[PATCH V8 08/39] cpr: blockers

[Steve Sistare]

Add an interface to register a blocker for cpr-save for one or more modes.
Devices and options that do not support a cpr mode can register a blocker,
and cpr-save will fail with a descriptive error message.  Conversely, if
such a device is deleted and un-registers its blocker, cpr will be allowed
again.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 MAINTAINERS             |  1 +
 include/migration/cpr.h |  6 ++++
 migration/cpr.c         | 79 +++++++++++++++++++++++++++++++++++++++++++++++++
 stubs/cpr.c             | 23 ++++++++++++++
 stubs/meson.build       |  1 +
 5 files changed, 110 insertions(+)
 create mode 100644 stubs/cpr.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 9273891..1e4e72f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3159,6 +3159,7 @@ S: Maintained
 F: include/migration/cpr.h
 F: migration/cpr.c
 F: qapi/cpr.json
+F: stubs/cpr.c
 
 Record/replay
 M: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
diff --git a/include/migration/cpr.h b/include/migration/cpr.h
index 1b6c82f..dfe5a1d 100644
--- a/include/migration/cpr.h
+++ b/include/migration/cpr.h
@@ -13,4 +13,10 @@
 void cpr_set_mode(CprMode mode);
 CprMode cpr_get_mode(void);
 
+#define CPR_MODE_ALL CPR_MODE__MAX
+
+int cpr_add_blocker(Error **reasonp, Error **errp, CprMode mode, ...);
+int cpr_add_blocker_str(const char *reason, Error **errp, CprMode mode, ...);
+void cpr_del_blocker(Error **reasonp);
+
 #endif
diff --git a/migration/cpr.c b/migration/cpr.c
index 24b0bcc..c1da784 100644
--- a/migration/cpr.c
+++ b/migration/cpr.c
@@ -29,12 +29,91 @@ void cpr_set_mode(CprMode mode)
     cpr_mode = mode;
 }
 
+static GSList *cpr_blockers[CPR_MODE__MAX];
+
+/*
+ * Add blocker for each mode in varargs list, or for all modes if CPR_MODE_ALL
+ * is specified.  Caller terminates the list with 0 or CPR_MODE_ALL.  This
+ * function takes ownership of *reasonp, and frees it on error, or in
+ * cpr_del_blocker.  errp is set in a later patch.
+ */
+int cpr_add_blocker(Error **reasonp, Error **errp, CprMode mode, ...)
+{
+    int modes = 0;
+    va_list ap;
+    ERRP_GUARD();
+
+    va_start(ap, mode);
+    while (mode != CPR_MODE_NONE && mode != CPR_MODE_ALL) {
+        assert(mode > CPR_MODE_NONE && mode < CPR_MODE__MAX);
+        modes |= BIT(mode);
+        mode = va_arg(ap, CprMode);
+    }
+    va_end(ap);
+    if (mode == CPR_MODE_ALL) {
+        modes = BIT(CPR_MODE__MAX) - 1;
+    }
+
+    for (mode = 0; mode < CPR_MODE__MAX; mode++) {
+        if (modes & BIT(mode)) {
+            cpr_blockers[mode] = g_slist_prepend(cpr_blockers[mode], *reasonp);
+        }
+    }
+    return 0;
+}
+
+/*
+ * Delete the blocker from all modes it is associated with.
+ */
+void cpr_del_blocker(Error **reasonp)
+{
+    CprMode mode;
+
+    if (*reasonp) {
+        for (mode = 0; mode < CPR_MODE__MAX; mode++) {
+            cpr_blockers[mode] = g_slist_remove(cpr_blockers[mode], *reasonp);
+        }
+        error_free(*reasonp);
+        *reasonp = NULL;
+    }
+}
+
+/*
+ * Add a blocker which will not be deleted.  Simpler for some callers.
+ */
+int cpr_add_blocker_str(const char *msg, Error **errp, CprMode mode, ...)
+{
+    int ret;
+    va_list ap;
+    Error *reason = NULL;
+
+    error_setg(&reason, "%s", msg);
+    va_start(ap, mode);
+    ret = cpr_add_blocker(&reason, errp, mode, ap);
+    va_end(ap);
+    return ret;
+}
+
+static bool cpr_is_blocked(Error **errp, CprMode mode)
+{
+    if (cpr_blockers[mode]) {
+        error_propagate(errp, error_copy(cpr_blockers[mode]->data));
+        return true;
+    }
+
+    return false;
+}
+
 void qmp_cpr_save(const char *filename, CprMode mode, Error **errp)
 {
     int ret;
     QEMUFile *f;
     int saved_vm_running = runstate_is_running();
 
+    if (cpr_is_blocked(errp, mode)) {
+        return;
+    }
+
     if (global_state_store()) {
         error_setg(errp, "Error saving global state");
         return;
diff --git a/stubs/cpr.c b/stubs/cpr.c
new file mode 100644
index 0000000..06a9a1c
--- /dev/null
+++ b/stubs/cpr.c
@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2022 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "migration/cpr.h"
+
+int cpr_add_blocker(Error **reasonp, Error **errp, CprMode mode, ...)
+{
+    return 0;
+}
+
+int cpr_add_blocker_str(const char *reason, Error **errp, CprMode mode, ...)
+{
+    return 0;
+}
+
+void cpr_del_blocker(Error **reasonp)
+{
+}
diff --git a/stubs/meson.build b/stubs/meson.build
index 6f80fec..0d7565b 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -4,6 +4,7 @@ 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'))
+stub_ss.add(files('cpr.c'))
 stub_ss.add(files('cpu-get-clock.c'))
 stub_ss.add(files('cpus-get-virtual-clock.c'))
 stub_ss.add(files('qemu-timer-notify-cb.c'))
-- 
1.8.3.1