xv6-65oo2/kernel/virtio_disk.c

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//
// driver for qemu's virtio disk device.
// uses qemu's mmio interface to virtio.
// qemu presents a "legacy" virtio interface.
//
// qemu ... -drive file=fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0
//
#include "types.h"
#include "riscv.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "fs.h"
#include "buf.h"
#include "virtio.h"
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// the address of virtio mmio register r.
#define R(r) ((volatile uint32 *)(VIRTIO0 + (r)))
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struct spinlock vdisk_lock;
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// memory for virtio descriptors &c for queue 0.
// this is a global instead of allocated because it has
// to be multiple contiguous pages, which kalloc()
// doesn't support.
__attribute__ ((aligned (PGSIZE)))
static char pages[2*PGSIZE];
static struct VRingDesc *desc;
static uint16 *avail;
static struct UsedArea *used;
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// our own book-keeping.
static char free[NUM]; // is a descriptor free?
static uint16 used_idx; // we've looked this far in used[2..NUM].
// track info about in-flight operations,
// for use when completion interrupt arrives.
// indexed by first descriptor index of chain.
static struct {
struct buf *b;
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char status;
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} info[NUM];
void
virtio_disk_init(void)
{
uint32 status = 0;
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initlock(&vdisk_lock, "virtio_disk");
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if(*R(VIRTIO_MMIO_MAGIC_VALUE) != 0x74726976 ||
*R(VIRTIO_MMIO_VERSION) != 1 ||
*R(VIRTIO_MMIO_DEVICE_ID) != 2 ||
*R(VIRTIO_MMIO_VENDOR_ID) != 0x554d4551){
panic("could not find virtio disk");
}
status |= VIRTIO_CONFIG_S_ACKNOWLEDGE;
*R(VIRTIO_MMIO_STATUS) = status;
status |= VIRTIO_CONFIG_S_DRIVER;
*R(VIRTIO_MMIO_STATUS) = status;
// negotiate features
uint64 features = *R(VIRTIO_MMIO_DEVICE_FEATURES);
features &= ~(1 << VIRTIO_BLK_F_RO);
features &= ~(1 << VIRTIO_BLK_F_SCSI);
features &= ~(1 << VIRTIO_BLK_F_CONFIG_WCE);
features &= ~(1 << VIRTIO_BLK_F_MQ);
features &= ~(1 << VIRTIO_F_ANY_LAYOUT);
features &= ~(1 << VIRTIO_RING_F_EVENT_IDX);
features &= ~(1 << VIRTIO_RING_F_INDIRECT_DESC);
*R(VIRTIO_MMIO_DRIVER_FEATURES) = features;
// tell device that feature negotiation is complete.
status |= VIRTIO_CONFIG_S_FEATURES_OK;
*R(VIRTIO_MMIO_STATUS) = status;
// tell device we're completely ready.
status |= VIRTIO_CONFIG_S_DRIVER_OK;
*R(VIRTIO_MMIO_STATUS) = status;
*R(VIRTIO_MMIO_GUEST_PAGE_SIZE) = PGSIZE;
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// initialize queue 0.
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*R(VIRTIO_MMIO_QUEUE_SEL) = 0;
uint32 max = *R(VIRTIO_MMIO_QUEUE_NUM_MAX);
if(max == 0)
panic("virtio disk has no queue 0");
if(max < NUM)
panic("virtio disk max queue too short");
*R(VIRTIO_MMIO_QUEUE_NUM) = NUM;
memset(pages, 0, sizeof(pages));
*R(VIRTIO_MMIO_QUEUE_PFN) = ((uint64)pages) >> PGSHIFT;
// desc = pages -- num * VRingDesc
// avail = pages + 0x40 -- 2 * uint16, then num * uint16
// used = pages + 4096 -- 2 * uint16, then num * vRingUsedElem
desc = (struct VRingDesc *) pages;
avail = (uint16*)(((char*)desc) + NUM*sizeof(struct VRingDesc));
used = (struct UsedArea *) (pages + PGSIZE);
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for(int i = 0; i < NUM; i++)
free[i] = 1;
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// plic.c and trap.c arrange for interrupts from VIRTIO0_IRQ.
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}
// find a free descriptor, mark it non-free, return its index.
static int
alloc_desc()
{
for(int i = 0; i < NUM; i++){
if(free[i]){
free[i] = 0;
return i;
}
}
return -1;
}
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// mark a descriptor as free.
static void
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free_desc(int i)
{
if(i >= NUM)
panic("virtio_disk_intr 1");
if(free[i])
panic("virtio_disk_intr 2");
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desc[i].addr = 0;
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free[i] = 1;
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wakeup(&free[0]);
}
// free a chain of descriptors.
static void
free_chain(int i)
{
while(1){
free_desc(i);
if(desc[i].flags & VRING_DESC_F_NEXT)
i = desc[i].next;
else
break;
}
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}
static int
alloc3_desc(int *idx)
{
for(int i = 0; i < 3; i++){
idx[i] = alloc_desc();
if(idx[i] < 0){
for(int j = 0; j < i; j++)
free_desc(idx[j]);
return -1;
}
}
return 0;
}
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void
virtio_disk_rw(struct buf *b)
{
uint64 sector = b->blockno * (BSIZE / 512);
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acquire(&vdisk_lock);
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// the spec says that legacy block operations use three
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// descriptors: one for type/reserved/sector, one for
// the data, one for a 1-byte status result.
// allocate the three descriptors.
int idx[3];
while(1){
if(alloc3_desc(idx) == 0) {
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break;
}
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sleep(&free[0], &vdisk_lock);
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}
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// format the three descriptors.
// qemu's virtio-blk.c reads them.
struct virtio_blk_outhdr {
uint32 type;
uint32 reserved;
uint64 sector;
} buf0;
if(b->flags & B_DIRTY)
buf0.type = VIRTIO_BLK_T_OUT; // write the disk
else
buf0.type = VIRTIO_BLK_T_IN; // read the disk
buf0.reserved = 0;
buf0.sector = sector;
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// buf0 is on a kernel stack, which is not direct mapped,
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// thus the call to kvmpa().
desc[idx[0]].addr = (uint64) kvmpa((uint64) &buf0);
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desc[idx[0]].len = sizeof(buf0);
desc[idx[0]].flags = VRING_DESC_F_NEXT;
desc[idx[0]].next = idx[1];
desc[idx[1]].addr = (uint64) b->data;
desc[idx[1]].len = BSIZE;
if(b->flags & B_DIRTY)
desc[idx[1]].flags = 0; // device reads b->data
else
desc[idx[1]].flags = VRING_DESC_F_WRITE; // device writes b->data
desc[idx[1]].flags |= VRING_DESC_F_NEXT;
desc[idx[1]].next = idx[2];
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info[idx[0]].status = 0;
desc[idx[2]].addr = (uint64) &info[idx[0]].status;
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desc[idx[2]].len = 1;
desc[idx[2]].flags = VRING_DESC_F_WRITE; // device writes the status
desc[idx[2]].next = 0;
// record struct buf for virtio_disk_intr().
info[idx[0]].b = b;
// avail[0] is flags
// avail[1] tells the device how far to look in avail[2...].
// avail[2...] are desc[] indices the device should process.
// we only tell device the first index in our chain of descriptors.
avail[2 + (avail[1] % NUM)] = idx[0];
__sync_synchronize();
avail[1] = avail[1] + 1;
*R(VIRTIO_MMIO_QUEUE_NOTIFY) = 0; // value is queue number
// Wait for virtio_disk_intr() to say request has finished.
while((b->flags & (B_VALID|B_DIRTY)) != B_VALID){
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sleep(b, &vdisk_lock);
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}
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release(&vdisk_lock);
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}
void
virtio_disk_intr()
{
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acquire(&vdisk_lock);
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while((used_idx % NUM) != (used->id % NUM)){
int id = used->elems[used_idx].id;
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if(info[id].status != 0)
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panic("virtio_disk_intr status");
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info[id].b->flags |= B_VALID;
info[id].b->flags &= ~B_DIRTY;
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wakeup(info[id].b);
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info[id].b = 0;
free_chain(id);
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used_idx = (used_idx + 1) % NUM;
}
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release(&vdisk_lock);
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}