Implement simplefs_file_open

file.c

@@ -245,6 +245,54 @@ static int simplefs_write_end(struct file *file,
     return ret;
 }
 
+/*
+ * Called when a file is opened in the simplefs.
+ * It checks the flags associated with the file opening mode (O_WRONLY, O_RDWR,
+ * O_TRUNC) and performs truncation if the file is being opened for write or
+ * read/write and the O_TRUNC flag is set.
+ *
+ * Truncation is achieved by reading the file's index block from disk, iterating
+ * over the data block pointers, releasing the associated data blocks, and
+ * updating the inode metadata (size and block count).
+ */
+static int simplefs_file_open(struct inode *inode, struct file *filp)
+{
+    bool wronly = (filp->f_flags & O_WRONLY);
+    bool rdwr = (filp->f_flags & O_RDWR);
+    bool trunc = (filp->f_flags & O_TRUNC);
+
+    if ((wronly || rdwr) && trunc && inode->i_size) {
+        struct buffer_head *bh_index;
+        struct simplefs_file_ei_block *ei_block;
+        sector_t iblock;
+
+        /* Fetch the file's extent block from disk */
+        bh_index = sb_bread(inode->i_sb, SIMPLEFS_INODE(inode)->ei_block);
+        if (!bh_index)
+            return -EIO;
+
+        ei_block = (struct simplefs_file_ei_block *) bh_index->b_data;
+
+        for (iblock = 0; iblock <= SIMPLEFS_MAX_EXTENTS &&
+                         ei_block->extents[iblock].ee_start;
+             iblock++) {
+            put_blocks(SIMPLEFS_SB(inode->i_sb),
+                       ei_block->extents[iblock].ee_start,
+                       ei_block->extents[iblock].ee_len);
+            memset(&ei_block->extents[iblock], 0,
+                   sizeof(struct simplefs_extent));
+        }
+        /* Update inode metadata */
+        inode->i_size = 0;
+        inode->i_blocks = 1;
+
+        mark_buffer_dirty(bh_index);
+        brelse(bh_index);
+        mark_inode_dirty(inode);
+    }
+    return 0;
+}
+
 const struct address_space_operations simplefs_aops = {
 #if SIMPLEFS_AT_LEAST(5, 19, 0)
     .readahead = simplefs_readahead,
@@ -262,4 +310,5 @@ const struct file_operations simplefs_file_ops = {
     .read_iter = generic_file_read_iter,
     .write_iter = generic_file_write_iter,
     .fsync = generic_file_fsync,
+    .open = simplefs_file_open,
 };