Kernel/PCI: Don't create /proc/pci if PCI is disabled

Reading from /proc/pci assumes we have PCI enabled and also enumerated.
However, if PCI is disabled for some reason, we can't allow the user to
read from it as there's no valuable data we can supply.

Kernel/Bus/PCI/Access.cpp

@@ -17,6 +17,7 @@
 #include <Kernel/Memory/MemoryManager.h>
 #include <Kernel/Memory/Region.h>
 #include <Kernel/Memory/TypedMapping.h>
+#include <Kernel/ProcessExposed.h>
 #include <Kernel/Sections.h>
 
 namespace Kernel::PCI {
@@ -95,6 +96,7 @@ UNMAP_AFTER_INIT bool Access::find_and_register_pci_host_bridges_from_acpi_mcfg_
 UNMAP_AFTER_INIT bool Access::initialize_for_multiple_pci_domains(PhysicalAddress mcfg_table)
 {
     VERIFY(!Access::is_initialized());
+    ProcFSComponentRegistry::the().root_directory().add_pci_node({});
     auto* access = new Access();
     if (!access->find_and_register_pci_host_bridges_from_acpi_mcfg_table(mcfg_table))
         return false;
@@ -106,6 +108,7 @@ UNMAP_AFTER_INIT bool Access::initialize_for_multiple_pci_domains(PhysicalAddres
 UNMAP_AFTER_INIT bool Access::initialize_for_one_pci_domain()
 {
     VERIFY(!Access::is_initialized());
+    ProcFSComponentRegistry::the().root_directory().add_pci_node({});
     auto* access = new Access();
     auto host_bridge = HostBridge::must_create_with_io_access();
     access->add_host_controller(move(host_bridge));

Kernel/GlobalProcessExposed.cpp

@@ -9,6 +9,7 @@
 #include <Kernel/Arch/x86/InterruptDisabler.h>
 #include <Kernel/Arch/x86/ProcessorInfo.h>
 #include <Kernel/Bus/PCI/API.h>
+#include <Kernel/Bus/PCI/Access.h>
 #include <Kernel/CommandLine.h>
 #include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/Devices/HID/HIDManagement.h>
@@ -949,6 +950,11 @@ UNMAP_AFTER_INIT ProcFSSystemDirectory::ProcFSSystemDirectory(const ProcFSRootDi
 {
 }
 
+UNMAP_AFTER_INIT void ProcFSRootDirectory::add_pci_node(Badge<PCI::Access>)
+{
+    m_components.append(ProcFSPCI::must_create());
+}
+
 UNMAP_AFTER_INIT NonnullRefPtr<ProcFSRootDirectory> ProcFSRootDirectory::must_create()
 {
     auto directory = adopt_ref(*new (nothrow) ProcFSRootDirectory);
@@ -961,7 +967,6 @@ UNMAP_AFTER_INIT NonnullRefPtr<ProcFSRootDirectory> ProcFSRootDirectory::must_cr
     directory->m_components.append(ProcFSDmesg::must_create());
     directory->m_components.append(ProcFSInterrupts::must_create());
     directory->m_components.append(ProcFSKeymap::must_create());
-    directory->m_components.append(ProcFSPCI::must_create());
     directory->m_components.append(ProcFSDevices::must_create());
     directory->m_components.append(ProcFSUptime::must_create());
     directory->m_components.append(ProcFSCommandLine::must_create());

Kernel/ProcessExposed.h

@@ -138,12 +138,18 @@ class ProcFSExposedLink : public ProcFSExposedComponent {
     mutable Mutex m_lock { "ProcFSLink" };
 };
 
+namespace PCI {
+class Access;
+}
+
 class ProcFSRootDirectory final : public ProcFSExposedDirectory {
     friend class ProcFSComponentRegistry;
 
 public:
     virtual ErrorOr<NonnullRefPtr<ProcFSExposedComponent>> lookup(StringView name) override;
     static NonnullRefPtr<ProcFSRootDirectory> must_create();
+
+    void add_pci_node(Badge<PCI::Access>);
     virtual ~ProcFSRootDirectory();
 
 private: