Re: [PATCH 0/2] disk: use maximum number of sectors for LBA

[Glenn Washburn]

On Fri,  7 Jul 2023 00:39:46 +0300
ValdikSS via Grub-devel <grub-devel@gnu.org> wrote:

> GRUB2 limits number of sectors read at once in LBA mode to the
> number reported in CHS disk geometry by BIOS.
> This is unnecessary, as IBM/MS INT13 Extensions allows reading
> up to 127 sectors in a single call.

Please provide more documentation for this. Wikipedia[1] suggests that
IBM/MS INT13 Extensions allows reading up to 64K sectors in a single
call. But that "some Phoenix BIOSes are limited to a maximum of 127
sectors". So the above seems misleading.

> 
> This fixes greatly increased boot times on WYSE C10LE x86 thin
> client with Phoenix bios.
> 
> See: https://lists.gnu.org/archive/html/grub-devel/2023-07/msg00001.html

First, this seems risky to me to be added for the release.  Why do we
believe that some other bios doesn't have a limit less than 127?

Also, based on reading the email in the link above, am I correct in
concluding that your bios set the CHS values returned in
grub_biosdisk_rw_int13_extensions() from the values in the MBR?

Glenn

[1]
https://en.wikipedia.org/wiki/INT_13H#INT_13h_AH=42h:_Extended_Read_Sectors_From_Drive