Re: [RFC] Platform information services

["Vesa Jääskeläinen" <chaac@nic.fi>]

Javier Martín wrote:
> I take that by "convenient to use" and your earlier "code safety"
> reference, you imply a function that returns a typed pointer to the
> structure, like "bda* var = grub_getbda();" in i386-pc, so that fields
> of such struct can be directly accessed by var->free_mem_kb.
> 
> However, this requires that a function is created for each firmware
> structure that is deemed interesting by GRUB developers. In this
> proposal, only one (very lightweight) function is created and then IDs
> are defined for the structs. WRT "code safety", malloc and friends also
> return a void* that you have to cast, so nothing new under the sky.

In your case there is really no change.

You create new switch branch (which is most likely implemented by
function somewhere).

In order to access this void * you have to know its contents. Why not
use structure to define its contents where viable?

When using malloc() you know that memory returned is not formatted in
anyway. Therefore it is safe to cast.

You just want to make it more complex that it needs to be in my eyes.

>> You have still not provided a single GOOD example where this would be
>> used AND would provide some ADDED VALUE. Unless you provide a convincing
>> one (while I pretty much doubt) I do not see this feature to be in our
>> official tree.
> An use case would be in the proposed drivemap module, in the function
> installing an interrupt handler in the real-mode IVT: instead of the
> current code with magic addresses,
> 
> /* Real mode IVT slot (seg:off far pointer) for interrupt 0x13.  */
> grub_uint32_t *ivtslot = (grub_uint32_t*)0x0000004c;
> 
> The module could be like this:
> 
> /* Real mode IVT slot (seg:off far pointer) for interrupt 0x13.  */
> grub_uint32_t *ivtslot = 19 +
> (grub_uint32_t*)grub_machine_get_fwstruct(GRUB_I386_PC_IVT);

The better way that complies with all your error cases provided:

grub_ivt_entry_t *entry;
entry = grub_get_ivt_entry(0x13);
*entry = new_value;

of course grub_ivt_entry_t could be renamed to be something like
grub_realmode_addr_t.

.