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

[Peter Maydell]

On Tue, 15 Nov 2022 at 14:51, Cédric Le Goater <clg@kaod.org> wrote:
>
> On 11/15/22 15:34, Peter Maydell wrote:
> > 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 ?
>
> That's ok because the blk_pread() call following, which loads in RAM
> the initial data, won't fail.
>
> It might be better to enforce a strict check on the size to avoid
> further confusion ? and change the error message to be clear.

Can we use blk_check_size_and_read_all() here rather than
a manual "check size, and then pread" ? That will take care
of the error message for you and make this device behave
the same way as other flash devices which use block backends.

thanks
-- PMM