Add a new writeable features config space field, which allows the guest to communicate features it wants enabled/disabled at runtime. The only feature defined so far is the status of the volatile write cache.
Also rename the virtio_blk_update_config to virtio_blk_get_config to fit the method naming scheme. Signed-off-by: Christoph Hellwig <h...@lst.de> Index: qemu/hw/virtio-blk.c =================================================================== --- qemu.orig/hw/virtio-blk.c 2011-03-15 13:07:10.093633862 +0100 +++ qemu/hw/virtio-blk.c 2011-03-15 13:07:54.108135875 +0100 @@ -434,7 +434,7 @@ static void virtio_blk_reset(VirtIODevic /* coalesce internal state, copy to pci i/o region 0 */ -static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config) +static void virtio_blk_get_config(VirtIODevice *vdev, uint8_t *config) { VirtIOBlock *s = to_virtio_blk(vdev); struct virtio_blk_config blkcfg; @@ -455,9 +455,26 @@ static void virtio_blk_update_config(Vir blkcfg.alignment_offset = 0; blkcfg.min_io_size = s->conf->min_io_size / blkcfg.blk_size; blkcfg.opt_io_size = s->conf->opt_io_size / blkcfg.blk_size; + if (bdrv_enable_write_cache(s->bs)) + blkcfg.features |= VIRTIO_BLK_RT_WCE; memcpy(config, &blkcfg, sizeof(struct virtio_blk_config)); } +static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config) +{ + VirtIOBlock *s = to_virtio_blk(vdev); + struct virtio_blk_config blkcfg; + bool enable = false; + + memcpy(&blkcfg, config, sizeof(blkcfg)); + + if (blkcfg.features & VIRTIO_BLK_RT_WCE) + enable = true; + + /* no error reporting, needs to be checked by a config re-read */ + bdrv_change_cache(s->bs, enable); +} + static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features) { VirtIOBlock *s = to_virtio_blk(vdev); @@ -466,6 +483,7 @@ static uint32_t virtio_blk_get_features( features |= (1 << VIRTIO_BLK_F_GEOMETRY); features |= (1 << VIRTIO_BLK_F_TOPOLOGY); features |= (1 << VIRTIO_BLK_F_BLK_SIZE); + features |= (1 << VIRTIO_BLK_F_DYNAMIC); if (bdrv_enable_write_cache(s->bs)) features |= (1 << VIRTIO_BLK_F_WCACHE); @@ -543,7 +561,8 @@ VirtIODevice *virtio_blk_init(DeviceStat sizeof(struct virtio_blk_config), sizeof(VirtIOBlock)); - s->vdev.get_config = virtio_blk_update_config; + s->vdev.get_config = virtio_blk_get_config; + s->vdev.set_config = virtio_blk_set_config; s->vdev.get_features = virtio_blk_get_features; s->vdev.reset = virtio_blk_reset; s->bs = conf->bs; Index: qemu/hw/virtio-blk.h =================================================================== --- qemu.orig/hw/virtio-blk.h 2011-03-15 13:07:10.109636192 +0100 +++ qemu/hw/virtio-blk.h 2011-03-15 13:07:54.112135546 +0100 @@ -33,6 +33,7 @@ /* #define VIRTIO_BLK_F_IDENTIFY 8 ATA IDENTIFY supported, DEPRECATED */ #define VIRTIO_BLK_F_WCACHE 9 /* write cache enabled */ #define VIRTIO_BLK_F_TOPOLOGY 10 /* Topology information is available */ +#define VIRTIO_BLK_F_DYNAMIC 11 /* Dynamic features field */ struct virtio_blk_config { @@ -47,6 +48,8 @@ struct virtio_blk_config uint8_t alignment_offset; uint16_t min_io_size; uint32_t opt_io_size; + uint32_t features; +#define VIRTIO_BLK_RT_WCE (1 << 0) } __attribute__((packed)); /* These two define direction. */