Re: [PATCH 0/1] hw/arm/aspeed: Automatically zero-extend flash images

[Peter Delevoryas]

On Tue, Nov 15, 2022 at 02:06:57PM +0100, Cédric Le Goater wrote:
> Hello Peter,
> 
> On 11/14/22 20:08, Peter Delevoryas wrote:
> > I've been using this patch for a long time so that I don't have to use
> > dd to zero-extend stuff all the time. It's just doing what people are
> > doing already, right? I hope it's not controversial.
> 
> I simply run :
> 
>    truncate --size <size>

Ohhh I always forget about that command. That's certainly easier
than what I was doing.

> 
> on the FW file when needed and it is rare because most FW image builders
> know the flash size of the target.

welllllll my yocto builds don't, I'm not sure we would want them to either?

Because that would be extra data with no value to transfer to the BMC/etc.

flashcp erases the whole flash initially, which is why I don't worry
about providing a firmware image that is only covering the first 30 MB of
flash.

> 
> However, the current error message is confusing and the following could
> be an improvement :
> 
> @@ -1606,6 +1606,13 @@ static void m25p80_realize(SSIPeripheral
>      if (s->blk) {
>          uint64_t perm = BLK_PERM_CONSISTENT_READ |
>                          (blk_supports_write_perm(s->blk) ? BLK_PERM_WRITE : 
> 0);
> +
> +        if (blk_getlength(s->blk) != s->size) {
> +            error_setg(errp, "backend file is too small for flash device %s 
> (%d MB)",
> +                       object_class_get_name(OBJECT_CLASS(mc)), s->size >> 
> 20);
> +            return;
> +        }
> +
>          ret = blk_set_perm(s->blk, perm, BLK_PERM_ALL, errp);
>          if (ret < 0) {
>              return;
> 
> I can send a patch for the above.

Ohhh yay! Thanks!

> 
> <hack>
> 
> I mostly run the QEMU machines with -snapshot, this hack  :
> 
>   blk_set_allow_write_beyond_eof(s->blk, true);
> 
> makes it work also ...

!!! Ohhh! interesting...that seems more sketchy but certainly simpler.

> 
> </hack>
> 
> 
> Thanks,
> 
> C.
> 
> > One note: I couldn't figure out how to make it work without changing the
> > permissions on the block device to allow truncation. If somebody knows
> > how to avoid the `blk_get_perm`, `blk_set_perm` calls here, let me know!
> > 
> > Thanks,
> > Peter
> > 
> > Peter Delevoryas (1):
> >    hw/arm/aspeed: Automatically zero-extend flash images
> > 
> >   hw/arm/aspeed.c | 40 +++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 39 insertions(+), 1 deletion(-)
> > 
>