Re: status grub2 port of grub-legasy map command

[John Stanley <jpsinthemix@verizon.net>]

Ok, that sounds good... I feel better about it then. I didn't mean 
directly modifying bios data, but through doc'd bios ints of course. It 
been a long, long time since I've looked at (or dealt with) bios code, 
so I was was simply wondering if boot device naming  could be modified  
in  a  documented way nowadays-- after all, the functionality has been 
available in the bios setup in pcs for at least 10 years or so.

Vladimir Serbinenko wrote:
>
>
> On Sat, Apr 18, 2009 at 1:12 AM, John Stanley <jpsinthemix@verizon.net 
> <mailto:jpsinthemix@verizon.net>> wrote:
>
>     Hi Javier and all,
>     I could probably have a version of the drivemap completed this
>     weekend as well, but since I've basically simply adapted your
>     drivempa.patch.8 to r2106, with little change, I'd be more
>     comfortable going with your new patch since you know the code much
>     better.
>
>     In addition, in the last several days,  have started leaning away
>     from it altogether -- because of the use  of an int13 intercept
>     TSR. When I started looking at the drivemap patch about a week
>     ago, I assumed it simply did some sort of bios (internal) table
>     swapping only. I'm not really comfort able with the int13 handler
>     redirect. I worry about (possibly rare) problems downstream while
>     running Windows. On the other hand, I know it "does work," as I
>     and many others have been using map with grub-legasy for several
>     years now. Nevertheless, I'm now a bit apprehensive.
>
> Modifying internal bios tables isn't practicable because they may be 
> anywhere and in any format. Windows follows the memory map supplied by 
> int12/int15/bda which says that the ranges used by hook are unusable. 
> Also even if windows overwrites int13 handle it doesn't matter at all 
> because windows switches to its own disk drivers after initial start
>
>
>     For me, for the time-being, as my laptops are all Thinkpads, which
>     have bios supplied "boot device table"  functionality (via f12 on
>     poweron), I can live without drivemap for those occasions when I
>     need to come down from the hilltop to work on Windows.
>
>     What I'd like to do with drivemap, is to do boot device swapping
>     by changing in the bios which device is to be treated as the
>     "first" boot device, which is the second, etc. I know this is
>     doable in principle, but it may not be practical, or wise-- I'm
>     not sure. 
>
> There is no public API to do so. So you need to reverse engineer BIOS 
> which is impractical to do for every possible mobo.
>
>      It would also have to be done in a way which does not "pull the
>     rug out on grub" insofar as boot device enumeration is concerned.
>
>
>     Javier Martín wrote:
>
>         Hello there. I am the original author of the drivemap command.
>         I was
>         told by a friend that it was being discussed again on the GRUB
>         list, so
>         I came back and examined the two new enabling functionalities,
>         preboot
>         hooks and mmap. I've adapted drivemap to use them both, and I'm
>         polishing some rough edges. I might send a new version of the
>         patch this
>         weekend. Should people, however, prefer John's version, I'd be
>         glad to
>         assist.
>
>         El mié, 15-04-2009 a las 11:34 +0200, phcoder escribió:
>          
>
>             Yes it is. Also it's better to use grub_mmap_iterate
>             instead of basing the location on 0x413 value. How to do
>             it look at mmap/i386/pc/mmap.c
>                
>
>         The preboot hooks patch works beautifully. However, mmap
>         causes some
>         sort of glitch that makes FreeDOS (one of my three drivemap tests,
>         together with ReactOS and XP) triple-fault. I've been trying
>         to debug it
>         with GDB-over-QEMU, but it is a real PITA. I haven't found any
>         sort of
>         bug in the mmap code, so I'm quite dumbfounded right now.
>         Nevertheless,
>         I'm proceeding to the XP test, which would likely be the most
>         common use
>         case for drivemap.
>
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