Re: RFC: Access to device drivers with mmap()

[Mohammad-Reza Nabipoor]

Hi Andreas.

On Mon, Jan 01, 2024 at 12:38:57PM +0100, Andreas Klinger wrote:
> Hi,
> 
> I'm writing Linux device drivers in which there is a mmap() file operation for
> mapping the memory from the kernel driver to the userspace. These drivers have
> no read() or write() functions.
> 
> I would like to investigate the content of this memory area with poke as it
> contains structured data (mostly picture images).
> 
> What I've seen so far is that poke is always accessing an opened file with
> lseek(), read(), write() but never with mmap() what I would need in my case.
> 
> Or did I miss something?
> 


1. One option is using libpoke and introducing a new "Foreign Device Interface" 
 using
   `pk_register_iod' function and by implementing the `struct pk_iod_if'.  See 
at the end of `libpoke.h'.
   Then, you can run your Poke scripts on your program that is using libpoke.

   The down-side is you don't benefit from `poke' CLI program.  It'll be an 
independent app.

2. The other option is to introduce a new IO space in libpoke.  See 
`libpoke/ios.c' file.

   Here you can see the supported IO Space Devices:

```
enum
{
  IOS_DEV_ZERO,
  IOS_DEV_MEM,
  IOS_DEV_STREAM,
  IOS_DEV_NBD,
  IOS_DEV_PROC,
  IOS_DEV_SUB,
  IOS_DEV_FILE, /* File must be last */
};

static const struct ios_dev_if *ios_dev_ifs[] =
  {
    [IOS_DEV_ZERO] = &ios_dev_zero,
    [IOS_DEV_MEM] = &ios_dev_mem,
    [IOS_DEV_STREAM] = &ios_dev_stream,
#ifdef HAVE_LIBNBD
    [IOS_DEV_NBD] = &ios_dev_nbd,
#else
    [IOS_DEV_NBD] = NULL,
#endif
#ifdef HAVE_PROC
    [IOS_DEV_PROC] = &ios_dev_proc,
#else
    [IOS_DEV_PROC] = NULL,
#endif
    [IOS_DEV_SUB] = &ios_dev_sub,
    [IOS_DEV_FILE] = &ios_dev_file, /* File must be last */
  };


Then you can see implementation for each of them in the corresponding 
`libpoke/ios-dev-$name.c' file.


> Would it be possible to introduce a new command (.mmap) for this purpose?
>


See `poke/pk-cmd-ios.c'.


> If yes, I would also participate in development.
> 


You are very welcome!
You can also join us in IRC: #poke on libera.chat servers.


Regards,
Mohammad-Reza