block: move block exports to libblockdev

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.
Since bdrv_close_all() (libblock) calls blk_exp_close_all()
(libblockdev) a stub function is required..

Make qemu-nbd.c use signal handling utility functions instead of
duplicating the code. This helps because os-posix.c is in libblockdev
and it depends on a qemu_system_killed() symbol that qemu-nbd.c lacks.
Once we use the signal handling utility functions we also end up
providing the necessary symbol.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20200929125516.186715-4-stefanha@redhat.com
[Fixed s/ndb/nbd/ typo in commit description as suggested by Eric Blake
--Stefan]
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/export/meson.build

@@ -1,2 +1,2 @@
-block_ss.add(files('export.c'))
+blockdev_ss.add(files('export.c'))
-block_ss.add(when: ['CONFIG_LINUX', 'CONFIG_VHOST_USER'], if_true: files('vhost-user-blk-server.c'))
+blockdev_ss.add(when: ['CONFIG_LINUX', 'CONFIG_VHOST_USER'], if_true: files('vhost-user-blk-server.c'))

meson.build

@@ -1443,7 +1443,6 @@ subdir('dump')
 
 block_ss.add(files(
   'block.c',
-  'blockdev-nbd.c',
   'blockjob.c',
   'job.c',
   'qemu-io-cmds.c',
@@ -1456,6 +1455,7 @@ subdir('block')
 
 blockdev_ss.add(files(
   'blockdev.c',
+  'blockdev-nbd.c',
   'iothread.c',
   'job-qmp.c',
 ))
@@ -1832,7 +1832,7 @@ 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')

nbd/meson.build

@@ -1,5 +1,7 @@
 block_ss.add(files(
   'client.c',
   'common.c',
+))
+blockdev_ss.add(files(
   'server.c',
 ))

qemu-nbd.c

@@ -25,6 +25,7 @@
 #include "qapi/error.h"
 #include "qemu/cutils.h"
 #include "sysemu/block-backend.h"
+#include "sysemu/runstate.h" /* for qemu_system_killed() prototype */
 #include "block/block_int.h"
 #include "block/nbd.h"
 #include "qemu/main-loop.h"
@@ -155,7 +156,11 @@ QEMU_COPYRIGHT "\n"
 }
 
 #ifdef CONFIG_POSIX
-static void termsig_handler(int signum)
+/*
+ * The client thread uses SIGTERM to interrupt the server.  A signal
+ * handler ensures that "qemu-nbd -v -c" exits with a nice status code.
+ */
+void qemu_system_killed(int signum, pid_t pid)
 {
     qatomic_cmpxchg(&state, RUNNING, TERMINATE);
     qemu_notify_event();
@@ -582,18 +587,8 @@ int main(int argc, char **argv)
     BlockExportOptions *export_opts;
 
 #ifdef CONFIG_POSIX
-    /*
+    os_setup_early_signal_handling();
-     * Exit gracefully on various signals, which includes SIGTERM used
+    os_setup_signal_handling();
-     * by 'qemu-nbd -v -c'.
-     */
-    struct sigaction sa_sigterm;
-    memset(&sa_sigterm, 0, sizeof(sa_sigterm));
-    sa_sigterm.sa_handler = termsig_handler;
-    sigaction(SIGTERM, &sa_sigterm, NULL);
-    sigaction(SIGINT, &sa_sigterm, NULL);
-    sigaction(SIGHUP, &sa_sigterm, NULL);
-
-    signal(SIGPIPE, SIG_IGN);
 #endif
 
     socket_init();

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)
+{
+}

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('cmos.c'))