[PATCH 0/4] virtio-blk clarifications

On Mon, Sep 10, 2018 at 10:35:21AM +0200, Paolo Bonzini wrote:
> On 28/08/2018 14:27, Michael S. Tsirkin wrote: >
> On Fri, Aug 17, 2018 at 07:04:42PM +0200, Paolo Bonzini wrote: > >> Define them in terms of descriptors, not segments, and explain what the > >> driver and device are to use them for. > >> > >> Signed-off-by: Paolo Bonzini <> > >> --- > >>  content.tex
17 +++++++++++++---- > >>  1 file changed, 13 insertions(+), 4 deletions(-) > >> > >> diff --git a/content.tex b/content.tex > >> index 4cdfeef..fd3a3c2 100644 > >> --- a/content.tex > >> +++ b/content.tex > >> @@ -3515,11 +3515,11 @@ device except where noted. > >>  subsection{Feature bits}label{sec:Device Types / Block Device / Feature bits} > >>
> >>  egin{description} > >> -item[VIRTIO_BLK_F_SIZE_MAX (1)] Maximum size of any single segment is > >> -
in field{size_max}. > >> +item[VIRTIO_BLK_F_SIZE_MAX (1)] Maximum size of any single descriptor in > >> +
the data portion of a request ("segment") is in field{size_max}. > >>
> >> -item[VIRTIO_BLK_F_SEG_MAX (2)] Maximum number of segments in a > >> -
request is in field{seg_max}. > >> +item[VIRTIO_BLK_F_SEG_MAX (2)] Maximum number of descriptors in the > >> +
data portion of a request ("segments") is in field{seg_max}. > >>
> >>  item[VIRTIO_BLK_F_GEOMETRY (4)] Disk-style geometry specified in > >>
field{geometry}. > >> @@ -3762,6 +3762,10 @@ error or VIRTIO_BLK_S_UNSUPP for a request unsupported by device: > >>  A driver SHOULD NOT submit a request which would cause a read or write > >>  beyond field{capacity}. > >>
> >> +A driver SHOULD NOT submit a request which has more than field{seg_max} > >> +descriptors in the data portion, or which has more than field{size_max} > >> +bytes in a single descriptor in the data portion. > >> + > >>  A driver SHOULD accept the VIRTIO_BLK_F_RO feature if offered. > >>
> >>  A driver MUST set field{sector} to 0 for a VIRTIO_BLK_T_FLUSH request. > >> @@ -3782,6 +3786,11 @@ a range of sectors has been discarded. > >>  A device MUST set the field{status} byte to VIRTIO_BLK_S_IOERR for a > >>  request which would cause a read or write beyond field{capacity}. > >>
> >> +A device MAY set the field{status} byte to VIRTIO_BLK_S_IOERR for a > >> +request > >  >
> Well device can always do this for any request, right? >
> I think the distinction is that it can do this for all such requests? > >  > >> which has more than field{seg_max} descriptors in the data > >> +portion, or which has more than field{size_max} bytes in a single > >> +descriptor in the data portion. > >> + > >  >
> Since it's SHOULD NOT for driver, I think another assumption is that >
> device must handle such huge requests anyway then? >
> Not really, the idea was that it's okay if the driver sends huge
> requests, but it has to expect the error case.  OTOH the device is free
> to handle huge requests if it wishes to. >
> Paolo  Right but it must not crash or hang or set NEEDS_RESET as a result, right? It must use the request even if it's with error.  I think spec should clarify that.  >
> Do all host implementations actually satisfy this requirement? > >  > >>  A device MUST set the field{status} byte to VIRTIO_BLK_S_IOERR > >>  for a write request if the VIRTIO_BLK_F_RO feature if offered, and MUST NOT > >>  write any data. > >> --  > >> 2.17.1 > >> > >> > >> > >>

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