From ff952cfe16d37387abb654a3cde79c8f8238150d Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Fri, 2 Jun 2023 21:45:31 +0200
Subject: [PATCH] kernel+init: Let userspace control devfs mountpoints

---
 apps/init.cpp                            | 10 +++++++++
 kernel/src/fs/devices/DeviceRegistry.cpp | 27 +++++++++++++-----------
 kernel/src/fs/devices/DeviceRegistry.h   |  3 +++
 kernel/src/sys/mount.cpp                 | 10 ++++++---
 4 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/apps/init.cpp b/apps/init.cpp
index dbb722ea..786c5305 100644
--- a/apps/init.cpp
+++ b/apps/init.cpp
@@ -10,6 +10,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/mount.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/sysmacros.h>
@@ -258,6 +259,13 @@ static Result<void> set_hostname()
     return {};
 }
 
+static void mount_devfs()
+{
+    if (mkdir("/dev", 0755) < 0 && errno != EEXIST) exit(255);
+
+    if (mount("/dev", "devfs") < 0) exit(255);
+}
+
 int main()
 {
     if (getpid() != 1)
@@ -266,6 +274,8 @@ int main()
         return 1;
     }
 
+    mount_devfs();
+
     // Before this point, we don't even have an stdin, stdout and stderr. Set it up now so that child processes (and us)
     // can print stuff.
     stdin = fopen("/dev/console", "r");
diff --git a/kernel/src/fs/devices/DeviceRegistry.cpp b/kernel/src/fs/devices/DeviceRegistry.cpp
index 1c7a9705..7e1b01a2 100644
--- a/kernel/src/fs/devices/DeviceRegistry.cpp
+++ b/kernel/src/fs/devices/DeviceRegistry.cpp
@@ -21,8 +21,6 @@ struct DeviceDescriptor
 
 Vector<DeviceDescriptor> g_available_devices = {};
 
-SharedPtr<VFS::FileSystem> g_device_fs;
-
 namespace DeviceRegistry
 {
     Result<SharedPtr<Device>> fetch_special_device(u32 major, u32 minor)
@@ -35,11 +33,11 @@ namespace DeviceRegistry
         return err(ENODEV);
     }
 
-    Result<void> create_special_device_inode(DeviceDescriptor& descriptor)
+    Result<void> create_special_device_inode(SharedPtr<VFS::FileSystem> fs, const DeviceDescriptor& descriptor)
     {
-        auto inode = TRY(g_device_fs->create_device_inode(descriptor.major, descriptor.minor));
+        auto inode = TRY(fs->create_device_inode(descriptor.major, descriptor.minor));
         inode->chmod(descriptor.mode);
-        TRY(g_device_fs->root_inode()->add_entry(inode, descriptor.name));
+        TRY(fs->root_inode()->add_entry(inode, descriptor.name));
 
         return {};
     }
@@ -51,23 +49,17 @@ namespace DeviceRegistry
             if (descriptor.major == major && descriptor.minor == minor) return err(EEXIST);
         }
 
-        kdbgln("DeviceRegistry: registered new device type %u:%u at path /dev/%s", major, minor, name);
+        kdbgln("DeviceRegistry: registered new device type %u:%u at path /%s in devfs", major, minor, name);
 
         auto desc = DeviceDescriptor { .device = device, .major = major, .minor = minor, .name = name, .mode = mode };
 
         TRY(g_available_devices.try_append(desc));
 
-        TRY(create_special_device_inode(desc));
-
         return {};
     }
 
     Result<void> init()
     {
-        auto device_fs = TRY(TmpFS::FileSystem::create());
-        TRY(VFS::mount("/dev", device_fs, Credentials {}));
-        g_device_fs = device_fs;
-
         NullDevice::create();
         ZeroDevice::create();
         FullDevice::create();
@@ -82,4 +74,15 @@ namespace DeviceRegistry
         static u32 next_minor = 0;
         return luna_dev_makedev(0, next_minor++);
     }
+
+    // FIXME: This devfs will only contain the devices registered before its creation. Otherwise, created devfs
+    // instances would have to be stored using WeakPtr or something (which doesn't exist atm)...
+    Result<SharedPtr<VFS::FileSystem>> create_devfs_instance()
+    {
+        auto fs = TRY(TmpFS::FileSystem::create());
+
+        for (const auto& descriptor : g_available_devices) TRY(create_special_device_inode(fs, descriptor));
+
+        return fs;
+    }
 }
diff --git a/kernel/src/fs/devices/DeviceRegistry.h b/kernel/src/fs/devices/DeviceRegistry.h
index e698969f..552a78c9 100644
--- a/kernel/src/fs/devices/DeviceRegistry.h
+++ b/kernel/src/fs/devices/DeviceRegistry.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "fs/VFS.h"
 #include "fs/devices/Device.h"
 #include <luna/SharedPtr.h>
 #include <sys/types.h>
@@ -23,4 +24,6 @@ namespace DeviceRegistry
 
     // Used for file systems (like tmpfs) that do not have a host device.
     dev_t next_null_device_id();
+
+    Result<SharedPtr<VFS::FileSystem>> create_devfs_instance();
 }
diff --git a/kernel/src/sys/mount.cpp b/kernel/src/sys/mount.cpp
index bf197b06..661e0187 100644
--- a/kernel/src/sys/mount.cpp
+++ b/kernel/src/sys/mount.cpp
@@ -12,10 +12,14 @@ Result<u64> sys_mount(Registers*, SyscallArgs args)
     auto* current = Scheduler::current();
     if (current->auth.euid != 0) return err(EPERM);
 
-    // Right now we only support one file system.
-    if (fstype.view() != "tmpfs") return err(ENODEV);
+    SharedPtr<VFS::FileSystem> fs;
+
+    if (fstype.view() == "tmpfs") fs = TRY(TmpFS::FileSystem::create());
+    else if (fstype.view() == "devfs")
+        fs = TRY(DeviceRegistry::create_devfs_instance());
+    else
+        return err(ENODEV);
 
-    auto fs = TRY(TmpFS::FileSystem::create());
     TRY(VFS::mount(target.chars(), fs, current->auth, current->current_directory));
 
     return 0;