Hi,
I am modifying GRUB for a Linux LiveOS, which boots into separate images
depends on
how much RAM presents on the system. GRUB has a memory map initialized, so I
think
it is relatively easy to do so.
However, I discovered this method only works on EFI systems, if I load it on
i386-pc
(not a real i386 PC, just using BIOS to boot), the memory usage returns 0.
Here's my code[1]:
grub-core/commands/phymem.c
grub_uint64_t total_mem_bytes = 0ULL;
static int
traverse_mmap_hook (grub_uint64_t addr, grub_uint64_t size, grub_memory_type_t
type,
void *data __attribute__ ((unused)))
{
total_mem_bytes += size;
}
grub_err_t
grub_cmd_phymem (...) {
grub_mmap_iterate (traverse_mmap_hook, NULL);
}
Then I convert the integer into a string and export to the environment
variables,
and print it out.
On EFI systems, I can get the correct amount of system memory:
grub> insmod phymem
grub> phymem
The total system memory is 16384 MiB.
However on BIOS systems, the result is zero:
grub> insmod phymem
grub> phymem
The total system memory is 0 MiB.
So, how can I detect the amount if RAM on non-EFI systems? If I recalled it
right,
GRUB can boot kernels which complies with Multiboot specification, so the memory
info should be always present. If I missed something, please point it out.
Thanks,
Cinhi Young
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