[PULL 1/1] virtio-blk: Respect discard granularity

[Stefan Hajnoczi <stefanha@redhat.com>]

From: Akihiko Odaki <akihiko.odaki@gmail.com>

Report the configured granularity for discard operation to the
guest. If this is not set use the block size.

Since until now we have ignored the configured discard granularity
and always reported the block size, let's add
'report-discard-granularity' property and disable it for older
machine types to avoid migration issues.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210225001239.47046-1-akihiko.odaki@gmail.com>
---
 include/hw/virtio/virtio-blk.h | 1 +
 hw/block/virtio-blk.c          | 8 +++++++-
 hw/core/machine.c              | 1 +
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 214ab74822..29655a406d 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -41,6 +41,7 @@ struct VirtIOBlkConf
     uint16_t num_queues;
     uint16_t queue_size;
     bool seg_max_adjust;
+    bool report_discard_granularity;
     uint32_t max_discard_sectors;
     uint32_t max_write_zeroes_sectors;
     bool x_enable_wce_if_config_wce;
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 3d2072cf75..d28979efb8 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -962,10 +962,14 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
     blkcfg.wce = blk_enable_write_cache(s->blk);
     virtio_stw_p(vdev, &blkcfg.num_queues, s->conf.num_queues);
     if (virtio_has_feature(s->host_features, VIRTIO_BLK_F_DISCARD)) {
+        uint32_t discard_granularity = conf->discard_granularity;
+        if (discard_granularity == -1 || !s->conf.report_discard_granularity) {
+            discard_granularity = blk_size;
+        }
         virtio_stl_p(vdev, &blkcfg.max_discard_sectors,
                      s->conf.max_discard_sectors);
         virtio_stl_p(vdev, &blkcfg.discard_sector_alignment,
-                     blk_size >> BDRV_SECTOR_BITS);
+                     discard_granularity >> BDRV_SECTOR_BITS);
         /*
          * We support only one segment per request since multiple segments
          * are not widely used and there are no userspace APIs that allow
@@ -1299,6 +1303,8 @@ static Property virtio_blk_properties[] = {
                      IOThread *),
     DEFINE_PROP_BIT64("discard", VirtIOBlock, host_features,
                       VIRTIO_BLK_F_DISCARD, true),
+    DEFINE_PROP_BOOL("report-discard-granularity", VirtIOBlock,
+                     conf.report_discard_granularity, true),
     DEFINE_PROP_BIT64("write-zeroes", VirtIOBlock, host_features,
                       VIRTIO_BLK_F_WRITE_ZEROES, true),
     DEFINE_PROP_UINT32("max-discard-sectors", VirtIOBlock,
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 4386f57b5c..4c1a4a4c32 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -39,6 +39,7 @@
 GlobalProperty hw_compat_5_2[] = {
     { "ICH9-LPC", "smm-compat", "on"},
     { "PIIX4_PM", "smm-compat", "on"},
+    { "virtio-blk-device", "report-discard-granularity", "off" },
 };
 const size_t hw_compat_5_2_len = G_N_ELEMENTS(hw_compat_5_2);
 
-- 
2.29.2