debugfs: document zap_block & dump_block

index 520933a..9a05ef7 100644
@@ -181,10 +181,10 @@ request do_set_mmp_value, "Set MMP value",
 request do_extent_open, "Open inode for extent manipulation",
 	extent_open, eo;
 
-request do_zap_block, "Zap block",
+request do_zap_block, "Zap block: fill with 0, pattern, flip bits etc.",
 	zap_block, zap;
 
-request do_dump_block, "Zap block",
+request do_dump_block, "Dump contents of a block",
 	block_dump, bp;
 
 end;

index bfcb1a8..4164c3a 100644
@@ -215,6 +215,10 @@ option is given set the owner, group and permissions information on
 to match 
 .IR filespec .
 .TP
+.I dump_block [-f out_file] block_num
+Dump the contents of a block, optionally to
+.IR out_file .
+.TP
 .I dump_mmp
 Display the multiple-mount protection (mmp) field values.
 .TP

@@ -612,6 +616,14 @@ Create a file in the filesystem named
 and copy the contents of
 .I source_file
 into the destination file.
+.TP
+.I zap_block [-f file] [-o offset] [-l length] [-p pattern] block_num
+Zero, or pattern-fill, portions of a block within a file or
+within the filesystem.
+.TP
+.I zap_block [-f file] [-b bit] block_num
+Bit-flip portions of a block within a file or
+within the filesystem.
 .SH ENVIRONMENT VARIABLES
 .TP
 .B DEBUGFS_PAGER, PAGER