[PATCH v6 18/22] erofs: implement fscache-based data read for inline layout

[Jeffle Xu <jefflexu@linux.alibaba.com>]

This patch implements the data plane of reading data from bootstrap blob
file over fscache for inline layout.

For the heading non-inline part, the data plane for non-inline layout is
resued, while only the tail packing part needs special handling.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/fscache.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 4a9a4e60c15d..d75958470645 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -74,8 +74,9 @@ static int erofs_fscache_readpage_noinline(struct folio *folio,
 {
 	struct fscache_cookie *cookie = map->m_fscache->cookie;
 	/*
-	 * 1) For FLAT_PLAIN layout, the output map.m_la shall be equal to o_la,
-	 * and the output map.m_pa is exactly the physical address of o_la.
+	 * 1) For FLAT_PLAIN and FLAT_INLINE (the heading non tail packing part)
+	 * layout, the output map.m_la shall be equal to o_la, and the output
+	 * map.m_pa is exactly the physical address of o_la.
 	 * 2) For CHUNK_BASED layout, the output map.m_la is rounded down to the
 	 * nearest chunk boundary, and the output map.m_pa is actually the
 	 * physical address of this chunk boundary. So we need to recalculate
@@ -86,6 +87,42 @@ static int erofs_fscache_readpage_noinline(struct folio *folio,
 	return erofs_fscache_read_folio(cookie, folio, start);
 }
 
+static int erofs_fscache_readpage_inline(struct folio *folio,
+					 struct erofs_map_blocks *map)
+{
+	struct inode *inode = folio_file_mapping(folio)->host;
+	struct super_block *sb = inode->i_sb;
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
+	erofs_blk_t blknr;
+	size_t offset, len;
+	void *src, *dst;
+
+	/*
+	 * For inline (tail packing) layout, the offset may be non-zero, which
+	 * can be calculated from corresponding physical address directly.
+	 * Currently only flat layout supports inline (FLAT_INLINE), and the
+	 * output map.m_pa is exactly the physical address of o_la in this case.
+	 */
+	offset = erofs_blkoff(map->m_pa);
+	blknr = erofs_blknr(map->m_pa);
+	len = map->m_llen;
+
+	src = erofs_read_metabuf(&buf, sb, blknr, EROFS_KMAP);
+	if (IS_ERR(src))
+		return PTR_ERR(src);
+
+	DBG_BUGON(folio_size(folio) != PAGE_SIZE);
+
+	dst = kmap(folio_page(folio, 0));
+	memcpy(dst, src + offset, len);
+	memset(dst + len, 0, PAGE_SIZE - len);
+	kunmap(folio_page(folio, 0));
+
+	erofs_put_metabuf(&buf);
+
+	return 0;
+}
+
 static int erofs_fscache_do_readpage(struct folio *folio)
 {
 	struct inode *inode = folio_file_mapping(folio)->host;
@@ -116,8 +153,12 @@ static int erofs_fscache_do_readpage(struct folio *folio)
 	if (ret)
 		return ret;
 
+	if (map.m_flags & EROFS_MAP_META)
+		return erofs_fscache_readpage_inline(folio, &map);
+
 	switch (vi->datalayout) {
 	case EROFS_INODE_FLAT_PLAIN:
+	case EROFS_INODE_FLAT_INLINE:
 	case EROFS_INODE_CHUNK_BASED:
 		return erofs_fscache_readpage_noinline(folio, &map);
 	default:
-- 
2.27.0