[gPXE] Setting delay time to boot

[Miller, Shao]

Good day Jon,

In regards to a gPXE 'waitfor <ip> <port> <timeout>' command, I have a
few thoughts:

If gPXE were to someday support IPv6 or some other network protocol,
would this command be as applicable/relevant?

It would seem that the <port> option implies that we have some way of
knowing that the <port> is available.  Would it make sense to tie <port>
to something that gPXE knows how to use, such as a download protocol or
SAN-boot protocol?

Given that gPXE has a strong focus on small code size for ROM build
targets, could 'waitfor' or other similar use cases be better
implemented in a more generic fashion?

If the check can be accomplished by repeated download attempts in a
loop, the scripting discussion in the gPXE developers' mailing-list
could potentially come to fruition and accomplish this same behaviour in
a more programmatically generic way, with 'if' and loops, for example.

As it stands, there are patches not yet committed to the gPXE official
code-base which can accomplish the behaviour of the suggested 'waitfor'
command, if the assumption is that a download trial is roughly the same
as testing for <port>.

#!gpxe
clear script_errors
dhcp net0
: test_download
chain http://ip:8080/some_boot_file
sleep 10
goto test_download

In the above, 'chain' should not return, but if it does, we wait ten
seconds and retry.  The above does not work in current gPXE, but does
work with some of the patches under discussion.

- Shao Miller