Re: [PATCH v2] m25p80: Improve error when the backend file size does not match the device

["Cédric Le Goater" <clg@kaod.org>]

On 11/16/22 07:56, Markus Armbruster wrote:
> Cédric Le Goater <clg@kaod.org> writes:
> 
>> 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.
>>
>> Use blk_check_size_and_read_all() instead of blk_pread() to improve
>> the reported error.
>>
>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
>> ---
>>   hw/block/m25p80.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
>> index 02adc87527..68a757abf3 100644
>> --- a/hw/block/m25p80.c
>> +++ b/hw/block/m25p80.c
>> @@ -24,6 +24,7 @@
>>   #include "qemu/osdep.h"
>>   #include "qemu/units.h"
>>   #include "sysemu/block-backend.h"
>> +#include "hw/block/block.h"
>>   #include "hw/qdev-properties.h"
>>   #include "hw/qdev-properties-system.h"
>>   #include "hw/ssi/ssi.h"
>> @@ -1614,8 +1615,7 @@ static void m25p80_realize(SSIPeripheral *ss, Error **errp)
>>           trace_m25p80_binding(s);
>>           s->storage = blk_blockalign(s->blk, s->size);
>>   
>> -        if (blk_pread(s->blk, 0, s->size, s->storage, 0) < 0) {
>> -            error_setg(errp, "failed to read the initial flash content");
>> +        if (!blk_check_size_and_read_all(s->blk, s->storage, s->size, errp)) {
>>               return;
>>           }
>>       } else {
> 
> Ignorant question: what does blk_pread() on short read?  Does it fail?

an underlying call to blk_check_byte_request() makes it fail.

> Or does it succeed, returning how much it read?  I tried to find an
> answer in function comments, no luck.
> 
> Are there more instances of "we fill some fixed-size memory (such as a
> ROM or flash) from a block backend?"

Yes. There are other similar devices :  nand, nvram, pnv_pnor, etc.

C.