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Date: Mon, 08 Sep 2014 15:49:22 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized
 read/write requests
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To: =?windows-1252?Q?Beno=EEt_Canet?= <benoit.canet@irqsave.net>, Peter Lieven <pl@kamp.de>
Cc: kwolf@redhat.com, ronniesahlberg@gmail.com, qemu-devel@nongnu.org, stefanha@redhat.com, mreitz@redhat.com

Il 08/09/2014 15:44, Beno=EEt Canet ha scritto:
>> > +    if (bs->bl.max_transfer_length && nb_sectors > bs->bl.max_trans=
fer_length) {
>> > +        error_report("read of %d sectors at sector %ld exceeds devi=
ce max"
>> > +                     " transfer length of %d sectors.", nb_sectors,=
 sector_num,
>> > +                     bs->bl.max_transfer_length);
>> > +        return -EINVAL;
>> > +    }
>> > +
>> >      return bdrv_co_do_preadv(bs, sector_num << BDRV_SECTOR_BITS,
>> >                               nb_sectors << BDRV_SECTOR_BITS, qiov, =
flags);
>> >  }
>> > @@ -3507,6 +3514,13 @@ static int coroutine_fn bdrv_co_do_writev(Blo=
ckDriverState *bs,
>> >          return -EINVAL;
>> >      }
>> > =20
>> > +    if (bs->bl.max_transfer_length && nb_sectors > bs->bl.max_trans=
fer_length) {
>> > +        error_report("write of %d sectors at sector %ld exceeds dev=
ice max"
>> > +                     " transfer length of %d sectors.", nb_sectors,=
 sector_num,
>> > +                     bs->bl.max_transfer_length);
>> > +        return -EINVAL;
>> > +    }
>> > +
>> >      return bdrv_co_do_pwritev(bs, sector_num << BDRV_SECTOR_BITS,
>> >                                nb_sectors << BDRV_SECTOR_BITS, qiov,=
 flags);
>> >  }
>> > --=20
>> > 1.7.9.5
>> >=20
>> >=20
> Look like you are changing the coroutine version.
>=20
> Some hardware like virtio-blk uses the AIO version of read and writes.
> What would happen if all the block drivers down the chain are AIO enabl=
ed ?

The AIO version still goes through bdrv_co_do_readv/writev.

However, error_report is not something you can use for guest-accessible
error messages, unless you want your logs to fill up with error messages.=
 :)

Paolo