From 6f1a62a173a28b29f10f0dd3a3bae164a9246a66 Mon Sep 17 00:00:00 2001
From: Seiyeon Cho <baekrang256@gmail.com>
Date: Wed, 24 Apr 2024 12:27:18 +0900
Subject: [PATCH 1/3] Use binary search for searching extent

---
 extent.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 60 insertions(+), 10 deletions(-)

diff --git a/extent.c b/extent.c
index cef8b0a..c371f81 100644
--- a/extent.c
+++ b/extent.c
@@ -6,19 +6,69 @@
 /* Search for the extent containing the target block.
  * Returns the first unused file index if not found.
  * Returns -1 if the target block is out of range.
- * TODO: Implement binary search for efficiency.
+ * Binary search is used for efficiency.
  */
 uint32_t simplefs_ext_search(struct simplefs_file_ei_block *index,
                              uint32_t iblock)
 {
-    uint32_t i;
-    for (i = 0; i < SIMPLEFS_MAX_EXTENTS; i++) {
-        uint32_t block = index->extents[i].ee_block;
-        uint32_t len = index->extents[i].ee_len;
-        if (index->extents[i].ee_start == 0 ||
-            (iblock >= block && iblock < block + len))
-            return i;
+    /* first, find the first unused file index with binary search.
+     * It'll be our right boundary for actual binary search
+     * and return value when file index is not found.
+     */
+    uint32_t start = 0;
+    uint32_t end = SIMPLEFS_MAX_EXTENTS - 1;
+    uint32_t boundary;
+    uint32_t end_block;
+    uint32_t end_len;
+
+    while (start < end) {
+        uint32_t mid = start + (end - start) / 2;
+        if (index->extents[mid].ee_start == 0) {
+            end = mid;
+        } else {
+            start = mid + 1;
+        }
+    }
+
+    if (index->extents[end].ee_start == 0) {
+        boundary = end;
+    } else {
+        /* File index full */
+        boundary = end + 1;
+    }
+
+    if (boundary == 0) {
+        /* No used file index */
+        return boundary;
+    }
+
+    /* try finding target block using binary search */
+    start = 0;
+    end = boundary - 1;
+    while (start < end) {
+        uint32_t mid = start + (end - start) / 2;
+        uint32_t block = index->extents[mid].ee_block;
+        uint32_t len = index->extents[mid].ee_len;
+        if (iblock >= block && iblock < block + len) {
+            /* found before search finished */
+            return mid;
+        }
+        if (iblock < block) {
+            end = mid;
+        } else {
+            start = mid + 1;
+        }
     }
 
-    return -1;
-}
+    /* return 'end' if it directs to valid block
+     * return 'boundary' if index is not found
+     * and eiblock has remaining space */
+    end_block = index->extents[end].ee_block;
+    end_len = index->extents[end].ee_len;
+    if (iblock >= end_block && iblock < end_len) {
+        return end;
+    } else if (boundary < SIMPLEFS_MAX_EXTENTS) {
+        return boundary;
+    }
+    return boundary;
+}
\ No newline at end of file

From 6bcbe74d375129fd2232d49362cc6725a8dea9e9 Mon Sep 17 00:00:00 2001
From: "Tse-Chia.Chang" <merqqcury@gmail.com>
Date: Thu, 2 May 2024 22:41:46 +0800
Subject: [PATCH 2/3] Fix typo

---
 simplefs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/simplefs.h b/simplefs.h
index 29fa3d9..84d5e60 100644
--- a/simplefs.h
+++ b/simplefs.h
@@ -123,7 +123,7 @@ extern const struct address_space_operations simplefs_aops;
 extern uint32_t simplefs_ext_search(struct simplefs_file_ei_block *index,
                                     uint32_t iblock);
 
-/* Getters for superbock and inode */
+/* Getters for superblock and inode */
 #define SIMPLEFS_SB(sb) (sb->s_fs_info)
 #define SIMPLEFS_INODE(inode) \
     (container_of(inode, struct simplefs_inode_info, vfs_inode))

From 56ea86a1df6e1063f09fdb24599b7b5a4ed085d6 Mon Sep 17 00:00:00 2001
From: "Tse-Chia.Chang" <merqqcury@gmail.com>
Date: Fri, 3 May 2024 12:12:33 +0800
Subject: [PATCH 3/3] Fix errors raised by missing-prototypes

Fix compile time errors "no previous prototype for simplefs_mount"
and "no previous prototype for simplefs_kill_sb"
---
 simplefs.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/simplefs.h b/simplefs.h
index 84d5e60..158468d 100644
--- a/simplefs.h
+++ b/simplefs.h
@@ -108,12 +108,19 @@ struct simplefs_dir_block {
 
 /* superblock functions */
 int simplefs_fill_super(struct super_block *sb, void *data, int silent);
+void simplefs_kill_sb(struct super_block *sb);
 
 /* inode functions */
 int simplefs_init_inode_cache(void);
 void simplefs_destroy_inode_cache(void);
 struct inode *simplefs_iget(struct super_block *sb, unsigned long ino);
 
+/* dentry function */
+struct dentry *simplefs_mount(struct file_system_type *fs_type,
+                              int flags,
+                              const char *dev_name,
+                              void *data);
+
 /* file functions */
 extern const struct file_operations simplefs_file_ops;
 extern const struct file_operations simplefs_dir_ops;