Re: [PATCH v7 6/8] config: add check to block layer

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Aug 23, 2022 at 12:25:23PM +0800, Sam Li wrote:
> Stefan Hajnoczi <stefanha@redhat.com> 于2022年8月23日周二 08:54写道：
> >
> > On Tue, Aug 16, 2022 at 02:25:20PM +0800, Sam Li wrote:
> > > Putting zoned/non-zoned BlockDrivers on top of each other is not
> > > allowed.
> > >
> > > Signed-off-by: Sam Li <faithilikerun@gmail.com>
> > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > ---
> > >  block.c                          | 14 ++++++++++++++
> > >  block/raw-format.c               |  1 +
> > >  include/block/block_int-common.h |  5 +++++
> > >  3 files changed, 20 insertions(+)
> > >
> > > diff --git a/block.c b/block.c
> > > index bc85f46eed..affe6c597e 100644
> > > --- a/block.c
> > > +++ b/block.c
> > > @@ -7947,6 +7947,20 @@ void bdrv_add_child(BlockDriverState *parent_bs, BlockDriverState *child_bs,
> > >          return;
> > >      }
> > >
> > > +    /*
> > > +     * Non-zoned block drivers do not follow zoned storage constraints
> > > +     * (i.e. sequential writes to zones). Refuse mixing zoned and non-zoned
> > > +     * drivers in a graph.
> > > +     */
> > > +    if (!parent_bs->drv->supports_zoned_children &&
> > > +        child_bs->bl.zoned != BLK_Z_HM) {
> >
> 
> Should be:
> +if (!parent_bs->drv->supports_zoned_children &&
> +        child_bs->bl.zoned == BLK_Z_HM)
> 
> > Is this logical expression correct:
> >
> >   If the parent does not support zoned children and the child is not
> >   zoned, fail with an error.
> >
> > ?
> 
> No. It should be:
> 
> If the parent does not support zoned children and the child is zoned,
> fail with an error.  It should handle the case where a filter node is
> inserted above a raw block driver with a zoned_host_device child.
> 
> There are some QEMU command-line constraints for the zoned devices. I
> was wondering where to add such support so that it can print an error
> message for users:
> 1. cache.direct= setting

The O_DIRECT requirement is specific to file-posix and Linux's zoned
block device implementation, so it belongs in file-posix.c's
zoned_host_device .bdrv_file_open() function.

> 2. mix zoned/non-zoned drivers

This is generic and I think bdrv_add_child() is the right place for
parent-child compatibility checks.

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