Forwarding unwritable FD hangs
- Found in: 1.18
CategoryFixed. Fixed in: 675 for release 1.19
Normally, redirecting stdout to an unwritable FD prints an error:
$ /bin/echo hello 1</dev/null /bin/echo: write error: Bad file descriptor
Although the shell's builtin "echo" command does not print the error:
$ echo hello 1</dev/null
Forwarding this FD using pola-run results in a traceback being printed on PlashRelease1.18 and pola-run then hangs:
$ pola-run -fw / -e echo hello 1</dev/null
Traceback (most recent call last):
File "/var/lib/python-support/python2.4/plash/filedesc.py", line 95, in _write_callback
written_count = os.write(self._dest_fd, self._buf)
OSError: [Errno 9] Bad file descriptor
Traceback (most recent call last):
File "/var/lib/python-support/python2.4/plash/pola_run_args.py", line 310, in callback
forwarder.flush()
File "/var/lib/python-support/python2.4/plash/filedesc.py", line 118, in flush
written = os.write(self._dest_fd, self._buf)
OSError: [Errno 9] Bad file descriptor
<hangs...>
SSH handles this correctly:
$ ssh localhost echo hello 1</dev/null
In later versions, with PlashIssues/StdoutGetsTruncated fixed, the traceback is not printed but pola-run still hangs. The cause is that poll() never returns POLLIN or POLLOUT for unreadable and unwritable FDs respectively.
This was found by Thomas Leonard: see http://lists.gnu.org/archive/html/plash/2007-12/msg00000.html
See EventLoopAndFDs for general implementation notes in this area.