[syslinux] PXERETRY directive

[Ady]

> On Thu, Apr 21, 2016 at 10:30 PM, Ady via Syslinux <syslinux at zytor.com> wrote:
> > Would someone please be so kind to explain / describe the PXERETRY
> > directive?
> 
> $ git grep -ni pxeretry
> com32/elflink/ldlinux/readconfig.c:1305:    else if (looking_at(p, "pxeretry"))
> com32/elflink/ldlinux/readconfig.c:1306:        PXERetry =
> atoi(skipspace(p + 8));
> 
> core/fs/pxe/pxe.c:275:    int i = PXERetry;
> 
> 
> It's used in pxe_searchdir() to affect how many times it retries to
> open a file and added in commit 4f989f247 for 4.03.
> 
> -- 
> -Gene
 
If possible, I would appreciate some additional information, perhaps 
aimed at common users?

Some of the following questions might sound strange to some readers, 
but I have found no information nor examples (nor experiences by 
others), at all, that could help describe the behavior for a common 
user.

Some of the questions that come to mind...

_ Does it affect the initial configuration file (e.g., 
"pxelinux.cfg/default")? At first sight, this question might seem to 
have no sense, considering that the configuration file needs to be 
found and be parsed first, before being able to act according to the 
PXERETRY directive in it. But, as a common user, I am not sure whether 
there could be some situation in which the / a configuration file is 
re-read and/or re-parsed -- the CONFIG directive, the INCLUDE 
directive, and the config.c32 module perhaps could be relevant for this 
question.

_ Does it affect every single file? For instance, if the user tries to 
execute a c32 module, does PXERETRY affect the command? And what about 
kernel / initrd file(s)? What happens when using pxechn.c32 or when 
loading a different network bootloader / NBP (for instance, with the 
PXE directive)?

_ Does it have any effect when using (vesa)menu.c32? Could it (perhaps 
unintentionally) affect the presentation of the boot menu itself (e.g. 
by loading the menu on screen several times, according to the PXERETRY 
value)?

_ Is the PXERETRY directive "sticky" (similarly to the SERIAL 
directive)? Can it be reset or changed by loading a different 
configuration file? Or perhaps, is it reset automatically after any 
particular situation / action / behavior?

_ Is there a valid range of values? Are non-decimal values accepted?

_ Would I be correct by assuming this is a global directive?

_ Is it valid for pxelinux.0 only? What about lpxelinux.0? What about 
syslinux.efi? Others?

_ Could someone please describe a usage case for this directive? Why 
might it be needed? What for? In which circumstances? Which behavior 
(or log's content) would trigger the need / desire for this directive? 
Which advantage or positive consequence(s) would it provide?


I wish I would have the means to actually test all these cases by 
myself, instead of asking here.

I hope these questions might also trigger the curiosity of others to 
test and report back, considering that this directive is not very 
well-known.

I also hope the potential replies / answers would help users to find 
this email thread as (initial) documentation for this PXERETRY 
directive, considering that it is not documented anywhere else (or at 
least, I couldn't find it).

TIA,
Ady.
 
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