migration: cpr helpers

Add the cpr_incoming_needed, cpr_open_fd, and cpr_resave_fd helpers,
for use when adding cpr support for vfio and iommufd.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/1749569991-25171-2-git-send-email-steven.sistare@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

include/migration/cpr.h

@@ -18,6 +18,9 @@
 void cpr_save_fd(const char *name, int id, int fd);
 void cpr_delete_fd(const char *name, int id);
 int cpr_find_fd(const char *name, int id);
+void cpr_resave_fd(const char *name, int id, int fd);
+int cpr_open_fd(const char *path, int flags, const char *name, int id,
+                Error **errp);
 
 MigMode cpr_get_incoming_mode(void);
 void cpr_set_incoming_mode(MigMode mode);
@@ -28,6 +31,8 @@ int cpr_state_load(MigrationChannel *channel, Error **errp);
 void cpr_state_close(void);
 struct QIOChannel *cpr_state_ioc(void);
 
+bool cpr_incoming_needed(void *opaque);
+
 QEMUFile *cpr_transfer_output(MigrationChannel *channel, Error **errp);
 QEMUFile *cpr_transfer_input(MigrationChannel *channel, Error **errp);
 

migration/cpr.c

@@ -95,6 +95,36 @@ int cpr_find_fd(const char *name, int id)
     trace_cpr_find_fd(name, id, fd);
     return fd;
 }
+
+void cpr_resave_fd(const char *name, int id, int fd)
+{
+    CprFd *elem = find_fd(&cpr_state.fds, name, id);
+    int old_fd = elem ? elem->fd : -1;
+
+    if (old_fd < 0) {
+        cpr_save_fd(name, id, fd);
+    } else if (old_fd != fd) {
+        error_setg(&error_fatal,
+                   "internal error: cpr fd '%s' id %d value %d "
+                   "already saved with a different value %d",
+                   name, id, fd, old_fd);
+    }
+}
+
+int cpr_open_fd(const char *path, int flags, const char *name, int id,
+                Error **errp)
+{
+    int fd = cpr_find_fd(name, id);
+
+    if (fd < 0) {
+        fd = qemu_open(path, flags, errp);
+        if (fd >= 0) {
+            cpr_save_fd(name, id, fd);
+        }
+    }
+    return fd;
+}
+
 /*************************************************************************/
 #define CPR_STATE "CprState"
 
@@ -228,3 +258,9 @@ void cpr_state_close(void)
         cpr_state_file = NULL;
     }
 }
+
+bool cpr_incoming_needed(void *opaque)
+{
+    MigMode mode = migrate_mode();
+    return mode == MIG_MODE_CPR_TRANSFER;
+}