Re: [dmidecode] dmidecode for DOS?

[Jean Delvare]

Hi Ian,

[Ian Anderson]
> Got in touch with Eric Auer over at FreeDOS and his suggestion was
> to use _farpeekb or DPMI access.
> 
> http://www.delorie.com/djgpp/doc/libc-2.02/libc_270.html
> 
> or
> 
> http://www.delorie.com/djgpp/doc/libc-2.02/libc_8.html
> 
> _farpeekb seems a lot simpler.  If I am reading your code correctly
> (50/50 chance of that), and recall the compiler error message it
> appears there is only one line in mem_chunk -- mmp=mmap(0,
> mmoffset+len, PROT_READ, MAP_SHARED, fd, base-mmoffset); that needs to
> be changed,

It's a bit more complex than that. There are two memory access
implementations in dmidecode currently, one using lseek+read, one using
mmap. Only one is selected at compilation time (although I plan to move
the choice to run time instead.) Both rely on /dev/mem ultimately, that
is, the memory is accessed as a file. In the case of DOS we will instead
be accessing the low memory directly, so a lot of code can go away.

> unfortunately _farpeekb takes a different number of arguements, so
> where to start? :S

I'm taking my chance. Note that I have no DOS/DJGPP environment to test
the code, so read it as "that's where I would start" and try to fix the
problems yourself from there.

#include <sys/farptr.h>

void *mem_chunk(size_t base, size_t len, const char *devmem)
{
        void *p;
        size_t i;

        if((p=malloc(len))==NULL)
        {
                perror("malloc");
                return NULL;
        }
        
        _farsetsel(_dos_ds);
        for(i=0; i<len; i++)
        {
                *((char *)p+i)=_farnspeekb(base+i);
        }

        return p;
}

Note that the code above will trigger a warning about devmem not being
used, but you can ignore it safely.

This is certainly not the most efficient method (a direct memcpy from
the lower memory range would be better) but that might work. Maybe DPMI
can do that faster but I wouldn't know where to start. A more simple
optimization would be to use _farnspokel instead of _farnspeekb, you
just have to allocate a few more bytes. Note that there may be memory
alignment issues though.

void *mem_chunk(size_t base, size_t len, const char *devmem)
{
        void *p;
        size_t i;

        if(len%sizeof(long))
        {
                len+=sizeof(long)-len%sizeof(long);
        }

        if((p=malloc(len)==NULL)
        {
                perror("malloc");
                return NULL;
        }
        
        _farsetsel(_dos_ds);
        for(i=0; i*sizeof(long)<len; i++)
        {
                *((long *)p+i)=_farnspeekb(base+i*sizeof(long));
        }

        return p;
}

Again I couldn't try this code so it's most certainly bogus, but at
least now you have an idea where to start :)

-- 
Jean Delvare