[syslinux] Syslinux fwrite support

Tal Lubko tallubko at yahoo.com
Sun May 22 17:31:34 PDT 2016



> -----Original Message-----
> From: Gene Cumm [mailto:gene.cumm at gmail.com]
> Sent: Saturday, May 21, 2016 4:44 PM
> To: Tal Lubko
> Cc: For discussion of Syslinux and tftp-hpa
> Subject: Re: [syslinux] Syslinux fwrite support
> 
> On Fri, May 20, 2016 at 11:14 PM, Tal Lubko <tallubko at yahoo.com> wrote:
> >
> >
> >> -----Original Message-----
> >> From: Gene Cumm [mailto:gene.cumm at gmail.com]
> >> Sent: Tuesday, May 17, 2016 1:07 PM
> >> To: Tal Lubko
> >> Cc: syslinux at zytor.com
> >> Subject: Re: [syslinux] Syslinux fwrite support
> >>
> >> On Tue, May 17, 2016 at 2:39 AM, Tal Lubko via Syslinux
> >> <syslinux at zytor.com> wrote:
> >> > Hi
> >> > Does Syslinux support fwrite for fat filesystem?Is it supported
> for
> >> other filesystem?As far as I understand the function exist but isn't
> >> fully implemented.Is that correct?
> >> > I also found this thread that says about the
> >> > samehttp://www.syslinux.org/archives/2011-August/017093.html
> >> > Thanks,Tal
> >>
> >> At this time, writing should only be supported for the ADV and raw
> >> sectors unless you're writing to a file over the network from a
> >> network boot like TFTP upload.  Writing to a filesystem beyond
> >> strictly overwriting contents of existing files byte for byte
> >> involves understanding allocation and checksum mechanisms involved.
> >> To my knowledge, no file system that Syslinux supports stores hashes
> >> of file contents into the file system metadata.
> >>
> >> Traditionally, Syslinux has taken the approach that we can not trust
> >> the BIOS calls for any writes beyond the ADV.
> >>
> >> Tal, what's the goal/use case for using fwrite()?  Is it perhaps
> >> something that could be solved using the ADV?  For example, the
> >> --once parameter to syslinux/extlinux changes the default for one
> boot.
> >>
> >> --
> >> -Gene
> > Hi
> >
> > The goal is some kind of boot log.
> 
> What about the real OS's logs?  What kind of a log?  timestamps of
> executing a COM32 and perhaps what command executed?  Reboot count?  A
> single entry of something?
> 
> > I understand it is possible by using raw sectors writing.
> > I couldn't find much documentation about ADV, but my guess that it
> wouldn’t do the job.
> 
> I'd say the ADV is likely not appropriate for this.
> 
> > BTW: Where can I find some explanation about ADV and --once
> parameter?
> 
> For --once:
> http://www.syslinux.org/wiki/index.php?title=Install#options
> 
> --
> -Gene
Hi Gene

Thanks a lot for your help.
OS's log won't do the job but raw writing sectors is good enough.

I think I understand the --once option but there aren't many details about it (for example where it is stored).
I also couldn't find any detailed documentation about the ADV option.

Tal




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