[PATCH v3 2/3] erofs-utils: add erofs_read_metadata() helper

[Jingbo Xu]

Add erofs_read_metadata() helper reading variable-sized metadata from
inode specified by @nid.  Read from meta inode if @nid is 0.

Signed-off-by: Jingbo Xu <jefflexu at linux.alibaba.com>
---
 include/erofs/internal.h |  2 +
 lib/data.c               | 84 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)

diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index a04e6a6..3e7319d 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -364,6 +364,8 @@ int erofs_read_one_data(struct erofs_inode *inode, struct erofs_map_blocks *map,
 int z_erofs_read_one_data(struct erofs_inode *inode,
 			struct erofs_map_blocks *map, char *raw, char *buffer,
 			erofs_off_t skip, erofs_off_t length, bool trimmed);
+void *erofs_read_metadata(struct erofs_sb_info *sbi, erofs_nid_t nid,
+			  erofs_off_t *offset, int *lengthp);
 
 static inline int erofs_get_occupied_size(const struct erofs_inode *inode,
 					  erofs_off_t *size)
diff --git a/lib/data.c b/lib/data.c
index a172bb5..662e922 100644
--- a/lib/data.c
+++ b/lib/data.c
@@ -372,3 +372,87 @@ int erofs_pread(struct erofs_inode *inode, char *buf,
 	}
 	return -EINVAL;
 }
+
+static void *erofs_read_metadata_nid(struct erofs_sb_info *sbi, erofs_nid_t nid,
+				     erofs_off_t *offset, int *lengthp)
+{
+	struct erofs_inode vi = { .sbi = sbi, .nid = nid };
+	__le16 __len;
+	int ret, len;
+	char *buffer;
+
+	ret = erofs_read_inode_from_disk(&vi);
+	if (ret)
+		return ERR_PTR(ret);
+
+	*offset = round_up(*offset, 4);
+	ret = erofs_pread(&vi, (void *)&__len, sizeof(__le16), *offset);
+	if (ret)
+		return ERR_PTR(ret);
+
+	len = le16_to_cpu(__len);
+	if (!len)
+		return ERR_PTR(-EFSCORRUPTED);
+
+	buffer = malloc(len);
+	if (!buffer)
+		return ERR_PTR(-ENOMEM);
+	*offset += sizeof(__le16);
+	*lengthp = len;
+
+	ret = erofs_pread(&vi, buffer, len, *offset);
+	if (ret) {
+		free(buffer);
+		return ERR_PTR(ret);
+	}
+	*offset += len;
+	return buffer;
+}
+
+static void *erofs_read_metadata_bdi(struct erofs_sb_info *sbi,
+				     erofs_off_t *offset, int *lengthp)
+{
+	int ret, len, i, cnt;
+	void *buffer;
+	u8 data[EROFS_MAX_BLOCK_SIZE];
+
+	*offset = round_up(*offset, 4);
+	ret = blk_read(sbi, 0, data, erofs_blknr(sbi, *offset), 1);
+	if (ret)
+		return ERR_PTR(ret);
+	len = le16_to_cpu(*(__le16 *)&data[erofs_blkoff(sbi, *offset)]);
+	if (!len)
+		return ERR_PTR(-EFSCORRUPTED);
+
+	buffer = malloc(len);
+	if (!buffer)
+		return ERR_PTR(-ENOMEM);
+	*offset += sizeof(__le16);
+	*lengthp = len;
+
+	for (i = 0; i < len; i += cnt) {
+		cnt = min_t(int, erofs_blksiz(sbi) - erofs_blkoff(sbi, *offset),
+			    len - i);
+		ret = blk_read(sbi, 0, data, erofs_blknr(sbi, *offset), 1);
+		if (ret) {
+			free(buffer);
+			return ERR_PTR(ret);
+		}
+		memcpy(buffer + i, data + erofs_blkoff(sbi, *offset), cnt);
+		*offset += cnt;
+	}
+	return buffer;
+}
+
+/*
+ * read variable-sized metadata, offset will be aligned by 4-byte
+ *
+ * @nid is 0 if metadata is in meta inode
+ */
+void *erofs_read_metadata(struct erofs_sb_info *sbi, erofs_nid_t nid,
+			  erofs_off_t *offset, int *lengthp)
+{
+	if (nid)
+		return erofs_read_metadata_nid(sbi, nid, offset, lengthp);
+	return erofs_read_metadata_bdi(sbi, offset, lengthp);
+}
-- 
2.19.1.6.gb485710b