Re: [Qemu-devel] [PATCH] quorum: Only compile when supported

[Fam Zheng <famz@redhat.com>]

On Tue, 07/05 09:45, Daniel P. Berrange wrote:
> On Tue, Jun 28, 2016 at 09:47:47AM +0800, Fam Zheng wrote:
> > This was the only exceptional module init function that does something
> > else than a simple list of bdrv_register() calls, in all the block
> > drivers.
> > 
> > The qcrypto_hash_supports is actually a static check, determined at
> > compile time.  Follow the block-job-$(CONFIG_FOO) convention for
> > consistency.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> 
> The point of using qcrypto_hash_supports() is that it isolates the
> block code Makefile rules from the details of the current specific
> impl of the hash APIs in QEMU. As a prime example of why this is
> important, try rebasing to GIT master, and you'll find we no longer
> use gnutls for the hash APIs. We choose between libgcrypt, nettle
> or a empty stub for hash impls now. I think it is a backwards step
> to add back these makefile conditionals

I don't want to spoil the isolation, but I think it's also worth to keep the
reasoning of whether a driver is supported as simple as possible. In other
words, if it's determined at configure time, there is no reason to use a
runtime check, right?

Fam

> 
> > ---
> >  block/Makefile.objs | 2 +-
> >  block/quorum.c      | 4 ----
> >  2 files changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/block/Makefile.objs b/block/Makefile.objs
> > index 44a5416..c87d605 100644
> > --- a/block/Makefile.objs
> > +++ b/block/Makefile.objs
> > @@ -3,7 +3,7 @@ block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o qcow2-c
> >  block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
> >  block-obj-y += qed-check.o
> >  block-obj-$(CONFIG_VHDX) += vhdx.o vhdx-endian.o vhdx-log.o
> > -block-obj-y += quorum.o
> > +block-obj-$(CONFIG_GNUTLS_HASH) += quorum.o
> >  block-obj-y += parallels.o blkdebug.o blkverify.o blkreplay.o
> >  block-obj-y += block-backend.o snapshot.o qapi.o
> >  block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
> > diff --git a/block/quorum.c b/block/quorum.c
> > index 331b726..18fbed8 100644
> > --- a/block/quorum.c
> > +++ b/block/quorum.c
> > @@ -1113,10 +1113,6 @@ static BlockDriver bdrv_quorum = {
> >  
> >  static void bdrv_quorum_init(void)
> >  {
> > -    if (!qcrypto_hash_supports(QCRYPTO_HASH_ALG_SHA256)) {
> > -        /* SHA256 hash support is required for quorum device */
> > -        return;
> > -    }
> >      bdrv_register(&bdrv_quorum);
> >  }
> >  
> > -- 
> > 2.9.0
> > 
> > 
> 
> Regards,
> Daniel
> -- 
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