请教关于 grub4dos 读取 gpt 磁盘的问题

wintoflash

请问 grub4dos 读取 GPT 分区表磁盘时，会不会忽略 protective MBR 里面记录的分区信息 (比如 CHS)?

如果 protective MBR 里面的分区 CHS 之类的全是乱的，会不会导致 grub4dos 不认这个磁盘？

wintoflash

2011yaya2007777 发表于 2020-5-31 19:53
首先要判断是否为有效的MBR分区表，因此不会忽略分区表信息。

如果只有 CHS 是乱填的，会不会有影响？

wintoflash

不点 发表于 2020-5-31 20:35
grub4dos 在读盘时，首先要确定 c/h/s 的值，以及 lba 的支持与否。如果确定不了这些关键信息，那就无法进 ...

是这样的，这个问题来自 https://github.com/a1ive/grub/issues/26

NOTE:For partitions which begin or end beyond  the 1024th cylinder, the three CHS bytes should always be filled with: FE FF FF ; which are decoded as follows:Byte 1:  FEh = 254  for a total of 255 heads.Bytes 2 and 3:  FFh and FFh — split into two full binary counts of 6 bits (11 1111; 3Fh = 63 sectors), and 10 bits (11 1111 1111) or 3FFh = 1023 for a total of 1024 cylinders. CHS: 1023, 254, 63.This tuple corresponds to an LBA sector of: 16450559. That's a point where about  8.4 GB of hard disk sectors could be accessed (16,450,560 sectors * 512 bytes/sector = 8,422,686,720 bytes).16-byte partition table entries can not exceed 1024 cylinders for their Starting and Ending CHS bytes!  When utility programs display CHS tuples with a cylinder value larger than 1023, they can only do so by computing pseudo-CHS values from the 4-byte "Starting Sector" or "Partition Size" values.

如果是一个很大的分区，chs应该是 fe ff ff，但是根据uefi的规范，gpt分区表硬盘的mbr上chs应该填 ff ff ff。

wintoflash

2011yaya2007777 发表于 2020-5-31 21:13
应该不会这样规定吧。在哪个文件里？我觉得应当是feffff.

Set to the CHS address of the last logical block on the disk. Set to 0xFFFFFF if it is not possible to represent the value in this field.

https://uefi.org/sites/default/f ... pec_2_8_A_Feb14.pdf
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