This is mac only (for now) and will not actually do anything until syslogd is
told to forward to /var/run/syslog.vsock.
syslog uses a SOCK_DGRAM connection to /var/run/syslog.vsock, however vsock
today is SOCK_STREAM only, so we need to "packetise" the stream. Do so by
writing the datagram length as a (little-endian) uint32 before the data itself.
This is slightly modelled after rfc6587 (syslog over TCP) but simplified by
using a 4-byte binary value rather than ASCII digits.
Arrange for vsudd to start before the logger so it is ready and waiting.
Note that the code in vsyslog.go needs to be rather careful about its own
logging, in particular logging forwarding failures over syslog seems likely to
make things worse. Instead this file logs to the console when errors occur,
this will be captured by the logging of the hyperkit VM console.
Signed-off-by: Ian Campbell <ian.campbell@docker.com>
