Re: [PATCH] m25p80: Warn the user when the backend file is too small for the device

[Peter Maydell]

On Tue, 15 Nov 2022 at 14:22, Cédric Le Goater <clg@kaod.org> wrote:
>
> Currently, when a block backend is attached to a m25p80 device and the
> associated file size does not match the flash model, QEMU complains
> with the error message "failed to read the initial flash content".
> This is confusing for the user.

The commit message says we get an unhelpful error if the
file size "does not match"...

> Improve the reported error with a new message regarding the file size.
>
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---
>  hw/block/m25p80.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
> index 02adc87527..e0515e2a1e 100644
> --- a/hw/block/m25p80.c
> +++ b/hw/block/m25p80.c
> @@ -1606,6 +1606,14 @@ static void m25p80_realize(SSIPeripheral *ss, Error 
> **errp)
>      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) {

...but the code change is only checking for "too small".

What happens if the user provides a backing file that is too large ?

> +            error_setg(errp,
> +                       "backend file is too small for flash device %s (%d 
> MB)",
> +                       object_class_get_name(OBJECT_CLASS(mc)), s->size >> 
> 20);

This potentially reports to the user a size which isn't the
right one for them to use to set the size of the backing file,
if that required size isn't an exact number of MB.

> +            return;
> +        }
> +
>          ret = blk_set_perm(s->blk, perm, BLK_PERM_ALL, errp);
>          if (ret < 0) {
>              return;
> --
> 2.38.1

thanks
-- PMM