Re: [PATCH v2 1/6] virtio_balloon: transitional interface
From: Rusty Russell <hidden>
Date: 2015-04-01 04:20:50
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"Michael S. Tsirkin" [off-list ref] writes:
Virtio 1.0 doesn't include a modern balloon device. But it's not a big change to support a transitional balloon device: this has the advantage of supporting existing drivers, transparently.
You decided to fix the packed struct...
quoted hunk ↗ jump to hunk
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 6a356e3..574267f 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c@@ -77,7 +77,7 @@ struct virtio_balloon { /* Memory statistics */ int need_stats_update; - struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; + struct virtio_balloon_stat_modern stats[VIRTIO_BALLOON_S_NR]; /* To register callback in oom notifier call chain */ struct notifier_block nb;@@ -269,7 +269,11 @@ static void stats_handle_request(struct virtio_balloon *vb) vq = vb->stats_vq; if (!virtqueue_get_buf(vq, &len)) return; - sg_init_one(&sg, vb->stats, sizeof(vb->stats)); + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) + sg_init_one(&sg, vb->stats, sizeof(vb->stats)); + else + sg_init_one(&sg, &vb->stats->tag, sizeof(vb->stats) - + offsetof(typeof(*vb->stats, tag);
This makes it compile, but definitely won't work.
quoted hunk ↗ jump to hunk
virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); virtqueue_kick(vq); }@@ -283,21 +287,30 @@ static void virtballoon_changed(struct virtio_device *vdev) static inline s64 towards_target(struct virtio_balloon *vb) { - __le32 v; s64 target; + u32 num_pages; - virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages, &v); + virtio_cread(vb->vdev, struct virtio_balloon_config, + num_pages, &num_pages); - target = le32_to_cpu(v); + /* Legacy balloon config space is LE, unlike all other devices. */ + if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) + num_pages = le32_to_cpu((__force le32)num_pages); + + target = num_pages; return target - vb->num_pages; } static void update_balloon_size(struct virtio_balloon *vb) { - __le32 actual = cpu_to_le32(vb->num_pages); + u32 actual = vb->num_pages; + + /* Legacy balloon config space is LE, unlike all other devices. */ + if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) + actual = (__force u32)cpu_to_le32(num_pages); - virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual, - &actual); + virtio_cwrite(vb->vdev, struct virtio_balloon_config, + actual, &actual); }
Final line is gratitous reformatting. I would leave the device *exactly* as is, ugly structure packing and all. Cheers, Rusty.