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

[Markus Armbruster]

Alex Bennée <address@hidden> writes:

> Laszlo Ersek <address@hidden> writes:
>
>> 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 <address@hidden>
>>> ---
>>>  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
>
> blk_getlength actually returns int64_t for some reason (do signed
> lengths even make sense? maybe it's for error handling?). But sure I can
> make it PRIu64

Use of signed integers for file offsets is pervasive in the block layer.
It's convenient when we return either a non-negative offset or a
negative error code.  It's admittedly sloppy anywhere else.

>> - from a user POV, I find it more useful if the error message also shows
>>   which quantity is which, not just two inequal numbers.
>
> How about:
>
>   "backing file size (%) not enough for whole device (%)"
>
> ?

Not bad.  Another one, avoiding parentheses:

    "device needs DDD bytes, backing file provides only BBB bytes"

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