Kernel: Deemphasize inode identifiers

These APIs were clearly modeled after Ext2FS internals, and make perfect sense
in Ext2FS context. The new APIs are more generic, and map better to the
semantics exported to the userspace, where inode identifiers only appear in
stat() and readdir() output, but never in any input.

This will also hopefully reduce the potential for races (see commit https://github.com/SerenityOS/serenity/commit/c44b4d61f350703fcf1bbd8f6e353b9c6c4210c2).

Lastly, this makes it way more viable to implement a filesystem that only
synthesizes its inodes lazily when queried, and destroys them when they are no
longer in use. With inode identifiers being used to reference inodes, the only
choice for such a filesystem is to persist any inode it has given out the
identifier for, because it might be queried at any later time. With direct
references to inodes, the filesystem will know when the last reference is
dropped and the inode can be safely destroyed.

1 files changed, 47 insertions, 66 deletions

diff --git a/Kernel/FileSystem/TmpFS.cpp b/Kernel/FileSystem/TmpFS.cpp
index 86d141010a..66dec6e272 100644
--- a/Kernel/FileSystem/TmpFS.cpp
+++ b/Kernel/FileSystem/TmpFS.cpp
@@ -49,10 +49,11 @@ bool TmpFS::initialize()
     return true;
 }
 
-InodeIdentifier TmpFS::root_inode() const
+NonnullRefPtr<Inode> TmpFS::root_inode() const
 {
     ASSERT(!m_root_inode.is_null());
-    return m_root_inode->identifier();
+
+    return *m_root_inode;
 }
 
 void TmpFS::register_inode(TmpFSInode& inode)
@@ -90,49 +91,6 @@ RefPtr<Inode> TmpFS::get_inode(InodeIdentifier identifier) const
     return it->value;
 }
 
-KResultOr<NonnullRefPtr<Inode>> TmpFS::create_inode(InodeIdentifier parent_id, const String& name, mode_t mode, off_t size, dev_t dev, uid_t uid, gid_t gid)
-{
-    LOCKER(m_lock);
-    ASSERT(parent_id.fsid() == fsid());
-
-    ASSERT(size == 0);
-    ASSERT(dev == 0);
-
-    struct timeval now;
-    kgettimeofday(now);
-
-    InodeMetadata metadata;
-    metadata.mode = mode;
-    metadata.uid = uid;
-    metadata.gid = gid;
-    metadata.atime = now.tv_sec;
-    metadata.ctime = now.tv_sec;
-    metadata.mtime = now.tv_sec;
-
-    auto inode = TmpFSInode::create(*this, metadata, parent_id);
-
-    auto it = m_inodes.find(parent_id.index());
-    ASSERT(it != m_inodes.end());
-    auto parent_inode = it->value;
-
-    auto result = parent_inode->add_child(inode->identifier(), name, mode);
-    if (result.is_error())
-        return result;
-
-    return inode;
-}
-
-KResult TmpFS::create_directory(InodeIdentifier parent_id, const String& name, mode_t mode, uid_t uid, gid_t gid)
-{
-    // Ensure it's a directory.
-    mode &= ~S_IFMT;
-    mode |= S_IFDIR;
-    auto result = create_inode(parent_id, name, mode, 0, 0, uid, gid);
-    if (result.is_error())
-        return result.error();
-    return KSuccess;
-}
-
 TmpFSInode::TmpFSInode(TmpFS& fs, InodeMetadata metadata, InodeIdentifier parent)
     : Inode(fs, fs.next_inode_index())
     , m_metadata(metadata)
@@ -251,7 +209,7 @@ RefPtr<Inode> TmpFSInode::lookup(StringView name)
     ASSERT(is_directory());
 
     if (name == ".")
-        return fs().get_inode(identifier());
+        return this;
     if (name == "..")
         return fs().get_inode(m_parent);
 
@@ -268,6 +226,12 @@ size_t TmpFSInode::directory_entry_count() const
     return 2 + m_children.size();
 }
 
+void TmpFSInode::notify_watchers()
+{
+    set_metadata_dirty(true);
+    set_metadata_dirty(false);
+}
+
 void TmpFSInode::flush_metadata()
 {
     // We don't really have any metadata that could become dirty.
@@ -283,8 +247,7 @@ KResult TmpFSInode::chmod(mode_t mode)
     LOCKER(m_lock);
 
     m_metadata.mode = mode;
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    notify_watchers();
     return KSuccess;
 }
 
@@ -294,25 +257,47 @@ KResult TmpFSInode::chown(uid_t uid, gid_t gid)
 
     m_metadata.uid = uid;
     m_metadata.gid = gid;
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    notify_watchers();
     return KSuccess;
 }
 
-KResult TmpFSInode::add_child(InodeIdentifier child_id, const StringView& name, mode_t)
+KResultOr<NonnullRefPtr<Inode>> TmpFSInode::create_child(const String& name, mode_t mode, dev_t dev, uid_t uid, gid_t gid)
+{
+    LOCKER(m_lock);
+
+    // TODO: Support creating devices on TmpFS.
+    if (dev != 0)
+        return KResult(-ENOTSUP);
+
+    struct timeval now;
+    kgettimeofday(now);
+
+    InodeMetadata metadata;
+    metadata.mode = mode;
+    metadata.uid = uid;
+    metadata.gid = gid;
+    metadata.atime = now.tv_sec;
+    metadata.ctime = now.tv_sec;
+    metadata.mtime = now.tv_sec;
+
+    auto child = TmpFSInode::create(fs(), metadata, identifier());
+    auto result = add_child(child, name, mode);
+    if (result.is_error())
+        return result;
+    return child;
+}
+
+KResult TmpFSInode::add_child(Inode& child, const StringView& name, mode_t)
 {
     LOCKER(m_lock);
     ASSERT(is_directory());
-    ASSERT(child_id.fsid() == fsid());
+    ASSERT(child.fsid() == fsid());
 
     String owned_name = name;
-    FS::DirectoryEntry entry = { owned_name.characters(), owned_name.length(), child_id, 0 };
-    auto child_tmp = fs().get_inode(child_id);
-    auto child = static_ptr_cast<TmpFSInode>(child_tmp.release_nonnull());
+    FS::DirectoryEntry entry = { owned_name.characters(), owned_name.length(), child.identifier(), 0 };
 
-    m_children.set(owned_name, { entry, move(child) });
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    m_children.set(owned_name, { entry, static_cast<TmpFSInode&>(child) });
+    notify_watchers();
     return KSuccess;
 }
 
@@ -328,8 +313,7 @@ KResult TmpFSInode::remove_child(const StringView& name)
     if (it == m_children.end())
         return KResult(-ENOENT);
     m_children.remove(it);
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    notify_watchers();
     return KSuccess;
 }
 
@@ -356,8 +340,7 @@ KResult TmpFSInode::truncate(u64 size)
 
     size_t old_size = m_metadata.size;
     m_metadata.size = size;
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    notify_watchers();
 
     if (old_size != (size_t)size) {
         inode_size_changed(old_size, size);
@@ -383,8 +366,7 @@ int TmpFSInode::set_ctime(time_t time)
     LOCKER(m_lock);
 
     m_metadata.ctime = time;
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    notify_watchers();
     return KSuccess;
 }
 
@@ -393,8 +375,7 @@ int TmpFSInode::set_mtime(time_t time)
     LOCKER(m_lock);
 
     m_metadata.mtime = time;
-    set_metadata_dirty(true);
-    set_metadata_dirty(false);
+    notify_watchers();
     return KSuccess;
 }