Fix missing data synchronization

The get_free_blocks function in simplefs has an issue where data
written to the disk is not being properly synchronized.

Testing:
The test flow is as follow. After step 4 the content of test.txt
is empty.
1. mount simplefs
2. vim test.txt
3. umount
4. mount

Changes:
Add sync_dirty_buffer to ensure proper disk synchronization.
Add automated tests for checking the data consistency.

Author: HotMercury

bitmap.h

@@ -47,11 +47,12 @@ static inline uint32_t get_free_blocks(struct super_block *sb, uint32_t len)
 {
     struct simplefs_sb_info *sbi = SIMPLEFS_SB(sb);
     uint32_t ret = get_first_free_bits(sbi->bfree_bitmap, sbi->nr_blocks, len);
+    uint32_t i;
     if (!ret) /* No enough free blocks */
         return 0;
 
     sbi->nr_free_blocks -= len;
-    for (uint32_t i = 0; i < len; i++) {
+    for (i = 0; i < len; i++) {
         struct buffer_head *bh = sb_bread(sb, ret + i);
         if (!bh) {
             pr_err("get_free_blocks: sb_bread failed for block %d\n", ret + i);
@@ -60,6 +61,7 @@ static inline uint32_t get_free_blocks(struct super_block *sb, uint32_t len)
         }
         memset(bh->b_data, 0, SIMPLEFS_BLOCK_SIZE);
         mark_buffer_dirty(bh);
+        sync_dirty_buffer(bh); /* write the buffer to disk */
         brelse(bh);
     }
     return ret;

script/test.sh

@@ -10,6 +10,7 @@ F_MOD="-rw-r--r--"
 S_MOD="lrwxrwxrwx"
 MAXFILESIZE=11173888 # SIMPLEFS_MAX_EXTENTS * SIMPLEFS_MAX_BLOCKS_PER_EXTENT * SIMPLEFS_BLOCK_SIZE
 MAXFILES=40920        # max files per dir
+MOUNT_TEST=100
 
 test_op() {
     local op=$1 
@@ -61,6 +62,42 @@ done
 filecnts=$(ls | wc -w)
 test $filecnts -eq $MAXFILES || echo "Failed, it should be $MAXFILES files"
 find . -name '[0-9]*.txt' | xargs -n 2000 sudo rm
+sync
+
+# create 100 files with filenames inside
+for ((i=1; i<=$MOUNT_TEST; i++))
+do
+    echo file_$i | sudo tee file_$i.txt >/dev/null && echo "file_$i.txt created."
+done
+sync
+
+# unmount and remount the filesystem
+echo "Unmounting filesystem..."
+popd >/dev/null || { echo "popd failed"; exit 1; }
+sudo umount test || { echo "umount failed"; exit 1; }
+sleep 1
+echo "Remounting filesystem..."
+sudo mount -t simplefs -o loop $IMAGE test || { echo "mount failed"; exit 1; }
+echo "Remount succeeds."
+pushd test >/dev/null || { echo "pushd failed"; exit 1; }
+
+# check if files exist and content is correct after remounting
+for ((i=1; i<=$MOUNT_TEST; i++))
+do
+    if [[ -f "file_$i.txt" ]]; then
+        content=$(cat "file_$i.txt" | tr -d '\000')
+        if [[ "$content" == "file_$i" ]]; then
+            echo "Success: file_$i.txt content is correct."
+        else
+            echo "Failed: file_$i.txt content is incorrect."
+            exit 1
+        fi
+    else
+        echo "Failed: file_$i.txt does not exist."
+        exit 1
+    fi
+done
+find . -name 'file_[0-9]*.txt' | xargs sudo rm || { echo "Failed to delete files"; exit 1; }
 
 # hard link
 test_op 'ln file hdlink'
@@ -96,4 +133,4 @@ check_exist $S_MOD 1 symlink
 sleep 1
 popd >/dev/null
 sudo umount test
-sudo rmmod simplefs
+sudo rmmod simplefs