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

[Eric Blake <eblake@redhat.com>]

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.

Reviewed-by: Eric Blake <eblake@redhat.com>

I'm happy to queue this series through my NBD tree.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org