[syslinux] pxelinux implementation questions
H. Peter Anvin
hpa at zytor.com
Fri Jun 20 11:55:47 PDT 2003
Alexander Sack wrote:
> Hi,
>
> I've been looking at the pxelinux code and I was wondering a couple of
> things:
>
> 1) Why does pxelinux create UDP packets from scratch instead of use the
> Intel PXE TFTP OPEN/CLOSE/READ calls? I'm assuming this is to support
> TFTP options like tsize right? Did earlier versions of pxelinux use the
> TFTP calls directly?
>
Because they're largely useless. They have too many limitations -- only
one transaction at one time, must go into contiguous memory, and they
will write to the screen and read from the keyboard (there are ways
you're *supposed* to be able to override that, but they frequently don't
work.)
> 2) How big of an image can pxelinux download (minus memory constraints)?
> My understanding is that tftp packet numbers are from 0-65535 yielding a
> maximum size of 32MB. Yet, from the revision history, it seems pxelinux
> can handle bigger images? (I don't see any wrap around handling though
> I maybe not looking hard enough in seachdir() - from the looks of it,
> the only way I can see pxelinux downloading a bigger image is if the
> tftp_blksize is negotiated greater than 512, right?)
Nope. After FFFF follows 0000.
> 3) Why does pxelinux require tsize? Does it make a difference what
> size the file is as long as the last packet returns < 512?
PXELINUX wants to know the size of the file before it downloads it.
-hpa
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