erofs: use meta buffers for reading directories

Previously, directory inodes are directly handled with page cache
interfaces.

In order to support sub-page directory blocks and folios, let's
convert them into the latest metabuf infrastructure as well and
this patch addresses the readdir case first.

Link: https://lore.kernel.org/r/20220316012246.95131-1-hsiangkao@linux.alibaba.comReviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/data.c

@@ -28,10 +28,10 @@ void erofs_put_metabuf(struct erofs_buf *buf)
 	buf->page = NULL;
 }
 
-void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
-			erofs_blk_t blkaddr, enum erofs_kmap_type type)
+void *erofs_bread(struct erofs_buf *buf, struct inode *inode,
+		  erofs_blk_t blkaddr, enum erofs_kmap_type type)
 {
-	struct address_space *const mapping = sb->s_bdev->bd_inode->i_mapping;
+	struct address_space *const mapping = inode->i_mapping;
 	erofs_off_t offset = blknr_to_addr(blkaddr);
 	pgoff_t index = offset >> PAGE_SHIFT;
 	struct page *page = buf->page;
@@ -60,6 +60,12 @@ void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
 	return buf->base + (offset & ~PAGE_MASK);
 }
 
+void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
+			 erofs_blk_t blkaddr, enum erofs_kmap_type type)
+{
+	return erofs_bread(buf, sb->s_bdev->bd_inode, blkaddr, type);
+}
+
 static int erofs_map_blocks_flatmode(struct inode *inode,
 				     struct erofs_map_blocks *map,
 				     int flags)

fs/erofs/dir.c

@@ -2,6 +2,7 @@
 /*
  * Copyright (C) 2017-2018 HUAWEI, Inc.
  *             https://www.huawei.com/
+ * Copyright (C) 2022, Alibaba Cloud
  */
 #include "internal.h"
 
@@ -67,7 +68,7 @@ static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
 static int erofs_readdir(struct file *f, struct dir_context *ctx)
 {
 	struct inode *dir = file_inode(f);
-	struct address_space *mapping = dir->i_mapping;
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
 	const size_t dirsize = i_size_read(dir);
 	unsigned int i = ctx->pos / EROFS_BLKSIZ;
 	unsigned int ofs = ctx->pos % EROFS_BLKSIZ;
@@ -75,26 +76,19 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
 	bool initial = true;
 
 	while (ctx->pos < dirsize) {
-		struct page *dentry_page;
 		struct erofs_dirent *de;
 		unsigned int nameoff, maxsize;
 
-		dentry_page = read_mapping_page(mapping, i, NULL);
-		if (dentry_page == ERR_PTR(-ENOMEM)) {
-			err = -ENOMEM;
-			break;
-		} else if (IS_ERR(dentry_page)) {
+		de = erofs_bread(&buf, dir, i, EROFS_KMAP);
+		if (IS_ERR(de)) {
 			erofs_err(dir->i_sb,
 				  "fail to readdir of logical block %u of nid %llu",
 				  i, EROFS_I(dir)->nid);
-			err = -EFSCORRUPTED;
+			err = PTR_ERR(de);
 			break;
 		}
 
-		de = (struct erofs_dirent *)kmap(dentry_page);
-
 		nameoff = le16_to_cpu(de->nameoff);
-
 		if (nameoff < sizeof(struct erofs_dirent) ||
 		    nameoff >= PAGE_SIZE) {
 			erofs_err(dir->i_sb,
@@ -119,10 +113,6 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
 		err = erofs_fill_dentries(dir, ctx, de, &ofs,
 					  nameoff, maxsize);
 skip_this:
-		kunmap(dentry_page);
-
-		put_page(dentry_page);
-
 		ctx->pos = blknr_to_addr(i) + ofs;
 
 		if (err)
@@ -130,6 +120,7 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
 		++i;
 		ofs = 0;
 	}
+	erofs_put_metabuf(&buf);
 	return err < 0 ? err : 0;
 }
 

fs/erofs/internal.h

@@ -479,6 +479,8 @@ struct erofs_map_dev {
 extern const struct file_operations erofs_file_fops;
 void erofs_unmap_metabuf(struct erofs_buf *buf);
 void erofs_put_metabuf(struct erofs_buf *buf);
+void *erofs_bread(struct erofs_buf *buf, struct inode *inode,
+		  erofs_blk_t blkaddr, enum erofs_kmap_type type);
 void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
 			 erofs_blk_t blkaddr, enum erofs_kmap_type type);
 int erofs_map_dev(struct super_block *sb, struct erofs_map_dev *dev);