Some script tweaks around dbgrbyd.py

- Fixed off-by-one id for unknown tags.

- Allowed block_size and block to go unspecified, assumes the block
  device is one big block in that case.

- Added --buffer and --ignore-errors to watch.py, making it a bit better
  for watching slow and sometimes error scripts, such as dbgrbyd.py when
  watching a block device under test.

scripts/dbgrbyd.py

@@ -1,9 +1,10 @@
 #!/usr/bin/env python3
 
+import bisect
 import itertools as it
 import math as m
+import os
 import struct
-import bisect
 
 COLORS = [
     '34',   # blue
@@ -91,7 +92,7 @@ def tagrepr(tag, id, size, off=None):
                 if off is not None
                 else '-%d' % off)
     else:
-        return '0x%04x id%d %d' % (tag, id-1, size)
+        return '0x%04x id%d %d' % (tag, id, size)
 
 def show_log(block_size, data, rev, off, *,
         color=False,
@@ -527,7 +528,7 @@ def show_tree(block_size, data, rev, trunk, weight, *,
                         line))
 
 
-def main(disk, block_size, block1, block2=None, *,
+def main(disk, block_size=None, block1=0, block2=None, *,
         trunk=None,
         color='auto',
         **args):
@@ -539,9 +540,14 @@ def main(disk, block_size, block1, block2=None, *,
     else:
         color = False
 
+    with open(disk, 'rb') as f:
+        # if block_size is omitted, assume the block device is one big block
+        if block_size is None:
+            f.seek(0, os.SEEK_END)
+            block_size = f.tell()
+
         # read each block
         blocks = [block for block in [block1, block2] if block is not None]
-    with open(disk, 'rb') as f:
         datas = []
         for block in blocks:
             f.seek(block * block_size)
@@ -640,10 +646,12 @@ if __name__ == "__main__":
         help="File containing the block device.")
     parser.add_argument(
         'block_size',
+        nargs='?',
         type=lambda x: int(x, 0),
         help="Block size in bytes.")
     parser.add_argument(
         'block1',
+        nargs='?',
         type=lambda x: int(x, 0),
         help="Block address of the first metadata block.")
     parser.add_argument(

scripts/watch.py

@@ -140,6 +140,8 @@ def main(command, *,
         sleep=None,
         keep_open=False,
         keep_open_paths=None,
+        buffer=False,
+        ignore_errors=False,
         exit_on_error=False):
     returncode = 0
     try:
@@ -179,14 +181,19 @@ def main(command, *,
                         break
 
                     ring.write(line)
-                    if not cat:
+                    if not cat and not buffer and not ignore_errors:
                         ring.draw()
 
                 mpty.close()
                 proc.wait()
+
+                if ((buffer or ignore_errors)
+                        and not (ignore_errors and proc.returncode != 0)):
+                    ring.draw()
                 if exit_on_error and proc.returncode != 0:
                     returncode = proc.returncode
                     break
+
             except OSError as e:
                 if e.errno != errno.ETXTBSY:
                     raise
@@ -256,6 +263,14 @@ if __name__ == "__main__":
         dest='keep_open_paths',
         action='append',
         help="Use this path for inotify. Defaults to guessing.")
+    parser.add_argument(
+        '-b', '--buffer',
+        action='store_true',
+        help="Wait until command finishes to show the output.")
+    parser.add_argument(
+        '-i', '--ignore-errors',
+        action='store_true',
+        help="Only show output after successful runs. Implies --buffer.")
     parser.add_argument(
         '-e', '--exit-on-error',
         action='store_true',