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

[ValdikSS]

On 05.10.2023 20:53, Vladimir 'phcoder' Serbinenko wrote:
> This has a very high risk of breaking existing configs. "Specification 
> allows" doesn't mean that real-world BIOSes actually react well to it. 
> Some BIOS may read just reads 63 instead of 127 sectors and we end up 
> with garbage in this case. I fill it shouldn't come into release. After 
> it we can discuss.

I've checked syslinux code, they also use 127 sector reads in LBA mode.
https://github.com/geneC/syslinux/blob/5e426532210bb830d2d7426eb8d8c154d9dfcba6/core/fs/diskio_bios.c#L349

GRUB has this limit as well, but it is not applied due to other constraints.
https://github.com/rhboot/grub2/blob/10f8ffc133553209ec1ddaadc6f4a8a25d3dea4e/grub-core/disk/i386/pc/biosdisk.c#L434

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.

If you believe that 127 sectors could break things, then this patch 
could be ignored. It provides only marginal speed-up vs 63 sectors.

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