kernel: Implement st_dev and st_rdev

kernel/src/fs/VFS.h

@@ -1,4 +1,5 @@
 #pragma once
+#include <bits/makedev.h>
 #include <luna/SharedPtr.h>
 #include <luna/StaticString.h>
 #include <luna/StringView.h>
@@ -48,6 +49,8 @@ namespace VFS
             m_handles--;
         }
 
+        virtual dev_t host_device_id() const = 0;
+
         virtual ~FileSystem() = default;
 
       protected:
@@ -101,6 +104,11 @@ namespace VFS
             return StringView {};
         }
 
+        virtual dev_t device_id() const
+        {
+            return luna_dev_makedev(0, 0);
+        }
+
         // Metadata accessors
         virtual usize size() const = 0;
 

kernel/src/fs/devices/DeviceRegistry.cpp

@@ -74,4 +74,10 @@ namespace DeviceRegistry
 
         return {};
     }
+
+    dev_t next_null_device_id()
+    {
+        static u32 next_minor = 0;
+        return luna_dev_makedev(0, next_minor++);
+    }
 }

kernel/src/fs/devices/DeviceRegistry.h

@@ -20,4 +20,7 @@ namespace DeviceRegistry
                                          mode_t mode = 0666);
 
     Result<void> init();
+
+    // Used for file systems (like tmpfs) that do not have a host device.
+    dev_t next_null_device_id();
 }

kernel/src/fs/tmpfs/FileSystem.cpp

@@ -55,10 +55,18 @@ namespace TmpFS
         inode->set_fs(*this, {});
         inode->set_inode_number(m_next_inode_number++, {});
         inode->set_device(device, {});
+        // FIXME: This should be queried from Device directly, but Device doesn't have an API to store and retrieve its
+        // device ID atm.
+        inode->set_device_id(luna_dev_makedev(major, minor), {});
 
         return (SharedPtr<VFS::Inode>)inode;
     }
 
+    FileSystem::FileSystem()
+    {
+        m_host_device_id = DeviceRegistry::next_null_device_id();
+    }
+
     Result<void> FileSystem::set_mount_dir(SharedPtr<VFS::Inode> parent)
     {
         return m_root_inode->replace_entry(parent, "..");

kernel/src/fs/tmpfs/FileSystem.h

@@ -27,16 +27,23 @@ namespace TmpFS
 
         static Result<SharedPtr<VFS::FileSystem>> create();
 
+        dev_t host_device_id() const override
+        {
+            return m_host_device_id;
+        }
+
         virtual ~FileSystem() = default;
 
       private:
-        FileSystem() = default;
+        FileSystem();
 
         void set_root(SharedPtr<VFS::Inode> root);
 
         SharedPtr<VFS::Inode> m_root_inode;
 
         Atomic<usize> m_next_inode_number { 2 };
+
+        dev_t m_host_device_id;
     };
 
     class FileInode : public VFS::FileInode
@@ -251,11 +258,21 @@ namespace TmpFS
             m_device = device;
         }
 
+        void set_device_id(dev_t id, Badge<FileSystem>)
+        {
+            m_device_id = id;
+        }
+
         VFS::FileSystem* fs() const override
         {
             return m_fs;
         }
 
+        dev_t device_id() const override
+        {
+            return m_device_id;
+        }
+
         usize inode_number() const override
         {
             return m_inode_number;
@@ -340,6 +357,7 @@ namespace TmpFS
         u32 m_uid { 0 };
         u32 m_gid { 0 };
         u32 m_nlinks { 0 };
+        dev_t m_device_id { 0 };
     };
 
     class DirInode : public VFS::Inode

kernel/src/sys/stat.cpp

@@ -40,6 +40,8 @@ Result<u64> sys_fstatat(Registers*, SyscallArgs args)
     kstat.st_uid = inode->uid();
     kstat.st_gid = inode->gid();
     kstat.st_size = inode->size();
+    kstat.st_dev = inode->fs()->host_device_id();
+    kstat.st_rdev = inode->device_id();
 
     if (!MemoryManager::copy_to_user_typed(st, &kstat)) return err(EFAULT);
 

libc/include/bits/struct_stat.h

@@ -10,9 +10,11 @@ struct stat
     ino_t st_ino;
     mode_t st_mode;
     nlink_t st_nlink;
+    dev_t st_dev;
     uid_t st_uid;
     gid_t st_gid;
     off_t st_size;
+    dev_t st_rdev;
 };
 
 #endif