migrate to linux 4.19, without ANY backward consideration

dir.c

 #include "khellofs.h"
 
-int hellofs_readdir(struct file *filp, void *dirent, filldir_t filldir) {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 11, 0)
+#error fs api changed in linux 3.11.0. Please use a better kernel to build my code!
+#endif
+
+int hellofs_iterate(struct file *filp, struct dir_context *ctx) {
     loff_t pos;
     struct inode *inode;
     struct super_block *sb;
@@ -9,8 +13,8 @@ int hellofs_readdir(struct file *filp, void *dirent, filldir_t filldir) {
     struct hellofs_dir_record *dir_record;
     uint64_t i;
 
-    pos = filp->f_pos;
-    inode = filp->f_dentry->d_inode;
+    pos = ctx->pos;
+    inode = filp->f_path.dentry->d_inode;
     sb = inode->i_sb;
     hellofs_inode = HELLOFS_INODE(inode);
 
@@ -25,7 +29,7 @@ int hellofs_readdir(struct file *filp, void *dirent, filldir_t filldir) {
         printk(KERN_ERR
                "Inode %llu of dentry %s is not a directory\n",
                hellofs_inode->inode_no,
-               filp->f_dentry->d_name.name);
+               filp->f_path.dentry->d_name.name);
         return -ENOTDIR;
     }
 
@@ -34,9 +38,8 @@ int hellofs_readdir(struct file *filp, void *dirent, filldir_t filldir) {
 
     dir_record = (struct hellofs_dir_record *)bh->b_data;
     for (i = 0; i < hellofs_inode->dir_children_count; i++) {
-        filldir(dirent, dir_record->filename, HELLOFS_FILENAME_MAXLEN, pos,
-                dir_record->inode_no, DT_UNKNOWN);
-        filp->f_pos += sizeof(struct hellofs_dir_record);
+        dir_emit(ctx, dir_record->filename, HELLOFS_FILENAME_MAXLEN, dir_record->inode_no, DT_UNKNOWN);
+        ctx->pos += sizeof(struct hellofs_dir_record);
         pos += sizeof(struct hellofs_dir_record);
         dir_record++;
     }

file.c

@@ -58,10 +58,11 @@ ssize_t hellofs_write(struct file *filp, const char __user *buf, size_t len,
     hellofs_inode = HELLOFS_INODE(inode);
     hellofs_sb = HELLOFS_SB(sb);
 
-    ret = generic_write_checks(filp, ppos, &len, 0);
-    if (ret) {
-        return ret;
-    }
+    // Recolic: compilation issue, temporary disable. TODO
+    // ret = generic_write_checks(filp, ppos, &len, 0);
+    // if (ret) {
+    //     return ret;
+    // }
 
     bh = sb_bread(sb, hellofs_inode->data_block_no);
     if (!bh) {

inode.c

 #include "khellofs.h"
+#include <linux/timekeeping.h>
 
 void hellofs_destroy_inode(struct inode *inode) {
     struct hellofs_inode *hellofs_inode = HELLOFS_INODE(inode);
@@ -17,7 +18,7 @@ void hellofs_fill_inode(struct super_block *sb, struct inode *inode,
     // TODO hope we can use hellofs_inode to store timespec
     inode->i_atime = inode->i_mtime 
                    = inode->i_ctime
-                   = CURRENT_TIME;
+                   = current_time(inode);
     inode->i_private = hellofs_inode;    
     
     if (S_ISDIR(hellofs_inode->mode)) {
@@ -296,4 +297,4 @@ struct dentry *hellofs_lookup(struct inode *dir,
            "No inode found for the filename: %s\n",
            child_dentry->d_name.name);
     return NULL;
-}
\ No newline at end of file
+}

khellofs.c

@@ -23,7 +23,7 @@ const struct inode_operations hellofs_inode_ops = {
 
 const struct file_operations hellofs_dir_operations = {
     .owner = THIS_MODULE,
-    .readdir = hellofs_readdir,
+    .iterate = hellofs_iterate,
 };
 
 const struct file_operations hellofs_file_operations = {

khellofs.h

@@ -41,7 +41,10 @@ struct dentry *hellofs_lookup(struct inode *parent_inode,
 int hellofs_mkdir(struct inode *dir, struct dentry *dentry,
                    umode_t mode);
 
-int hellofs_readdir(struct file *filp, void *dirent, filldir_t filldir);
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 11, 0)
+#error fs api changed in linux 3.11.0. Please use a better kernel to build my code!
+#endif
+int hellofs_iterate(struct file *filp, struct dir_context *ctx);
 
 ssize_t hellofs_read(struct file * filp, char __user * buf, size_t len,
                       loff_t * ppos);
@@ -107,4 +110,4 @@ int hellofs_alloc_data_block(struct super_block *sb, uint64_t *out_data_block_no
 int hellofs_create_inode(struct inode *dir, struct dentry *dentry,
                          umode_t mode);
 
-#endif /*__KHELLOFS_H__*/
\ No newline at end of file
+#endif /*__KHELLOFS_H__*/