[syslinux] lpxelinux.0 with device that doesn't support Interrupts

[Gene Cumm]

On Fri, Feb 26, 2016 at 6:10 PM, Wissam Shoukair via Syslinux
<syslinux at zytor.com> wrote:
> I am experiencing an issue where I ran ipxe (as an option rom) and downloaded the lpxelinux.0 as the bootloader.
> Next it should download the ldlinux.c32 file using UNDI API.
> but before that it will close and open  the underlying device (which is ipxe), and hooking the device interrupt so it can start getting some packets.

Why load lpxelinux.0?  iPXE is normally configured to support HTTP and
PXELINUX supports calling iPXE for HTTP access.  PXELINUX's callback
was broken at one point but is functioning in the latest git code and
will be in 6.04.

> What I'm experiencing is that if the underlying device doesn't support interrupts, i.e. the IntNumber that is returned in PXENV_UNDI_GET_INFORMATION is 0, then lpxelinux.0 will hook IRQ0 which is very bad behavior.
>
> one good example of the faulty code is in undinet.c where we open a device, we hook the IRQ regardless if its 0 or not, while in the latest iPXE code this behavior was corrected and a check expression was added to avoid such bad behavior

It helps to give context.  I'd have to assume this is iPXE's
src/arch/i386/drivers/net/undinet.c but project, path, line, and
function are helpful.

See core/fs/pxe/isr.c:243 pxe_start_isr(), lpxelinux.0 does NOT hook
IRQ 0 and falls back to polling mode.  This code hasn't changed since
the 4.10-pre* series.

-- 
-Gene

> -----Original Message-----
> From: Syslinux [mailto:syslinux-bounces at zytor.com] On Behalf Of Geert Stappers via Syslinux
> Sent: Friday, February 26, 2016 15:35
> To: syslinux at zytor.com
> Subject: Re: [syslinux] lpxelinux.0 with device that doesn't support Interrupts
>
> On Fri, Feb 26, 2016 at 01:00:21PM +0000, Wissam Shoukair via Syslinux wrote:
>> hi
>> does anyone know if there are some known issues with running
>> lpxelinux.0 with device that doesn't support Interrupts?
>> i.e. irq function is null...
>
> Take some time to elaborate the question.