1 files changed, 287 insertions, 0 deletions
diff --git a/fs/dcache.cc b/fs/dcache.cc
new file mode 100644
index 0000000..94ab287
--- /dev/null
+++ b/fs/dcache.cc
@@ -0,0 +1,287 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * dcache.cc — Directory entry cache
+ *
+ * Provides dentry allocation, lookup, instantiation, and d_path.
+ */
+
+#include <lume/dcache.h>
+#include <lume/fs.h>
+#include <lume/file.h>
+#include <lume/slab.h>
+#include <lume/errno.h>
+#include <lume/fs_types.h>
+
+/* ================================================================== */
+/*  Hash function                                                     */
+/* ================================================================== */
+
+uint32 full_name_hash(const char* name, uint32 len)
+{
+    uint32 hash = 0;
+    for (uint32 i = 0; i < len; i++)
+        hash = hash * 31 + static_cast<uint8>(name[i]);
+    return hash;
+}
+
+/* ================================================================== */
+/*  d_set_type — set DCACHE_*_TYPE bits from inode mode               */
+/* ================================================================== */
+
+void d_set_type(dentry* de, uint32 i_mode)
+{
+    de->d_flags &= ~DCACHE_ENTRY_TYPE;
+
+    if (S_ISDIR(i_mode))
+        de->d_flags |= DCACHE_DIRECTORY_TYPE;
+    else if (S_ISLNK(i_mode))
+        de->d_flags |= DCACHE_SYMLINK_TYPE;
+    else if (S_ISREG(i_mode))
+        de->d_flags |= DCACHE_REGULAR_TYPE;
+    else
+        de->d_flags |= DCACHE_SPECIAL_TYPE;
+}
+
+/* ================================================================== */
+/*  d_alloc — allocate a dentry under a parent                        */
+/* ================================================================== */
+
+static void dentry_init(dentry* de, dentry* parent, const qstr* name)
+{
+    de->d_flags = DCACHE_MISS_TYPE;  /* negative until instantiated */
+    de->d_parent = parent ? parent : de;
+    de->d_inode = nullptr;
+    de->d_op = nullptr;
+    de->d_sb = parent ? parent->d_sb : nullptr;
+    de->d_time = 0;
+    de->d_fsdata = nullptr;
+    de->d_lockref.store(1);
+
+    list_init(&de->d_lru);
+    list_init(&de->d_child);
+    list_init(&de->d_children);
+    list_init(&de->d_alias);
+
+    /* Copy name */
+    if (name && name->name && name->len > 0) {
+        uint32 len = name->len;
+        if (len < DNAME_INLINE_LEN) {
+            for (uint32 i = 0; i < len; i++)
+                de->d_iname[i] = name->name[i];
+            de->d_iname[len] = '\0';
+            de->d_name.name = reinterpret_cast<const char*>(de->d_iname);
+        } else {
+            /* Heap-allocate for long names */
+            char* buf = new char[len + 1];
+            for (uint32 i = 0; i < len; i++)
+                buf[i] = name->name[i];
+            buf[len] = '\0';
+            de->d_name.name = buf;
+        }
+        de->d_name.len = len;
+        de->d_name.hash = name->hash ? name->hash : full_name_hash(name->name, len);
+    } else {
+        de->d_iname[0] = '\0';
+        de->d_name.name = reinterpret_cast<const char*>(de->d_iname);
+        de->d_name.len = 0;
+        de->d_name.hash = 0;
+    }
+}
+
+dentry* d_alloc(dentry* parent, const qstr* name)
+{
+    auto* de = new dentry{};
+    if (!de) return nullptr;
+
+    dentry_init(de, parent, name);
+    de->d_sb = parent->d_sb;
+
+    /* Use sb default d_op if set */
+    if (parent->d_sb->s_d_op)
+        de->d_op = parent->d_sb->s_d_op;
+
+    /* Link into parent's children list */
+    if (parent) {
+        LockGuard guard(parent->d_lock);
+        list_add_tail(&de->d_child, &parent->d_children);
+        dget(parent);  /* child holds ref on parent */
+    }
+
+    return de;
+}
+
+dentry* d_alloc_anon(super_block* sb)
+{
+    auto* de = new dentry{};
+    if (!de) return nullptr;
+
+    dentry_init(de, nullptr, nullptr);
+    de->d_sb = sb;
+    de->d_parent = de;  /* root: parent is self */
+
+    return de;
+}
+
+/* ================================================================== */
+/*  d_instantiate — bind an inode to a dentry                         */
+/* ================================================================== */
+
+void d_instantiate(dentry* de, inode* ip)
+{
+    if (!ip) return;
+
+    LockGuard guard(de->d_lock);
+    de->d_inode = ip;
+    d_set_type(de, ip->i_mode);
+
+    /* Add to inode's alias list */
+    list_add_tail(&de->d_alias, &ip->i_dentry);
+}
+
+/* ================================================================== */
+/*  d_make_root — create root dentry for a superblock                 */
+/* ================================================================== */
+
+dentry* d_make_root(inode* root_inode)
+{
+    if (!root_inode) return nullptr;
+
+    dentry* de = d_alloc_anon(root_inode->i_sb);
+    if (!de) {
+        iput(root_inode);
+        return nullptr;
+    }
+
+    d_instantiate(de, root_inode);
+    return de;
+}
+
+/* ================================================================== */
+/*  d_add — combined d_instantiate + d_rehash                         */
+/* ================================================================== */
+
+void d_add(dentry* de, inode* ip)
+{
+    d_instantiate(de, ip);
+    /* d_rehash would add to dcache hash table; simplified for now */
+}
+
+/* ================================================================== */
+/*  d_lookup — search children of parent for a name match             */
+/* ================================================================== */
+
+dentry* d_lookup(const dentry* parent, const qstr* name)
+{
+    LockGuard guard(const_cast<Spinlock&>(parent->d_lock));
+
+    list_node* pos;
+    list_for_each(pos, &parent->d_children) {
+        dentry* child = list_entry(pos, dentry, d_child);
+
+        if (child->d_name.len != name->len)
+            continue;
+
+        /* Compare names */
+        const char* a = child->d_name.name;
+        const char* b = name->name;
+        uint32 len = name->len;
+        bool match = true;
+        for (uint32 i = 0; i < len; i++) {
+            if (a[i] != b[i]) { match = false; break; }
+        }
+        if (match) {
+            dget(child);
+            return child;
+        }
+    }
+
+    return nullptr;
+}
+
+/* ================================================================== */
+/*  dget / dput — dentry reference counting                           */
+/* ================================================================== */
+
+dentry* dget(dentry* de)
+{
+    if (de)
+        de->d_lockref.fetch_add(1);
+    return de;
+}
+
+void dput(dentry* de)
+{
+    if (!de) return;
+
+    int old = de->d_lockref.fetch_sub(1);
+    if (old > 1) return;
+
+    /* Last reference — could free, but for ramfs we keep dentries alive.
+     * A real implementation would check d_op->d_delete and possibly
+     * add to LRU for later reclaim. For now, just leak (Phase 1). */
+}
+
+/* ================================================================== */
+/*  d_drop / d_delete                                                 */
+/* ================================================================== */
+
+void d_drop(dentry* de)
+{
+    /* Remove from parent's children list */
+    LockGuard guard(de->d_lock);
+    if (!list_empty(&de->d_child))
+        list_del_init(&de->d_child);
+}
+
+void d_delete(dentry* de)
+{
+    d_drop(de);
+}
+
+/* ================================================================== */
+/*  d_path — build absolute pathname from a path                      */
+/* ================================================================== */
+
+char* d_path(const path* p, char* buf, int buflen)
+{
+    if (!p || !p->de || buflen <= 0)
+        return nullptr;
+
+    /* Build path by walking up d_parent chain, writing backwards */
+    char* end = buf + buflen - 1;
+    *end = '\0';
+
+    dentry* de = p->de;
+
+    if (d_is_root(de)) {
+        if (end <= buf) return nullptr;
+        *(--end) = '/';
+        return end;
+    }
+
+    while (!d_is_root(de)) {
+        uint32 len = de->d_name.len;
+        end -= len;
+        if (end <= buf) return nullptr;
+
+        const char* name = de->d_name.name;
+        for (uint32 i = 0; i < len; i++)
+            end[i] = name[i];
+
+        *(--end) = '/';
+        de = de->d_parent;
+    }
+
+    return end;
+}
+
+/* ================================================================== */
+/*  dcache_init                                                       */
+/* ================================================================== */
+
+void dcache_init()
+{
+    /* Future: init dcache hash table */
+}