Re: [Qemu-devel] [PATCH] hw/block: report when pflash backing file isn't aligned

[Laszlo Ersek <lersek@redhat.com>]

On 02/14/19 16:57, Alex Bennée wrote:
> It looks like there was going to be code to check we had some sort of
> alignment so lets replace it with an actual check. This is a bit more
> useful than the enigmatic "failed to read the initial flash content"
> when we attempt to read the number of bytes the device should have.
> 
> This is a potential confusing stumbling block when you move from using
> -bios to using -drive if=pflash,file=blob,format=raw,readonly for
> loading your firmware code.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  hw/block/pflash_cfi01.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/block/pflash_cfi01.c b/hw/block/pflash_cfi01.c
> index bffb4c40e7..f3251b236c 100644
> --- a/hw/block/pflash_cfi01.c
> +++ b/hw/block/pflash_cfi01.c
> @@ -722,12 +722,19 @@ static void pflash_cfi01_realize(DeviceState *dev, Error **errp)
>      }
>      device_len = sector_len_per_device * blocks_per_device;
>  
> -    /* XXX: to be fixed */
> -#if 0
> -    if (total_len != (8 * 1024 * 1024) && total_len != (16 * 1024 * 1024) &&
> -        total_len != (32 * 1024 * 1024) && total_len != (64 * 1024 * 1024))
> -        return NULL;
> -#endif
> +    /*
> +     * Validate the backing store is the right size for pflash
> +     * devices. It has to be padded to a multiple of the flash block
> +     * size.
> +     */
> +    if (pfl->blk) {
> +        uint64_t backing_len = blk_getlength(pfl->blk);
> +        if (device_len != backing_len) {
> +            error_setg(errp, "backing file wrong size "
> +                       "(%" PRId64 " != %" PRId64")", backing_len, device_len);
> +            return;
> +        }
> +    }
>  
>      memory_region_init_rom_device(
>          &pfl->mem, OBJECT(dev),
> 

I have two suggestions:
- backing_len and device_len are both uint64_t; we should print them
  with PRIu64
- from a user POV, I find it more useful if the error message also shows
  which quantity is which, not just two inequal numbers.

I don't feel too strongly about this, so up to you.

Thanks,
Laszlo