erofs: move preparation logic into z_erofs_pcluster_begin()

Some preparation logic should be part of z_erofs_pcluster_begin()
instead of z_erofs_do_read_page().  Let's move now.
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230817082813.81180-3-hsiangkao@linux.alibaba.com

fs/erofs/zdata.c

@@ -852,6 +852,8 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
 static int z_erofs_pcluster_begin(struct z_erofs_decompress_frontend *fe)
 {
 	struct erofs_map_blocks *map = &fe->map;
+	struct super_block *sb = fe->inode->i_sb;
+	erofs_blk_t blknr = erofs_blknr(sb, map->m_pa);
 	struct erofs_workgroup *grp = NULL;
 	int ret;
 
@@ -861,8 +863,7 @@ static int z_erofs_pcluster_begin(struct z_erofs_decompress_frontend *fe)
 	DBG_BUGON(fe->owned_head == Z_EROFS_PCLUSTER_NIL);
 
 	if (!(map->m_flags & EROFS_MAP_META)) {
-		grp = erofs_find_workgroup(fe->inode->i_sb,
-					   map->m_pa >> PAGE_SHIFT);
+		grp = erofs_find_workgroup(sb, blknr);
 	} else if ((map->m_pa & ~PAGE_MASK) + map->m_plen > PAGE_SIZE) {
 		DBG_BUGON(1);
 		return -EFSCORRUPTED;
@@ -881,9 +882,26 @@ static int z_erofs_pcluster_begin(struct z_erofs_decompress_frontend *fe)
 	} else if (ret) {
 		return ret;
 	}
+
 	z_erofs_bvec_iter_begin(&fe->biter, &fe->pcl->bvset,
 				Z_EROFS_INLINE_BVECS, fe->pcl->vcnt);
-	/* since file-backed online pages are traversed in reverse order */
+	if (!z_erofs_is_inline_pcluster(fe->pcl)) {
+		/* bind cache first when cached decompression is preferred */
+		z_erofs_bind_cache(fe);
+	} else {
+		void *mptr;
+
+		mptr = erofs_read_metabuf(&map->buf, sb, blknr, EROFS_NO_KMAP);
+		if (IS_ERR(mptr)) {
+			ret = PTR_ERR(mptr);
+			erofs_err(sb, "failed to get inline data %d", ret);
+			return ret;
+		}
+		get_page(map->buf.page);
+		WRITE_ONCE(fe->pcl->compressed_bvecs[0].page, map->buf.page);
+		fe->mode = Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE;
+	}
+	/* file-backed inplace I/O pages are traversed in reverse order */
 	fe->icur = z_erofs_pclusterpages(fe->pcl);
 	return 0;
 }
@@ -982,39 +1000,15 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 		err = z_erofs_map_blocks_iter(inode, map, 0);
 		if (err)
 			goto out;
-	} else {
-		if (fe->pcl)
-			goto hitted;
-		/* didn't get a valid pcluster previously (very rare) */
-	}
-
-	if (!(map->m_flags & EROFS_MAP_MAPPED) ||
-	    map->m_flags & EROFS_MAP_FRAGMENT)
+	} else if (fe->pcl) {
 		goto hitted;
+	}
 
-	err = z_erofs_pcluster_begin(fe);
-	if (err)
-		goto out;
-
-	if (z_erofs_is_inline_pcluster(fe->pcl)) {
-		void *mp;
-
-		mp = erofs_read_metabuf(&fe->map.buf, inode->i_sb,
-					erofs_blknr(inode->i_sb, map->m_pa),
-					EROFS_NO_KMAP);
-		if (IS_ERR(mp)) {
-			err = PTR_ERR(mp);
-			erofs_err(inode->i_sb,
-				  "failed to get inline page, err %d", err);
+	if ((map->m_flags & EROFS_MAP_MAPPED) &&
+	    !(map->m_flags & EROFS_MAP_FRAGMENT)) {
+		err = z_erofs_pcluster_begin(fe);
+		if (err)
 			goto out;
-		}
-		get_page(fe->map.buf.page);
-		WRITE_ONCE(fe->pcl->compressed_bvecs[0].page,
-			   fe->map.buf.page);
-		fe->mode = Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE;
-	} else {
-		/* bind cache first when cached decompression is preferred */
-		z_erofs_bind_cache(fe);
 	}
 hitted:
 	/*