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.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

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;
 };

fs/erofs/internal.h

@@ -266,7 +266,6 @@ struct erofs_inode {
 			unsigned short z_advise;
 			unsigned char  z_algorithmtype[2];
 			unsigned char  z_logical_clusterbits;
-			unsigned char  z_physical_clusterbits[2];
 		};
 #endif	/* CONFIG_EROFS_FS_ZIP */
 	};

fs/erofs/zdata.c

@@ -430,8 +430,7 @@ static int z_erofs_register_collection(struct z_erofs_collector *clt,
 	else
 		pcl->algorithmformat = Z_EROFS_COMPRESSION_SHIFTED;
 
-	pcl->clusterbits = EROFS_I(inode)->z_physical_clusterbits[0];
-	pcl->clusterbits -= PAGE_SHIFT;
+	pcl->clusterbits = 0;
 
 	/* new pclusters should be claimed as type 1, primary and followed */
 	pcl->next = clt->owned_head;

fs/erofs/zmap.c

@@ -17,11 +17,8 @@ int z_erofs_fill_inode(struct inode *inode)
 		vi->z_algorithmtype[0] = 0;
 		vi->z_algorithmtype[1] = 0;
 		vi->z_logical_clusterbits = LOG_BLOCK_SIZE;
-		vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits;
-		vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits;
 		set_bit(EROFS_I_Z_INITED_BIT, &vi->flags);
 	}
-
 	inode->i_mapping->a_ops = &z_erofs_aops;
 	return 0;
 }
@@ -77,18 +74,6 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 	}
 
 	vi->z_logical_clusterbits = LOG_BLOCK_SIZE + (h->h_clusterbits & 7);
-	vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits +
-					((h->h_clusterbits >> 3) & 3);
-
-	if (vi->z_physical_clusterbits[0] != LOG_BLOCK_SIZE) {
-		erofs_err(sb, "unsupported physical clusterbits %u for nid %llu, please upgrade kernel",
-			  vi->z_physical_clusterbits[0], vi->nid);
-		err = -EOPNOTSUPP;
-		goto unmap_done;
-	}
-
-	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
-					((h->h_clusterbits >> 5) & 7);
 	/* paired with smp_mb() at the beginning of the function */
 	smp_mb();
 	set_bit(EROFS_I_Z_INITED_BIT, &vi->flags);