Re: [PATCH 2/2] nbd: disable signals and forking on Windows builds

[Daniel P . Berrangé]

On Mon, Aug 24, 2020 at 12:12:53PM -0500, Eric Blake wrote:
> On 8/24/20 12:02 PM, Daniel P. Berrangé wrote:
> > Disabling these parts are sufficient to get the qemu-nbd program
> > compiling in a Windows build.
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >   meson.build |  7 ++-----
> >   qemu-nbd.c  | 10 +++++++++-
> >   2 files changed, 11 insertions(+), 6 deletions(-)
> 
> Feels a bit hacky at what it supports, but certainly better than nothing ;)
> 
> > 
> > diff --git a/meson.build b/meson.build
> > index df5bf728b5..1071871605 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -1074,12 +1074,9 @@ if have_tools
> >                dependencies: [authz, block, crypto, io, qom, qemuutil], 
> > install: true)
> >     qemu_io = executable('qemu-io', files('qemu-io.c'),
> >                dependencies: [block, qemuutil], install: true)
> > -  qemu_block_tools += [qemu_img, qemu_io]
> > -  if targetos == 'linux' or targetos == 'sunos' or targetos.endswith('bsd')
> > -    qemu_nbd = executable('qemu-nbd', files('qemu-nbd.c'),
> > +  qemu_nbd = executable('qemu-nbd', files('qemu-nbd.c'),
> >                  dependencies: [block, qemuutil], install: true)
> 
> Conflicts with this patch:
> https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg05546.html
> 
> but this one gets rid of the need for that one.
> 
> > -    qemu_block_tools += [qemu_nbd]
> > -  endif
> > +  qemu_block_tools += [qemu_img, qemu_io, qemu_nbd]
> >     subdir('storage-daemon')
> >     subdir('contrib/rdmacm-mux')
> > diff --git a/qemu-nbd.c b/qemu-nbd.c
> > index b102874f0f..c6fd6524d3 100644
> > --- a/qemu-nbd.c
> > +++ b/qemu-nbd.c
> > @@ -155,12 +155,13 @@ QEMU_COPYRIGHT "\n"
> >       , name);
> >   }
> > +#ifndef WIN32
> >   static void termsig_handler(int signum)
> >   {
> >       atomic_cmpxchg(&state, RUNNING, TERMINATE);
> >       qemu_notify_event();
> >   }
> > -
> > +#endif
> 
> How does one terminate a long-running server on Windows if there is no
> SIGTERM handler?  I guess Ctrl-C does something, but without the state
> notification from a signal handler, you are getting less-clean shutdowns,
> which may explain the hangs you were seeing in testing?  But incremental
> progress is fine, and I see no reason to not take this patch as-is.

The hangs occurred even with windows client/ native server, just less
frequently so don't think it is related.

Re-reading the code I notice this SIGTERM handler is only there for
the NBD device client thread, so we should skip it if that is not
installed.

Ctrl-C does SIGINT, so that's unrelated to the SIGTERM handler.

> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> I'm happy to queue this series through my NBD tree.

I'll post a v2

Regards,
Daniel
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