Kernel/SysFS: Make it possible to have custom permissions for nodes

Author: https://github.com/supercomputer7
Commit: https://github.com/SerenityOS/serenity/commit/06e95d0fd74
Pull-request: https://github.com/SerenityOS/serenity/pull/9958

Kernel/FileSystem/SysFS.cpp

@@ -140,7 +140,7 @@ InodeMetadata SysFSInode::metadata() const
     // NOTE: No locking required as m_associated_component or its component index will never change during our lifetime.
     InodeMetadata metadata;
     metadata.inode = { fsid(), m_associated_component->component_index() };
-    metadata.mode = S_IFREG | S_IRUSR | S_IRGRP | S_IROTH;
+    metadata.mode = S_IFREG | m_associated_component->permissions();
     metadata.uid = 0;
     metadata.gid = 0;
     metadata.size = 0;

Kernel/FileSystem/SysFSComponent.cpp

@@ -26,6 +26,11 @@ SysFSComponent::SysFSComponent(StringView name)
 {
 }
 
+mode_t SysFSComponent::permissions() const
+{
+    return S_IRUSR | S_IRGRP | S_IROTH;
+}
+
 KResult SysFSDirectory::traverse_as_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
 {
     MutexLocker locker(SysFSComponentRegistry::the().get_lock());

Kernel/FileSystem/SysFSComponent.h

@@ -29,6 +29,7 @@ public:
     virtual KResultOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer&, OpenFileDescription*) const { VERIFY_NOT_REACHED(); }
     virtual KResult traverse_as_directory(unsigned, Function<bool(FileSystem::DirectoryEntryView const&)>) const { VERIFY_NOT_REACHED(); }
     virtual RefPtr<SysFSComponent> lookup(StringView) { VERIFY_NOT_REACHED(); };
+    virtual mode_t permissions() const;
     virtual KResultOr<size_t> write_bytes(off_t, size_t, UserOrKernelBuffer const&, OpenFileDescription*) { return EROFS; }
     virtual KResult refresh_data(OpenFileDescription&) const { return KSuccess; }