Block exports are used by softmmu, qemu-storage-daemon, and qemu-nbd.
They are not used by other programs and are not otherwise needed in
libblock.

Undo the recent move of blockdev-nbd.c from blockdev_ss into block_ss.
Two stubs are required to support this:
1. bdrv_close_all() (libblock) calls blk_exp_close_all() (libblockdev).
2. qemu_system_killed() is called by os-posix.c (libblockdev) and not
   implemented in qemu-nbd.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 stubs/blk-exp-close-all.c  |  7 +++++++
 stubs/qemu-system-killed.c | 10 ++++++++++
 block/export/meson.build   |  4 ++--
 meson.build                |  4 ++--
 nbd/meson.build            |  2 ++
 stubs/meson.build          |  2 ++
 6 files changed, 25 insertions(+), 4 deletions(-)
 create mode 100644 stubs/blk-exp-close-all.c
 create mode 100644 stubs/qemu-system-killed.c

diff --git a/stubs/blk-exp-close-all.c b/stubs/blk-exp-close-all.c
new file mode 100644
index 0000000000..1c71316763
--- /dev/null
+++ b/stubs/blk-exp-close-all.c
@@ -0,0 +1,7 @@
+#include "qemu/osdep.h"
+#include "block/export.h"
+
+/* Only used in programs that support block exports (libblockdev.fa) */
+void blk_exp_close_all(void)
+{
+}
diff --git a/stubs/qemu-system-killed.c b/stubs/qemu-system-killed.c
new file mode 100644
index 0000000000..9af131917b
--- /dev/null
+++ b/stubs/qemu-system-killed.c
@@ -0,0 +1,10 @@
+#include "qemu/osdep.h"
+#include "sysemu/runstate.h"
+
+/*
+ * This function is needed by os-posix.c but only implemented by softmmu and
+ * qemu-storage-daemon. Other programs may have no need for it.
+ */
+void qemu_system_killed(int signal, pid_t pid)
+{
+}
diff --git a/block/export/meson.build b/block/export/meson.build
index 469a7aa0f5..a2772a0dce 100644
--- a/block/export/meson.build
+++ b/block/export/meson.build
@@ -1,2 +1,2 @@
-block_ss.add(files('export.c'))
-block_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user-blk-server.c'))
+blockdev_ss.add(files('export.c'))
+blockdev_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user-blk-server.c'))
diff --git a/meson.build b/meson.build
index 18d689b423..0e9528adab 100644
--- a/meson.build
+++ b/meson.build
@@ -835,7 +835,6 @@ subdir('dump')
 
 block_ss.add(files(
   'block.c',
-  'blockdev-nbd.c',
   'blockjob.c',
   'job.c',
   'qemu-io-cmds.c',
@@ -848,6 +847,7 @@ subdir('block')
 
 blockdev_ss.add(files(
   'blockdev.c',
+  'blockdev-nbd.c',
   'iothread.c',
   'job-qmp.c',
 ))
@@ -1171,7 +1171,7 @@ if have_tools
   qemu_io = executable('qemu-io', files('qemu-io.c'),
              dependencies: [block, qemuutil], install: true)
   qemu_nbd = executable('qemu-nbd', files('qemu-nbd.c'),
-               dependencies: [block, qemuutil], install: true)
+               dependencies: [blockdev, qemuutil], install: true)
 
   subdir('storage-daemon')
   subdir('contrib/rdmacm-mux')
diff --git a/nbd/meson.build b/nbd/meson.build
index 0c00a776d3..2baaa36948 100644
--- a/nbd/meson.build
+++ b/nbd/meson.build
@@ -1,5 +1,7 @@
 block_ss.add(files(
   'client.c',
   'common.c',
+))
+blockdev_ss.add(files(
   'server.c',
 ))
diff --git a/stubs/meson.build b/stubs/meson.build
index e0b322bc28..60234571b1 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -1,6 +1,7 @@
 stub_ss.add(files('arch_type.c'))
 stub_ss.add(files('bdrv-next-monitor-owned.c'))
 stub_ss.add(files('blk-commit-all.c'))
+stub_ss.add(files('blk-exp-close-all.c'))
 stub_ss.add(files('blockdev-close-all-bdrv-states.c'))
 stub_ss.add(files('change-state-handler.c'))
 stub_ss.add(files('clock-warp.c'))
@@ -25,6 +26,7 @@ stub_ss.add(files('monitor.c'))
 stub_ss.add(files('monitor-core.c'))
 stub_ss.add(files('pci-bus.c'))
 stub_ss.add(files('pci-host-piix.c'))
+stub_ss.add(files('qemu-system-killed.c'))
 stub_ss.add(files('qemu-timer-notify-cb.c'))
 stub_ss.add(files('qmp_memory_device.c'))
 stub_ss.add(files('qtest.c'))
-- 
2.26.2

On 25/09/20 15:42, Stefan Hajnoczi wrote:
> Block exports are used by softmmu, qemu-storage-daemon, and qemu-nbd.
> They are not used by other programs and are not otherwise needed in
> libblock.
> 
> Undo the recent move of blockdev-nbd.c from blockdev_ss into block_ss.
> Two stubs are required to support this:
> 1. bdrv_close_all() (libblock) calls blk_exp_close_all() (libblockdev).
> 2. qemu_system_killed() is called by os-posix.c (libblockdev) and not
>    implemented in qemu-nbd.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Another possibility is to call os_setup_signal_handling in qemu-nbd.c
where we currently set the SIGTERM handler.  The existing
termsig_handler can be repurposed as qemu_system_killed.

Paolo


> ---
>  stubs/blk-exp-close-all.c  |  7 +++++++
>  stubs/qemu-system-killed.c | 10 ++++++++++
>  block/export/meson.build   |  4 ++--
>  meson.build                |  4 ++--
>  nbd/meson.build            |  2 ++
>  stubs/meson.build          |  2 ++
>  6 files changed, 25 insertions(+), 4 deletions(-)
>  create mode 100644 stubs/blk-exp-close-all.c
>  create mode 100644 stubs/qemu-system-killed.c
> 
> diff --git a/stubs/blk-exp-close-all.c b/stubs/blk-exp-close-all.c
> new file mode 100644
> index 0000000000..1c71316763
> --- /dev/null
> +++ b/stubs/blk-exp-close-all.c
> @@ -0,0 +1,7 @@
> +#include "qemu/osdep.h"
> +#include "block/export.h"
> +
> +/* Only used in programs that support block exports (libblockdev.fa) */
> +void blk_exp_close_all(void)
> +{
> +}
> diff --git a/stubs/qemu-system-killed.c b/stubs/qemu-system-killed.c
> new file mode 100644
> index 0000000000..9af131917b
> --- /dev/null
> +++ b/stubs/qemu-system-killed.c
> @@ -0,0 +1,10 @@
> +#include "qemu/osdep.h"
> +#include "sysemu/runstate.h"
> +
> +/*
> + * This function is needed by os-posix.c but only implemented by softmmu and
> + * qemu-storage-daemon. Other programs may have no need for it.
> + */
> +void qemu_system_killed(int signal, pid_t pid)
> +{
> +}
> diff --git a/block/export/meson.build b/block/export/meson.build
> index 469a7aa0f5..a2772a0dce 100644
> --- a/block/export/meson.build
> +++ b/block/export/meson.build
> @@ -1,2 +1,2 @@
> -block_ss.add(files('export.c'))
> -block_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user-blk-server.c'))
> +blockdev_ss.add(files('export.c'))
> +blockdev_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user-blk-server.c'))
> diff --git a/meson.build b/meson.build
> index 18d689b423..0e9528adab 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -835,7 +835,6 @@ subdir('dump')
>  
>  block_ss.add(files(
>    'block.c',
> -  'blockdev-nbd.c',
>    'blockjob.c',
>    'job.c',
>    'qemu-io-cmds.c',
> @@ -848,6 +847,7 @@ subdir('block')
>  
>  blockdev_ss.add(files(
>    'blockdev.c',
> +  'blockdev-nbd.c',
>    'iothread.c',
>    'job-qmp.c',
>  ))
> @@ -1171,7 +1171,7 @@ if have_tools
>    qemu_io = executable('qemu-io', files('qemu-io.c'),
>               dependencies: [block, qemuutil], install: true)
>    qemu_nbd = executable('qemu-nbd', files('qemu-nbd.c'),
> -               dependencies: [block, qemuutil], install: true)
> +               dependencies: [blockdev, qemuutil], install: true)
>  
>    subdir('storage-daemon')
>    subdir('contrib/rdmacm-mux')
> diff --git a/nbd/meson.build b/nbd/meson.build
> index 0c00a776d3..2baaa36948 100644
> --- a/nbd/meson.build
> +++ b/nbd/meson.build
> @@ -1,5 +1,7 @@
>  block_ss.add(files(
>    'client.c',
>    'common.c',
> +))
> +blockdev_ss.add(files(
>    'server.c',
>  ))
> diff --git a/stubs/meson.build b/stubs/meson.build
> index e0b322bc28..60234571b1 100644
> --- a/stubs/meson.build
> +++ b/stubs/meson.build
> @@ -1,6 +1,7 @@
>  stub_ss.add(files('arch_type.c'))
>  stub_ss.add(files('bdrv-next-monitor-owned.c'))
>  stub_ss.add(files('blk-commit-all.c'))
> +stub_ss.add(files('blk-exp-close-all.c'))
>  stub_ss.add(files('blockdev-close-all-bdrv-states.c'))
>  stub_ss.add(files('change-state-handler.c'))
>  stub_ss.add(files('clock-warp.c'))
> @@ -25,6 +26,7 @@ stub_ss.add(files('monitor.c'))
>  stub_ss.add(files('monitor-core.c'))
>  stub_ss.add(files('pci-bus.c'))
>  stub_ss.add(files('pci-host-piix.c'))
> +stub_ss.add(files('qemu-system-killed.c'))
>  stub_ss.add(files('qemu-timer-notify-cb.c'))
>  stub_ss.add(files('qmp_memory_device.c'))
>  stub_ss.add(files('qtest.c'))
> 

On Fri, Sep 25, 2020 at 04:11:54PM +0200, Paolo Bonzini wrote:
> On 25/09/20 15:42, Stefan Hajnoczi wrote:
> > Block exports are used by softmmu, qemu-storage-daemon, and qemu-nbd.
> > They are not used by other programs and are not otherwise needed in
> > libblock.
> > 
> > Undo the recent move of blockdev-nbd.c from blockdev_ss into block_ss.
> > Two stubs are required to support this:
> > 1. bdrv_close_all() (libblock) calls blk_exp_close_all() (libblockdev).
> > 2. qemu_system_killed() is called by os-posix.c (libblockdev) and not
> >    implemented in qemu-nbd.
> > 
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> Another possibility is to call os_setup_signal_handling in qemu-nbd.c
> where we currently set the SIGTERM handler.  The existing
> termsig_handler can be repurposed as qemu_system_killed.

That is nicer. Will fix in v2.

Stefan