erofs: reserve physical_clusterbits[]

Formal big pcluster design is actually more powerful / flexable than
the previous thought whose pclustersize was fixed as power-of-2 blocks,
which was obviously inefficient and space-wasting. Instead, pclustersize
can now be set independently for each pcluster, so various pcluster
sizes can also be used together in one file if mkfs wants (for example,
according to data type and/or compression ratio).

Let's get rid of previous physical_clusterbits[] setting (also notice
that corresponding on-disk fields are still 0 for now). Therefore,
head1/2 can be used for at most 2 different algorithms in one file and
again pclustersize is now independent of these.

Link: https://lore.kernel.org/r/20210407043927.10623-2-xiang@kernel.org
Acked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
index 17bc0b5f117d..626b7d3e9ab7 100644
--- a/fs/erofs/erofs_fs.h
+++ b/fs/erofs/erofs_fs.h
@@ -233,9 +233,7 @@ struct z_erofs_map_header {
 	__u8	h_algorithmtype;
 	/*
 	 * bit 0-2 : logical cluster bits - 12, e.g. 0 for 4096;
-	 * bit 3-4 : (physical - logical) cluster bits of head 1:
-	 *       For example, if logical clustersize = 4096, 1 for 8192.
-	 * bit 5-7 : (physical - logical) cluster bits of head 2.
+	 * bit 3-7 : reserved.
 	 */
 	__u8	h_clusterbits;
 };