This lets you view the first n lines of output instead of the last n
lines, as though the output was piped through head.
This is how the standard watch command works, and can be more useful
when most of the information is at the top, such as in our dbg*.py
scripts (watch.py was originally used as a sort of inotifywait-esque
build runner, which is the main reason it's different).
To make this work, RingIO (renamed from LinesIO) now uses terminal
height as a part of its canvas rendering. This has the added benefit of
more rigorously enforcing the canvas boundaries, but risks breaking when
not associated with a terminal. But that raises the question, does
RingIO even make sense without a terminal?
Worst case you can bypass all of this with -z/--cat.
Since we were only registering our inotify reader after the previous
operation completed, it was easy to miss modifications that happened
faster than our scripts. Since our scripts are in Python, this happened
quite often and made it hard to trust the current state of scripts
with --keep-open, sort of defeating the purpose of --keep-open...
I think previously this race condition wasn't avoided because of the
potential to loop indefinitely if --keep-open referenced a file that the
script itself modified, but it's up to the user to avoid this if it is
an issue.
---
Also while fixing this, I noticed our use of the inotify_simple library
was leaking file descriptors everywhere! I just wasn't closing any
inotify objects at all. A bit concerning since scripts with --keep-open
can be quite long lived...
- 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.
