Re: I/O permissions for V86 tasks (Enhanced V86 Mode)?

Kendall Bennett (KendallB@scitechsoft.com)
Fri, 17 Jul 1998 12:38:23 -0800

> I appear to have been wrong about that. The tss->bitmap value contains a
> pointer to the start of the IO bitmap relative to the start of the TSS.
> So in theory the bitmap could be moved to the end of the TSS and made
> to be of variable size; the code which will need changing, apart from the
> definition of thread_struct, is...
>
> - the ioperm() code
> - the fork code in process.c which initialises the bitmap
> - the macro set_tss_desc and any code which uses it.
>
> If the IO bitmap is created with a default size then you might get away
> with not changing the code which allocates space for the thread_struct.
> The IO bitmap size will need to be stored somewhere - add an extra element
> to the thread_struct. I guess what will happen is if ioperm() is called
> with ports which are not covered by the bitmap it allocates a larger TSS.
> After doing that I guess it will need to cause a task switch.

Ok, I like this idea. I think I understand most of the above and am
willing to try hacking it into my kernel sources, but I am not clear
on two things:

1) If I reallocate space for the I/O bitmap, how would I do this? Is
there a krealloc() function or something to enlarge the size of a
kernel memory object? Or would I simply alloc a new one (do I use
malloc or something else?) for the larger size, copy the old TSS
to it, and free the old one? Or can I simply allocate an 8Kb
block for the new I/O bitmap and simply point the TSS at it (but
then I would need to free it later right?).

2) Once I have enlarged the memory block if the TSS has moved to a
new location how do I then inform the kernel that the TSS has
moved so it knows about it?

3) I understand the need to cause a task switch, but how would I
accomplish this?

Regards,

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