vfio/migration: Add a note about migration rate limiting

VFIO migration buffer size is currently limited to 1MB. Therefore, there
is no need to check if migration rate exceeded, as in the worst case it
will exceed by only 1MB.

However, if the buffer size is later changed to a bigger value,
vfio_save_iterate() should enforce migration rate (similar to migration
RAM code).

Add a note about this in vfio_save_iterate() to serve as a reminder.

Suggested-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240304105339.20713-4-avihaih@nvidia.com
Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 0af783a5892b3c21ab7d8d68457ae066e0dd75fb..f82dcabc49a489894817b2102a14dd5d78c29438 100644 (file)
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -505,6 +505,12 @@ static bool vfio_is_active_iterate(void *opaque)
     return vfio_device_state_is_precopy(vbasedev);
 }
 
+/*
+ * Note about migration rate limiting: VFIO migration buffer size is currently
+ * limited to 1MB, so there is no need to check if migration rate exceeded (as
+ * in the worst case it will exceed by 1MB). However, if the buffer size is
+ * later changed to a bigger value, migration rate should be enforced here.
+ */
 static int vfio_save_iterate(QEMUFile *f, void *opaque)
 {
     VFIODevice *vbasedev = opaque;