[Qemu-devel] [PATCH] eventfd: making it thread safe

[Alexey Kardashevskiy <aik@ozlabs.ru>]

QEMU uses IO handlers to run select() in the main loop.
The handlers list is managed by qemu_set_fd_handler() helper
which works fine when called from the main thread as it is
called not when select() is waiting.

However IO handlers list can be changed in the thread other than
the main one doing os_host_main_loop_wait(), for example, as a result
of a hypercall which changes PCI config space (VFIO on POWER is the case)
and enables/disabled MSI/MSIX which closes/creates eventfd handles.
If the main loop is waiting on such eventfd, it has to be restarted.

The patch adds the qemu_notify_event() call to interrupt select()
and make main_loop() to restart select() with the updated IO
handlers list.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
 iohandler.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/iohandler.c b/iohandler.c
index 3c74de6..dea4355 100644
--- a/iohandler.c
+++ b/iohandler.c
@@ -77,6 +77,7 @@ int qemu_set_fd_handler2(int fd,
         ioh->fd_write = fd_write;
         ioh->opaque = opaque;
         ioh->deleted = 0;
+        qemu_notify_event();
     }
     return 0;
 }
-- 
1.7.10.4