[PATCH v3 04/12] ftrfs: add directory operations

[Aurelien DESBRIERES <aurelien@hackers.camp>]

Implement directory iteration and lookup:

- ftrfs_readdir(): iterate directory entries from direct blocks,
  emit via dir_emit_dots() then dir_emit() for real entries,
  use ctx->pos as entry index with INT_MAX as EOF sentinel
- ftrfs_lookup(): search directory blocks for a matching name,
  call ftrfs_iget() on match and return via d_splice_alias()

Both functions scan ftrfs_dir_entry records in direct block
pointers only (no indirect block support yet).

Signed-off-by: Aurelien DESBRIERES <aurelien@hackers.camp>
---
 fs/ftrfs/dir.c | 132 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 fs/ftrfs/dir.c

diff --git a/fs/ftrfs/dir.c b/fs/ftrfs/dir.c
new file mode 100644
index 000000000000..dbf0102a40f3
--- /dev/null
+++ b/fs/ftrfs/dir.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * FTRFS — Directory operations
+ * Author: roastercode - Aurelien DESBRIERES <aurelien@hackers.camp>
+ */
+
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include "ftrfs.h"
+
+/*
+ * ftrfs_readdir — iterate directory entries
+ */
+static int ftrfs_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct inode       *inode = file_inode(file);
+	struct super_block *sb    = inode->i_sb;
+	struct ftrfs_inode_info *fi = FTRFS_I(inode);
+	struct buffer_head *bh;
+	struct ftrfs_dir_entry *de;
+	unsigned long block_idx, block_no;
+	unsigned int  offset;
+
+	/* EOF guard */
+	if (ctx->pos == INT_MAX)
+		return 0;
+	/* Emit . and .. (ctx->pos: 0=., 1=.., 2+=real entries) */
+	if (ctx->pos < 2) {
+		if (!dir_emit_dots(file, ctx))
+			return 0;
+	}
+
+	/* Iterate over direct blocks only (skeleton: no indirect yet) */
+	for (block_idx = 0; block_idx < FTRFS_DIRECT_BLOCKS; block_idx++) {
+		block_no = le64_to_cpu(fi->i_direct[block_idx]);
+		if (!block_no)
+			break;
+
+		bh = sb_bread(sb, block_no);
+		if (!bh)
+			continue;
+
+		offset = 0;
+		while (offset < FTRFS_BLOCK_SIZE) {
+			de = (struct ftrfs_dir_entry *)(bh->b_data + offset);
+
+			if (!de->d_rec_len)
+				break; /* end of dir block */
+
+			if (de->d_ino && de->d_name_len) {
+				if (!dir_emit(ctx,
+					      de->d_name,
+					      de->d_name_len,
+					      le64_to_cpu(de->d_ino),
+					      de->d_file_type)) {
+					brelse(bh);
+					return 0;
+				}
+				ctx->pos++;
+			}
+
+			offset += le16_to_cpu(de->d_rec_len);
+		}
+
+		brelse(bh);
+	}
+
+	ctx->pos = INT_MAX;
+	return 0;
+}
+
+/*
+ * ftrfs_lookup — find dentry in directory
+ */
+struct dentry *ftrfs_lookup(struct inode *dir,
+				   struct dentry *dentry,
+				   unsigned int flags)
+{
+	struct super_block      *sb = dir->i_sb;
+	struct ftrfs_inode_info *fi = FTRFS_I(dir);
+	struct buffer_head      *bh;
+	struct ftrfs_dir_entry  *de;
+	struct inode            *inode = NULL;
+	unsigned long            block_idx, block_no;
+	unsigned int             offset;
+
+	if (dentry->d_name.len > FTRFS_MAX_FILENAME)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	for (block_idx = 0; block_idx < FTRFS_DIRECT_BLOCKS; block_idx++) {
+		block_no = le64_to_cpu(fi->i_direct[block_idx]);
+		if (!block_no)
+			break;
+
+		bh = sb_bread(sb, block_no);
+		if (!bh)
+			continue;
+
+		offset = 0;
+		while (offset < FTRFS_BLOCK_SIZE) {
+			de = (struct ftrfs_dir_entry *)(bh->b_data + offset);
+
+			if (!de->d_rec_len)
+				break; /* end of dir block */
+
+			if (de->d_ino &&
+			    de->d_name_len == dentry->d_name.len &&
+			    !memcmp(de->d_name, dentry->d_name.name,
+				    de->d_name_len)) {
+				unsigned long ino = le64_to_cpu(de->d_ino);
+
+				brelse(bh);
+				inode = ftrfs_iget(sb, ino);
+				goto found;
+			}
+
+			offset += le16_to_cpu(de->d_rec_len);
+		}
+		brelse(bh);
+	}
+
+found:
+	return d_splice_alias(inode, dentry);
+}
+
+const struct file_operations ftrfs_dir_operations = {
+	.llseek  = generic_file_llseek,
+	.read    = generic_read_dir,
+	.iterate_shared = ftrfs_readdir,
+};
+
+
-- 
2.52.0