Re: Implement standard file operation with QEMU

[Philippe Mathieu-Daudé]

Hi Xiaolei,

+Laurent (user-mode)
+Alex (semihosting)
+Marc-André (chardev)

On 7/16/20 2:51 AM, casmac wrote:
> Hi all,
>   I am trying to implment standard file operation (stdio) with QEMU for
> DSP architecture. The manufacture (TI) provides a runtime library that
> support posix standard IO, but it left the device level implmentation as
> hook function calls, like in the library source , it contains 
> add_device() function, and write(),read(),open() are not implemented:
> 
> int add_device(char      *name,
>                unsigned   flags,
>                int      (*dopen)  (const char *path, unsigned flags, int
> foo),
>                int      (*dclose) (int fno),
>                int      (*dread)  (int fno, char *buf, unsigned count),
>                int      (*dwrite) (int fno, const char *buf, unsigned
> count),
>                fpos_t     (*dlseek) (int fno, fpos_t offset, int origin),
>                int      (*dunlink)(const char *path),
>                int      (*drename)(const char *old_name, const char
> *new_name))
> {
>    _DEVICE *dt;
> 
>    strncpy(dt->name,name,8);
>    dt->name[8] = '\0';
>    dt->flags   = flags;
>    dt->OPEN    = dopen;
>    dt->CLOSE   = dclose;
>    dt->READ    = dread;
>    dt->WRITE   = dwrite;
>    dt->LSEEK   = dlseek;
>    dt->UNLINK  = dunlink;
>    dt->RENAME  = drename;
> }
> 
> int write(int           fildes,
>           const char   *bufptr,
>           unsigned      cnt)
> {
>   
> /*------------------------------------------------------------------------*/
>    /* CALL FUNCTION FROM DEVICE TABLE TO PERFORM WRITE FOR THIS
> DEVICE/FILE  */
>   
> /*------------------------------------------------------------------------*/
>    return (*(_stream[fildes]->WRITE)) (fildes,bufptr,cnt);
> }
> 
>    Then, how can we use this runtime library together with QEMu to
> implement full-stack file oerations?  I really appreaciate any advice.

Trying to understand...

Are you trying to ask "how to implement semihosting for my
qemu-user-tidsp fork"?

Have a look at "hw/semihosting/console.h" and the implementation
(so far only ARM) of qemu_semihosting_console_[in/out].
This might help to plug read/write. Using other stream than
stdin/stdout is not supported (but you can add support) so
open/lseek/close/rename/unlink are not considered.

(for QEMU 'console' is the stdin/stdout subset of stdio).

You can redirect semihosted files with any host chardev,
this is done in qemu_semihosting_connect_chardevs().

You might also have a look at the functions declared in
"hw/semihosting/semihost.h" and how the different TCG helpers
use them.

Regards,

Phil.