erofs: support on-disk compressed fragments data

Introduce on-disk compressed fragments data feature.

This approach adds a new field called `h_fragmentoff' in the per-file
compression header to indicate the fragment offset of each tail pcluster
or the whole file in the special packed inode.

Similar to ztailpacking, it will also find and record the 'headlcn'
of the tail pcluster when initializing per-inode zmap for making
follow-on requests more easy.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/YzHKxcFTlHGgXeH9@B-P7TQMD6M-0146.local
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

1 files changed, 49 insertions, 1 deletions

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5792ca9e0d5e..c92a72f5bca6 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -650,6 +650,35 @@ static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
 		la < fe->headoffset;
 }
 
+static int z_erofs_read_fragment(struct inode *inode, erofs_off_t pos,
+				 struct page *page, unsigned int pageofs,
+				 unsigned int len)
+{
+	struct inode *packed_inode = EROFS_I_SB(inode)->packed_inode;
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
+	u8 *src, *dst;
+	unsigned int i, cnt;
+
+	pos += EROFS_I(inode)->z_fragmentoff;
+	for (i = 0; i < len; i += cnt) {
+		cnt = min_t(unsigned int, len - i,
+			    EROFS_BLKSIZ - erofs_blkoff(pos));
+		src = erofs_bread(&buf, packed_inode,
+				  erofs_blknr(pos), EROFS_KMAP);
+		if (IS_ERR(src)) {
+			erofs_put_metabuf(&buf);
+			return PTR_ERR(src);
+		}
+
+		dst = kmap_local_page(page);
+		memcpy(dst + pageofs + i, src + erofs_blkoff(pos), cnt);
+		kunmap_local(dst);
+		pos += cnt;
+	}
+	erofs_put_metabuf(&buf);
+	return 0;
+}
+
 static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 				struct page *page, struct page **pagepool)
 {
@@ -688,7 +717,8 @@ repeat:
 		/* didn't get a valid pcluster previously (very rare) */
 	}
 
-	if (!(map->m_flags & EROFS_MAP_MAPPED))
+	if (!(map->m_flags & EROFS_MAP_MAPPED) ||
+	    map->m_flags & EROFS_MAP_FRAGMENT)
 		goto hitted;
 
 	err = z_erofs_collector_begin(fe);
@@ -735,6 +765,24 @@ hitted:
 		zero_user_segment(page, cur, end);
 		goto next_part;
 	}
+	if (map->m_flags & EROFS_MAP_FRAGMENT) {
+		unsigned int pageofs, skip, len;
+
+		if (offset > map->m_la) {
+			pageofs = 0;
+			skip = offset - map->m_la;
+		} else {
+			pageofs = map->m_la & ~PAGE_MASK;
+			skip = 0;
+		}
+		len = min_t(unsigned int, map->m_llen - skip, end - cur);
+		err = z_erofs_read_fragment(inode, skip, page, pageofs, len);
+		if (err)
+			goto out;
+		++spiltted;
+		tight = false;
+		goto next_part;
+	}
 
 	exclusive = (!cur && (!spiltted || tight));
 	if (cur)