xv6-65oo2/kernel/virtio.h

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//
// virtio device definitions.
// for both the mmio interface, and virtio descriptors.
// only tested with qemu.
// this is the "legacy" virtio interface.
//
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// the virtio spec:
// https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.pdf
//
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// virtio mmio control registers, mapped starting at 0x10001000.
// from qemu virtio_mmio.h
#define VIRTIO_MMIO_MAGIC_VALUE 0x000 // 0x74726976
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#define VIRTIO_MMIO_VERSION 0x004 // version; 1 is legacy
#define VIRTIO_MMIO_DEVICE_ID 0x008 // device type; 1 is net, 2 is disk
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#define VIRTIO_MMIO_VENDOR_ID 0x00c // 0x554d4551
#define VIRTIO_MMIO_DEVICE_FEATURES 0x010
#define VIRTIO_MMIO_DRIVER_FEATURES 0x020
#define VIRTIO_MMIO_GUEST_PAGE_SIZE 0x028 // page size for PFN, write-only
#define VIRTIO_MMIO_QUEUE_SEL 0x030 // select queue, write-only
#define VIRTIO_MMIO_QUEUE_NUM_MAX 0x034 // max size of current queue, read-only
#define VIRTIO_MMIO_QUEUE_NUM 0x038 // size of current queue, write-only
#define VIRTIO_MMIO_QUEUE_ALIGN 0x03c // used ring alignment, write-only
#define VIRTIO_MMIO_QUEUE_PFN 0x040 // physical page number for queue, read/write
#define VIRTIO_MMIO_QUEUE_READY 0x044 // ready bit
#define VIRTIO_MMIO_QUEUE_NOTIFY 0x050 // write-only
#define VIRTIO_MMIO_INTERRUPT_STATUS 0x060 // read-only
#define VIRTIO_MMIO_INTERRUPT_ACK 0x064 // write-only
#define VIRTIO_MMIO_STATUS 0x070 // read/write
// status register bits, from qemu virtio_config.h
#define VIRTIO_CONFIG_S_ACKNOWLEDGE 1
#define VIRTIO_CONFIG_S_DRIVER 2
#define VIRTIO_CONFIG_S_DRIVER_OK 4
#define VIRTIO_CONFIG_S_FEATURES_OK 8
// device feature bits
#define VIRTIO_BLK_F_RO 5 /* Disk is read-only */
#define VIRTIO_BLK_F_SCSI 7 /* Supports scsi command passthru */
#define VIRTIO_BLK_F_CONFIG_WCE 11 /* Writeback mode available in config */
#define VIRTIO_BLK_F_MQ 12 /* support more than one vq */
#define VIRTIO_F_ANY_LAYOUT 27
#define VIRTIO_RING_F_INDIRECT_DESC 28
#define VIRTIO_RING_F_EVENT_IDX 29
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// this many virtio descriptors.
// must be a power of two.
#define NUM 8
// a single descriptor, from the spec.
struct virtq_desc {
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uint64 addr;
uint32 len;
uint16 flags;
uint16 next;
};
#define VRING_DESC_F_NEXT 1 // chained with another descriptor
#define VRING_DESC_F_WRITE 2 // device writes (vs read)
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// the (entire) avail ring, from the spec.
struct virtq_avail {
uint16 flags; // always zero
uint16 idx; // driver will write ring[idx] next
uint16 ring[NUM]; // descriptor numbers of chain heads
uint16 unused;
};
// one entry in the "used" ring, with which the
// device tells the driver about completed requests.
struct virtq_used_elem {
uint32 id; // index of start of completed descriptor chain
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uint32 len;
};
struct virtq_used {
uint16 flags; // always zero
uint16 idx; // device increments when it adds a ring[] entry
struct virtq_used_elem ring[NUM];
};
// these are specific to virtio block devices, e.g. disks,
// described in Section 5.2 of the spec.
#define VIRTIO_BLK_T_IN 0 // read the disk
#define VIRTIO_BLK_T_OUT 1 // write the disk
// the format of the first descriptor in a disk request.
// to be followed by two more descriptors containing
// the block, and a one-byte status.
struct virtio_blk_req {
uint32 type; // VIRTIO_BLK_T_IN or ..._OUT
uint32 reserved;
uint64 sector;
};