[syslinux] Syslinux fwrite support

Gene Cumm gene.cumm at gmail.com
Sat May 21 06:43:50 PDT 2016

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


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