Large VHD image files

[fysnet]

If I have a considerably large VHD file, ~32Gig used/128Gig total usable size, Bochs returns a PANIC at line 325 in harddrv.cc

BX_PANIC(("ata%d-%d: could not open hard drive image file '%s'", channel, device, SIM->get_param_string("path", base)->getptr()));

The offending code is in vpc.cc, line 173:

if (sector_count >= 65535 * 16 * 255) {
  bx_close_image(fd, pathname);
  return -EFBIG;
}

I understand that the VHD specification states that a CHS value limit is 65535/16/63. However, this doesn't mean that Bochs shouldn't be able to access up to the actual 2TB limitation of the VHD when reading sectors, correct?

Therefore, what is the reason for the check at line 173 in vpc.cc shown above? I don't believe it is needed, unless there is somewhere in the Bochs source that relies on the limitation of a CHS value of 65535/16/63. The only limitation would be in the BIOS and it can't access anything past the 1024/254/63 mark anyway, right?

However, if it is actually needed, an additional error to the log file might be warranted. Maybe something like:

if (sector_count >= 65535 * 16 * 255) {
  bx_close_image(fd, pathname);
  BX_ERROR(("VHD file too large: " FMT_LL "u", sector_count));
  return -EFBIG;
}

Thank you,
Ben

[stlintel]

The VPC disk image code was ported from QEMU to Bochs.
I think you might try to look into QEMU code and see if the limitation is hard or not.
About the BX_ERROR -> just trivial, submit PR and it will be merged immediatelly

[fysnet]

See PR #79
This was ported from newer QEMU code.
https://gitlab.com/qemu-project/qemu/-/blob/master/block/vpc.c?ref_type=heads#L305