Increase the value from 63 to speed up reading process. This commit increases two limits: the low-level int 13h reading code and a high-level reading code with disk cache. The disk cache imposes an overall limitation of a higher-layer reading code. The original comment regarding 16K is incorrect, it was 512<<6 = 32768, and now it is 512<<7 = 65536.
According to [Wikipedia][1] and [OSDev][2], the upper safe value for LBA read using IBM/MS INT13 Extensions is 127 sectors due to the limitations of some BIOSes. GRUB [already enforced][3] the limit, but it was no-op due to other constraints. This value is also used in [syslinux][4]. As we're now reading up to 127 sectors of 512 bytes, we need to be able to store in the cache up to 65024 bytes. Without this change, GRUB wouldn't try to read more than 64 sectors at once (even if the lower reading layer allows it). [1]: https://en.wikipedia.org/wiki/INT_13H#INT_13h_AH=42h:_Extended_Read_Sectors_From_Drive [2]: https://wiki.osdev.org/Disk_access_using_the_BIOS_(INT_13h)#LBA_in_Extended_Mode [3]: https://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/disk/i386/pc/biosdisk.c?h=grub-2.12-rc1#n430 [4]: https://repo.or.cz/syslinux.git/blob/refs/tags/syslinux-6.03:/core/fs/diskio_bios.c#l349 Signed-off-by: ValdikSS <i...@valdikss.org.ru> --- include/grub/disk.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/grub/disk.h b/include/grub/disk.h index be032a72c..608deb034 100644 --- a/include/grub/disk.h +++ b/include/grub/disk.h @@ -184,14 +184,14 @@ typedef struct grub_disk_memberlist *grub_disk_memberlist_t; #define GRUB_MDRAID_MAX_DISKS 4096 /* The size of a disk cache in 512B units. Must be at least as big as the - largest supported sector size, currently 16K. */ -#define GRUB_DISK_CACHE_BITS 6 + largest supported sector size, currently 64K. */ +#define GRUB_DISK_CACHE_BITS 7 #define GRUB_DISK_CACHE_SIZE (1 << GRUB_DISK_CACHE_BITS) #define GRUB_DISK_MAX_MAX_AGGLOMERATE ((1 << (30 - GRUB_DISK_CACHE_BITS - GRUB_DISK_SECTOR_BITS)) - 1) /* Maximum number of sectors to read in LBA mode at once */ -#define GRUB_DISK_MAX_LBA_SECTORS 63 +#define GRUB_DISK_MAX_LBA_SECTORS 127 /* Return value of grub_disk_native_sectors() in case disk size is unknown. */ #define GRUB_DISK_SIZE_UNKNOWN 0xffffffffffffffffULL -- 2.41.0 _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
