Use hash func to boost file creation and lookup

Makefile

@@ -1,5 +1,5 @@
 obj-m += simplefs.o
-simplefs-objs := fs.o super.o inode.o file.o dir.o extent.o
+simplefs-objs := fs.o super.o inode.o file.o dir.o extent.o hash.o
 
 KDIR ?= /lib/modules/$(shell uname -r)/build
 

README.md

@@ -97,7 +97,7 @@ named `ei_block`. This field, `ei_block`, serves different purposes depending
 on the type of file:
   - For a directory, it contains the list of files within that directory.
     A directory can hold a maximum of 40,920 files, with filenames restricted
-    to a maximum of 255 characters to ensure they fit within a single block.
+    to a maximum of 254 characters to ensure they fit within a single block.
   ```
   inode
   +-----------------------+

dir.c

@@ -62,9 +62,10 @@ static int simplefs_iterate(struct file *dir, struct dir_context *ctx)
     for (; remained_nr_files && ei < SIMPLEFS_MAX_EXTENTS; ei++) {
         if (eblock->extents[ei].ee_start == 0)
             continue;
-
+        int ei_nr = eblock->extents[ei].nr_files;
         /* Iterate over blocks in one extent */
-        for (bi = 0; bi < eblock->extents[ei].ee_len && remained_nr_files;
+        for (bi = 0;
+             bi < eblock->extents[ei].ee_len && remained_nr_files && ei_nr;
              bi++) {
             bh2 = sb_bread(sb, eblock->extents[ei].ee_start + bi);
             if (!bh2) {
@@ -80,12 +81,13 @@ static int simplefs_iterate(struct file *dir, struct dir_context *ctx)
                 continue;
             }
 
-            for (fi = 0; fi < SIMPLEFS_FILES_PER_BLOCK;) {
+            for (fi = 0; fi < SIMPLEFS_FILES_PER_BLOCK && dblock->nr_files;) {
                 if (dblock->files[fi].inode != 0) {
                     if (offset) {
                         offset--;
                     } else {
                         remained_nr_files--;
+                        ei_nr--;
                         if (!dir_emit(ctx, dblock->files[fi].filename,
                                       SIMPLEFS_FILENAME_LEN,
                                       dblock->files[fi].inode, DT_UNKNOWN)) {

hash.c

@@ -0,0 +1,15 @@
+#include <linux/dcache.h>
+#include <linux/types.h>
+#include "simplefs.h"
+
+uint32_t simplefs_hash(struct dentry *dentry)
+{
+    const char *str = dentry->d_name.name;
+    uint64_t h = 0xcbf29ce484222325ULL;
+    while (*str) {
+        h ^= (unsigned char) (*str++);
+        h *= 0x100000001b3ULL;
+    }
+    /* Fold high 32 bits into low 32 bits to mix the full 64-bit result */
+    return (uint32_t) (h ^ (h >> 32));
+}