librados: expose op cancellation through AioCompletion::cancel()

Signed-off-by: Casey Bodley <[email protected]>

Author: cbodley

PendingReleaseNotes

@@ -34,6 +34,8 @@
   (--yes-i-really-mean-it). This has been added as a precaution to tell the
   users that modifying "max_mds" may not help with troubleshooting or recovery
   effort. Instead, it might further destabilize the cluster.
+* RADOS: Added convenience function `librados::AioCompletion::cancel()` with
+  the same behavior as `librados::IoCtx::aio_cancel()`.
 
 * mgr/restful, mgr/zabbix: both modules, already deprecated since 2020, have been
   finally removed. They have not been actively maintenance in the last years,

src/include/rados/librados.hpp

@@ -202,6 +202,9 @@ inline namespace v14_2_0 {
     int set_complete_callback(void *cb_arg, callback_t cb);
     int set_safe_callback(void *cb_arg, callback_t cb)
       __attribute__ ((deprecated));
+    /// Request immediate cancellation with error code -ECANCELED
+    /// if the operation hasn't already completed.
+    int cancel();
     int wait_for_complete();
     int wait_for_safe() __attribute__ ((deprecated));
     int wait_for_complete_and_cb();

src/librados/librados_cxx.cc

@@ -1103,6 +1103,14 @@ void librados::AioCompletion::release()
   delete this;
 }
 
+int librados::AioCompletion::cancel()
+{
+  if (!pc->io) {
+    return 0; // no operation was started
+  }
+  return pc->io->aio_cancel(pc);
+}
+
 ///////////////////////////// IoCtx //////////////////////////////
 librados::IoCtx::IoCtx() : io_ctx_impl(NULL)
 {