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

[ValdikSS via Grub-devel]

On 06.10.2023 21:34, ValdikSS wrote:

What can change my mind:

1) Proof that windows does such calls

Windows XP **bootloader** uses single-sector reads with int 13h to read the kernel (just checked with qemu). But the kernel seem to use direct IDE controller method reading.

disk_op d=0x000f3a20 lba=1145839 buf=0x00030000 count=5 cmd=2
disk_op d=0x000f3a20 lba=1145844 buf=0x00030000 count=59 cmd=2
disk_op d=0x000f3a20 lba=1145903 buf=0x00030000 count=4 cmd=2
disk_op d=0x000f3a20 lba=1145907 buf=0x00030000 count=60 cmd=2
disk_op d=0x000f3a20 lba=1145967 buf=0x00030000 count=3 cmd=2
disk_op d=0x000f3a20 lba=1145970 buf=0x00030000 count=61 cmd=2
disk_op d=0x000f3a20 lba=1146031 buf=0x00030000 count=2 cmd=2
disk_op d=0x000f3a20 lba=1146033 buf=0x00030000 count=62 cmd=2
disk_op d=0x000f3a20 lba=1146095 buf=0x00030000 count=1 cmd=2
disk_op d=0x000f3a20 lba=1146096 buf=0x00030000 count=63 cmd=2
disk_op d=0x000f3a20 lba=1146159 buf=0x00030000 count=63 cmd=2
disk_op d=0x000f3a20 lba=1146222 buf=0x00030000 count=1 cmd=2
disk_op d=0x000f3a20 lba=1146223 buf=0x00030000 count=62 cmd=2
disk_op d=0x000f3a20 lba=1146285 buf=0x00030000 count=2 cmd=2
disk_op d=0x000f3a20 lba=1146287 buf=0x00030000 count=61 cmd=2

syslinux reads by 127 all the time

disk_op d=0x000f3a20 lba=6544 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=6671 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=6798 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=6925 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=7052 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=7179 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=7306 buf=0x00010000 count=127 cmd=2
disk_op d=0x000f3a20 lba=7433 buf=0x00010000 count=127 cmd=2

Currently GRUB falls back to CHS reading if LBA has failed.

I was checking in the wrong place. Now, checking with seabios, Windows XP bootloader is reading by a single sector, and the kernel uses up to 63 sectors reading.

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