[syslinux] Getting HTTP path-prefix to work with syslinux.efi

[Alexander Perlis]

For those who use pxelinux-options to modify your (l)pxelinux.0 or your 
syslinux.efi and are having trouble with HTTP, see below...


Regarding the "-a" and "-b" options, with (l)pxelinux.0 I discovered at 
some point in the past, after some trials, that the following 
combination worked great for me:

   -b next-server   my.ip.address
   -a path-prefix   http://my.ip.address/
   -a config-file   pxe.bios.cfg

Thus, with syslinux.efi I similarly tried:

  -b next-server my.ip.address
  -a path-prefix http://my.ip.address/
  -a config-file pxe.efi64.cfg

But now, after the initial TFTP transfer of syslinux.efi, the client 
would hang (with no attempt to speak on the network).

If I instead removed the "-a path-prefix" line, then syslinux.efi would 
correctly load my configuration, but of course all file transfers are 
using the slower TFTP.

On a whim, I then tried "-b path-prefix" instead of "-a path-prefix", 
and that was the solution! Everything works! Using "-b path-prefix" also 
works on legacy BIOS.

In summary, the following works for me both on legacy BIOS and EFI:

  -b next-server my.ip.address
  -b path-prefix http://my.ip.address/
  -a config-file pxe.ARCH.cfg


Developers: whereas with legacy BIOS both "-a path-prefix" and "-b 
path-prefix" work, yet on syslinux.efi it seems "-a path-prefix" causes 
corrupt behavior (value is neither ignored nor used correctly), this 
seems like a bug. If a developer on this list would like to have me run 
other tests for you on my hardware, I'm happy to oblige.

Thanks,
Alex