Re: [Qemu-devel] [RFC PATCH 11/41] vvfat: Implement .bdrv_child_perm()

[Kevin Wolf]

Am 15.02.2017 um 18:30 hat Max Reitz geschrieben:
> On 13.02.2017 18:22, Kevin Wolf wrote:
> > vvfat is the last remaining driver that can have children, but doesn't
> > implement .bdrv_child_perm() yet. The default handlers aren't suitable
> > here, so let's implement a very simple driver-specific one that protects
> > the internal child from being used by other users as good as our
> > permissions permit.
> > 
> > Signed-off-by: Kevin Wolf <address@hidden>
> > ---
> >  block/vvfat.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index c6bf67e..7246432 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -3052,6 +3052,18 @@ err:
> >      return ret;
> >  }
> >  
> > +static void vvfat_child_perm(BlockDriverState *bs, BdrvChild *c,
> > +                             const BdrvChildRole *role,
> > +                             uint64_t perm, uint64_t shared,
> > +                             uint64_t *nperm, uint64_t *nshared)
> > +{
> > +    assert(role == &child_vvfat_qcow);
> > +
> > +    /* This is a private node, nobody should try to attach to it */
> > +    *nperm = BLK_PERM_WRITE;
> > +    *nshared = 0;
> 
> 0 for shared is probably enough to ward every other access off, but
> maybe we should still pro forma request consistent read access...?

Makes sense, yes.

But you missed the real bug I hid there for you:

qemu-system-x86_64: block.c:1530: bdrv_check_update_perm: Assertion
`new_shared_perm & BLK_PERM_WRITE_UNCHANGED' failed.

Kevin

> Max
> 
> > +}
> > +
> >  static void vvfat_close(BlockDriverState *bs)
> >  {
> >      BDRVVVFATState *s = bs->opaque;
> > @@ -3077,6 +3089,7 @@ static BlockDriver bdrv_vvfat = {
> >      .bdrv_file_open         = vvfat_open,
> >      .bdrv_refresh_limits    = vvfat_refresh_limits,
> >      .bdrv_close             = vvfat_close,
> > +    .bdrv_child_perm        = vvfat_child_perm,
> >  
> >      .bdrv_co_preadv         = vvfat_co_preadv,
> >      .bdrv_co_pwritev        = vvfat_co_pwritev,
> > 
> 
>

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