Use hash func to boost file creation and lookup

Introduce a hash-based mechanism to speed up file creation and lookup
operations. The hash function enables faster access to extent and logical
block extent index, improving overall filesystem performance.

hash_code = file_hash(file_name);
extent index = hash_code / SIMPLEFS_MAX_BLOCKS_PER_EXTENT
block index = hash_code % SIMPLEFS_MAX_BLOCKS_PER_EXTENT;

Use perf to measure:
1. File Creation (random)
Legacy:
259.842753513 seconds time elapsed
23.000247000 seconds user
150.380145000 seconds sys

full_name_hash:
222.274028604 seconds time elapsed
20.794966000 seconds user
151.941876000 seconds sys

2. File Listing (random)
Legacy:
min time: 0.00171 s
max time: 0.03799 s
avg time: 0.00423332 s
tot time: 129.539510 s

full_name_hash:
min time: 0.00171 s
max time: 0.03588 s
avg time: 0.00305601 s
tot time: 93.514040 s

3. files Removal (Random)
Legacy:
106.921706288 seconds time elapsed
16.987883000 seconds user
91.268661000 seconds sys

full_name_hash:
86.132655220 seconds time elapsed
19.180209000 seconds user
68.476075000 seconds sys

Author: RoyWFHuang

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
 

dir.c

@@ -81,7 +81,7 @@ 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--;

hash.c

@@ -0,0 +1,9 @@
+#include <linux/stringhash.h>
+#include <linux/types.h>
+#include "simplefs.h"
+
+uint32_t simplefs_hash(struct dentry *dentry)
+{
+    return full_name_hash(dentry, dentry->d_name.name,
+                          strlen(dentry->d_name.name));
+}