[Qemu-devel] Possible regression (was: Re: [PATCH v3 2/3] qom: Avoid unvisited 'id'/'qom-type' in user_creatable_add_opts)

[Richard W.M. Jones]

On Wed, Mar 22, 2017 at 09:45:24AM -0500, Eric Blake wrote:
> A regression in commit 15c2f669e caused us to silently ignore
> excess input to the QemuOpts visitor.  Later, commit ea4641
> accidentally abused that situation, by removing "qom-type" and
> "id" from the corresponding QDict but leaving them defined in
> the QemuOpts, when using the pair of containers to create a
> user-defined object. Note that since we are already traversing
> two separate items (a QDict and a QemuOpts), we are already
> able to flag bogus arguments, as in:
> 
> $ ./x86_64-softmmu/qemu-system-x86_64 -nodefaults -nographic -qmp stdio 
> -object memory-backend-ram,id=mem1,size=4k,bogus=huh
> qemu-system-x86_64: -object memory-backend-ram,id=mem1,size=4k,bogus=huh: 
> Property '.bogus' not found
> 
> So the only real concern is that when we re-enable strict checking
> in the QemuOpts visitor, we do not want to start flagging the two
> leftover keys as unvisited.  Rearrange the code to clean out the
> QemuOpts listing in advance, rather than removing items from the
> QDict.  Since "qom-type" is usually an automatic implicit default,
> we don't have to restore it (this does mean that once instantiated,
> QemuOpts is not necessarily an accurate representation of the
> original command line - but this is not the first place to do that);
> however "id" has to be put back (requiring us to cast away a const).
> 
> [As a side note, hmp_object_add() turns a QDict into a QemuOpts,
> then calls user_creatable_add_opts() which converts QemuOpts into
> a new QDict. There are probably a lot of wasteful conversions like
> this, but cleaning them up is a much bigger task than the immediate
> regression fix.]
> 
> CC: address@hidden
> Signed-off-by: Eric Blake <address@hidden>

This commit causes a problem for libguestfs:

  [02192ms] /home/rjones/d/qemu/x86_64-softmmu/qemu-system-x86_64 \
  [...]
      -object rng-random,filename=/dev/urandom,id=rng0 \
      -device virtio-rng-pci,rng=rng0 \
  [...]
  qemu-system-x86_64: -object rng-random,filename=/dev/urandom,id=rng0: 
Parameter 'qom-type' is missing

(The full log is attached).  I don't know if we should be including
the qom-type parameter here, and if we should what it should be set to.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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log
Description: Text document