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(This is the same problem reported against syslog-ng in Gentoo at
https://bugs.gentoo.org/show_bug.cgi?id=154465 -- this contains
a patch which fixes the problem with a similar approach to that
taken in sysklogd.)

When syslog-ng writes to a tty under Linux, for example as a
result of a usertty directive, the write syscall to
/dev/ttyN can ocassionally block indefinitely.  One
situation when this occurs is when the user has set XOFF
(perhaps with Ctrl-S or Scroll Lock).

Aside from the fact that this obvious prevents any further
log messages from being written, /dev/log's buffer
eventually fills up causing other programs to block writing
to /dev/log.  In extremis, this can render a machine
inaccesible when ssh, etc., all block preventing access.


Reproducible: Always

Steps to Reproduce:

1. Check that there is a usertty("*") directive for (say) kern.emerg logs
2. Ensure syslog-ng is running
3. On console, press Scroll Lock
4. Log something, e.g. logger -p kern.emerg 'Foo'.
5. Repeat #4 many times; eventually it will hang trying to log


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