[PATCH v7 17/19] erofs: implement fscache-based data read for inline layout

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

Implement the data plane of reading data from data blobs over fscache
for inline layout.

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

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/fscache.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 65de1c754e80..d32cb5840c6d 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -60,6 +60,40 @@ static int erofs_fscache_meta_readpage(struct file *data, struct page *page)
 	return ret;
 }
 
+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.
+	 */
+	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_readpage(struct file *file, struct page *page)
 {
 	struct folio *folio = page_folio(page);
@@ -85,6 +119,12 @@ static int erofs_fscache_readpage(struct file *file, struct page *page)
 		goto out_uptodate;
 	}
 
+	/* inline readpage */
+	if (map.m_flags & EROFS_MAP_META) {
+		ret = erofs_fscache_readpage_inline(folio, &map);
+		goto out_uptodate;
+	}
+
 	/* no-inline readpage */
 	mdev = (struct erofs_map_dev) {
 		.m_deviceid = map.m_deviceid,
-- 
2.27.0