linux-kernel - [PATCH 2/2] virtio: document virtio_config

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Message-Id: <20190103160804.21438-3-cohuck@redhat.com>
Date:   Thu,  3 Jan 2019 17:08:04 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, virtio-dev@...ts.oasis-open.org,
        Wei Wang <wei.w.wang@...el.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: [PATCH 2/2] virtio: document virtio_config_ops restrictions

Some transports (e.g. virtio-ccw) implement virtio operations that
seem to be a simple read/write as something more involved that
cannot be done from an atomic context.

Give at least a hint about that.

Signed-off-by: Cornelia Huck <cohuck@...hat.com>
---
 include/linux/virtio_config.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7087ef946ba7..987b6491b946 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -12,6 +12,11 @@ struct irq_affinity;
 
 /**
  * virtio_config_ops - operations for configuring a virtio device
+ * Note: Do not assume that a transport implements all of the operations
+ *       getting/setting a value as a simple read/write! Generally speaking,
+ *       any of @get/@set, @get_status/@..._status, or @get_features/
+ *       @finalize_features are NOT safe to be called from an atomic
+ *       context.
  * @get: read the value of a configuration field
  *	vdev: the virtio_device
  *	offset: the offset of the configuration field
-- 
2.17.2