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Message-Id: <200712191831.07804.rusty@rustcorp.com.au>
Date: Wed, 19 Dec 2007 18:31:06 +1100
From: Rusty Russell <rusty@...tcorp.com.au>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
linux-ide@...r.kernel.org
Subject: [PATCH 2/7] sg_ring: use in virtio.
Using sg_rings, we can join together scatterlists returned by other
subsystems, without needing to allocate an extra element for chaining.
This helps the virtio_blk device which wants to prepend and append
metadata to the request's scatterlist.
As an added bonus, the old virtio layer used to pass a scatterlist
array and two numbers indicating the number of readable and writable
elements respectively; now we can simply hand two sg_rings which is
much clearer (each sg_ring contains its own length).
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
drivers/block/virtio_blk.c | 33 ++++++++-------
drivers/char/virtio_console.c | 13 +++---
drivers/net/virtio_net.c | 22 +++++-----
drivers/virtio/virtio_ring.c | 90 ++++++++++++++++++++++++++--------------
include/linux/virtio.h | 12 ++---
5 files changed, 99 insertions(+), 71 deletions(-)
diff -r 6fe7cf582293 drivers/block/virtio_blk.c
--- a/drivers/block/virtio_blk.c Wed Dec 19 16:06:43 2007 +1100
+++ b/drivers/block/virtio_blk.c Wed Dec 19 18:29:58 2007 +1100
@@ -5,8 +5,6 @@
#include <linux/virtio.h>
#include <linux/virtio_blk.h>
#include <linux/scatterlist.h>
-
-#define VIRTIO_MAX_SG (3+MAX_PHYS_SEGMENTS)
static unsigned char virtblk_index = 'a';
struct virtio_blk
@@ -24,8 +22,10 @@ struct virtio_blk
mempool_t *pool;
- /* Scatterlist: can be too big for stack. */
- struct scatterlist sg[VIRTIO_MAX_SG];
+ /* Scatterlist ring: can be too big for stack. */
+ DECLARE_SG_RING(out, 1);
+ DECLARE_SG_RING(in, 1);
+ DECLARE_SG_RING(sg, MAX_PHYS_SEGMENTS);
};
struct virtblk_req
@@ -70,8 +70,8 @@ static bool do_req(struct request_queue
static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
struct request *req)
{
- unsigned long num, out, in;
struct virtblk_req *vbr;
+ struct sg_ring *in;
vbr = mempool_alloc(vblk->pool, GFP_ATOMIC);
if (!vbr)
@@ -95,23 +95,24 @@ static bool do_req(struct request_queue
if (blk_barrier_rq(vbr->req))
vbr->out_hdr.type |= VIRTIO_BLK_T_BARRIER;
- /* This init could be done at vblk creation time */
- sg_init_table(vblk->sg, VIRTIO_MAX_SG);
- sg_set_buf(&vblk->sg[0], &vbr->out_hdr, sizeof(vbr->out_hdr));
- num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
- sg_set_buf(&vblk->sg[num+1], &vbr->in_hdr, sizeof(vbr->in_hdr));
+ sg_ring_single(&vblk->out.ring, &vbr->out_hdr, sizeof(vbr->out_hdr));
+ sg_ring_init(&vblk->sg.ring, ARRAY_SIZE(vblk->sg.sg));
+ vblk->sg.ring.num = blk_rq_map_sg(q, vbr->req, vblk->sg.sg);
+ sg_ring_single(&vblk->in.ring, &vbr->in_hdr, sizeof(vbr->in_hdr));
if (rq_data_dir(vbr->req) == WRITE) {
vbr->out_hdr.type |= VIRTIO_BLK_T_OUT;
- out = 1 + num;
- in = 1;
+ /* Chain write request onto output buffers. */
+ list_add_tail(&vblk->sg.ring.list, &vblk->out.ring.list);
+ in = &vblk->in.ring;
} else {
vbr->out_hdr.type |= VIRTIO_BLK_T_IN;
- out = 1;
- in = 1 + num;
+ /* Chain input (status) buffer at end of read buffers. */
+ list_add_tail(&vblk->in.ring.list, &vblk->sg.ring.list);
+ in = &vblk->sg.ring;
}
- if (vblk->vq->vq_ops->add_buf(vblk->vq, vblk->sg, out, in, vbr)) {
+ if (vblk->vq->vq_ops->add_buf(vblk->vq, &vblk->out.ring, in, vbr)) {
mempool_free(vbr, vblk->pool);
return false;
}
@@ -128,7 +129,7 @@ static void do_virtblk_request(struct re
while ((req = elv_next_request(q)) != NULL) {
vblk = req->rq_disk->private_data;
- BUG_ON(req->nr_phys_segments > ARRAY_SIZE(vblk->sg));
+ BUG_ON(req->nr_phys_segments > ARRAY_SIZE(vblk->sg.sg));
/* If this request fails, stop queue and wait for something to
finish to restart it. */
diff -r 6fe7cf582293 drivers/char/virtio_console.c
--- a/drivers/char/virtio_console.c Wed Dec 19 16:06:43 2007 +1100
+++ b/drivers/char/virtio_console.c Wed Dec 19 18:29:58 2007 +1100
@@ -54,15 +54,15 @@ static struct hv_ops virtio_cons;
* immediately (lguest's Launcher does). */
static int put_chars(u32 vtermno, const char *buf, int count)
{
- struct scatterlist sg[1];
+ DECLARE_SG_RING(sg, 1);
unsigned int len;
/* This is a convenient routine to initialize a single-elem sg list */
- sg_init_one(sg, buf, count);
+ sg_ring_single(&sg.ring, buf, count);
/* add_buf wants a token to identify this buffer: we hand it any
* non-NULL pointer, since there's only ever one buffer. */
- if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
+ if (out_vq->vq_ops->add_buf(out_vq, &sg.ring, NULL, (void *)1) == 0) {
/* Tell Host to go! */
out_vq->vq_ops->kick(out_vq);
/* Chill out until it's done with the buffer. */
@@ -78,11 +78,12 @@ static int put_chars(u32 vtermno, const
* queue. */
static void add_inbuf(void)
{
- struct scatterlist sg[1];
- sg_init_one(sg, inbuf, PAGE_SIZE);
+ DECLARE_SG_RING(sg, 1);
+
+ sg_ring_single(&sg.ring, inbuf, PAGE_SIZE);
/* We should always be able to add one buffer to an empty queue. */
- if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0)
+ if (in_vq->vq_ops->add_buf(in_vq, NULL, &sg.ring, inbuf) != 0)
BUG();
in_vq->vq_ops->kick(in_vq);
}
diff -r 6fe7cf582293 drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c Wed Dec 19 16:06:43 2007 +1100
+++ b/drivers/net/virtio_net.c Wed Dec 19 18:29:58 2007 +1100
@@ -211,21 +211,21 @@ static void try_fill_recv(struct virtnet
static void try_fill_recv(struct virtnet_info *vi)
{
struct sk_buff *skb;
- struct scatterlist sg[1+MAX_SKB_FRAGS];
- int num, err;
+ DECLARE_SG_RING(sg, 1+MAX_SKB_FRAGS);
+ int err;
- sg_init_table(sg, 1+MAX_SKB_FRAGS);
+ sg_ring_init(&sg.ring, 1+MAX_SKB_FRAGS);
for (;;) {
skb = netdev_alloc_skb(vi->dev, MAX_PACKET_LEN);
if (unlikely(!skb))
break;
skb_put(skb, MAX_PACKET_LEN);
- vnet_hdr_to_sg(sg, skb);
- num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
+ vnet_hdr_to_sg(sg.sg, skb);
+ sg.ring.num = skb_to_sgvec(skb, sg.sg+1, 0, skb->len) + 1;
skb_queue_head(&vi->recv, skb);
- err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
+ err = vi->rvq->vq_ops->add_buf(vi->rvq, NULL, &sg.ring, skb);
if (err) {
skb_unlink(skb, &vi->recv);
kfree_skb(skb);
@@ -304,13 +304,13 @@ static int start_xmit(struct sk_buff *sk
static int start_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct virtnet_info *vi = netdev_priv(dev);
- int num, err;
- struct scatterlist sg[1+MAX_SKB_FRAGS];
+ int err;
+ DECLARE_SG_RING(sg, 1+MAX_SKB_FRAGS);
struct virtio_net_hdr *hdr;
const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
DECLARE_MAC_BUF(mac);
- sg_init_table(sg, 1+MAX_SKB_FRAGS);
+ sg_ring_init(&sg.ring, 1+MAX_SKB_FRAGS);
pr_debug("%s: xmit %p %s\n", dev->name, skb, print_mac(mac, dest));
@@ -345,13 +345,13 @@ static int start_xmit(struct sk_buff *sk
hdr->gso_size = 0;
}
- vnet_hdr_to_sg(sg, skb);
- num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
+ vnet_hdr_to_sg(sg.sg, skb);
+ sg.ring.num = skb_to_sgvec(skb, sg.sg+1, 0, skb->len) + 1;
__skb_queue_head(&vi->send, skb);
- vi->stats.sendq_sglen += num;
+ vi->stats.sendq_sglen += sg.ring.num;
again:
- err = vi->svq->vq_ops->add_buf(vi->svq, sg, num, 0, skb);
+ err = vi->svq->vq_ops->add_buf(vi->svq, &sg.ring, NULL, skb);
if (err) {
vi->stats.sendq_full++;
diff -r 6fe7cf582293 drivers/virtio/virtio_ring.c
--- a/drivers/virtio/virtio_ring.c Wed Dec 19 16:06:43 2007 +1100
+++ b/drivers/virtio/virtio_ring.c Wed Dec 19 18:29:58 2007 +1100
@@ -69,48 +69,62 @@ struct vring_virtqueue
#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
+static int add_desc(struct vring_virtqueue *vq, unsigned int i,
+ struct scatterlist *sg, unsigned int flags)
+{
+ if (vq->num_free == 0)
+ return -ENOSPC;
+
+ vq->vring.desc[i].flags = VRING_DESC_F_NEXT | flags;
+ vq->vring.desc[i].addr = (page_to_pfn(sg_page(sg))<<PAGE_SHIFT)
+ + sg->offset;
+ vq->vring.desc[i].len = sg->length;
+ vq->num_free--;
+ return vq->vring.desc[i].next;
+}
+
static int vring_add_buf(struct virtqueue *_vq,
- struct scatterlist sg[],
- unsigned int out,
- unsigned int in,
+ struct sg_ring *out,
+ struct sg_ring *in,
void *data)
{
struct vring_virtqueue *vq = to_vvq(_vq);
- unsigned int i, avail, head, uninitialized_var(prev);
+ unsigned int j, avail, head, free, uninitialized_var(prev);
+ int i;
+ struct sg_ring empty_sg, *sg;
BUG_ON(data == NULL);
- BUG_ON(out + in > vq->vring.num);
- BUG_ON(out + in == 0);
+
+ sg_ring_init(&empty_sg, 0);
+ empty_sg.num = 0;
+ if (!out)
+ out = &empty_sg;
+ if (!in)
+ in = &empty_sg;
+
+ BUG_ON(in->num == 0 && out->num == 0);
START_USE(vq);
- if (vq->num_free < out + in) {
- pr_debug("Can't add buf len %i - avail = %i\n",
- out + in, vq->num_free);
- END_USE(vq);
- return -ENOSPC;
+ i = head = vq->free_head;
+ free = vq->num_free;
+
+ /* Lay out the output buffers first. */
+ sg_ring_for_each(out, sg, j) {
+ prev = i;
+ i = add_desc(vq, i, &sg->sg[j], 0);
+ if (unlikely(i < 0))
+ goto full;
}
- /* We're about to use some buffers from the free list. */
- vq->num_free -= out + in;
+ /* Lay out the input buffers next. */
+ sg_ring_for_each(in, sg, j) {
+ prev = i;
+ i = add_desc(vq, i, &sg->sg[j], VRING_DESC_F_WRITE);
+ if (unlikely(i < 0))
+ goto full;
+ }
- head = vq->free_head;
- for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
- vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
- vq->vring.desc[i].addr = (page_to_pfn(sg_page(sg))<<PAGE_SHIFT)
- + sg->offset;
- vq->vring.desc[i].len = sg->length;
- prev = i;
- sg++;
- }
- for (; in; i = vq->vring.desc[i].next, in--) {
- vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
- vq->vring.desc[i].addr = (page_to_pfn(sg_page(sg))<<PAGE_SHIFT)
- + sg->offset;
- vq->vring.desc[i].len = sg->length;
- prev = i;
- sg++;
- }
/* Last one doesn't continue. */
vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
@@ -128,6 +142,12 @@ static int vring_add_buf(struct virtqueu
pr_debug("Added buffer head %i to %p\n", head, vq);
END_USE(vq);
return 0;
+
+full:
+ pr_debug("Buffer needed more than %u on %p\n", free, vq);
+ vq->num_free = free;
+ END_USE(vq);
+ return i;
}
static void vring_kick(struct virtqueue *_vq)
diff -r 6fe7cf582293 include/linux/virtio.h
--- a/include/linux/virtio.h Wed Dec 19 16:06:43 2007 +1100
+++ b/include/linux/virtio.h Wed Dec 19 18:29:58 2007 +1100
@@ -3,7 +3,7 @@
/* Everything a virtio driver needs to work with any particular virtio
* implementation. */
#include <linux/types.h>
-#include <linux/scatterlist.h>
+#include <linux/sg_ring.h>
#include <linux/spinlock.h>
#include <linux/device.h>
#include <linux/mod_devicetable.h>
@@ -27,9 +27,8 @@ struct virtqueue
* virtqueue_ops - operations for virtqueue abstraction layer
* @add_buf: expose buffer to other end
* vq: the struct virtqueue we're talking about.
- * sg: the description of the buffer(s).
- * out_num: the number of sg readable by other side
- * in_num: the number of sg which are writable (after readable ones)
+ * out: the scatter gather elements readable by other side (can be NULL)
+ * in: the scatter gather elements which are writable (can be NULL)
* data: the token identifying the buffer.
* Returns 0 or an error.
* @kick: update after add_buf
@@ -56,9 +55,8 @@ struct virtqueue
*/
struct virtqueue_ops {
int (*add_buf)(struct virtqueue *vq,
- struct scatterlist sg[],
- unsigned int out_num,
- unsigned int in_num,
+ struct sg_ring *out,
+ struct sg_ring *in,
void *data);
void (*kick)(struct virtqueue *vq);
diff -r 6fe7cf582293 net/9p/trans_virtio.c
--- a/net/9p/trans_virtio.c Wed Dec 19 16:06:43 2007 +1100
+++ b/net/9p/trans_virtio.c Wed Dec 19 18:29:59 2007 +1100
@@ -88,7 +88,7 @@ static int p9_virtio_write(struct p9_tra
{
struct virtio_chan *chan = (struct virtio_chan *) trans->priv;
struct virtqueue *out_vq = chan->out_vq;
- struct scatterlist sg[1];
+ DECLARE_SG_RING(sg, 1);
unsigned int len;
P9_DPRINTK(P9_DEBUG_TRANS, "9p debug: virtio write (%d)\n", count);
@@ -97,11 +97,11 @@ static int p9_virtio_write(struct p9_tra
if (rest_of_page(buf) < count)
count = rest_of_page(buf);
- sg_init_one(sg, buf, count);
+ sg_ring_single(&sg.ring, buf, count);
/* add_buf wants a token to identify this buffer: we hand it any
* non-NULL pointer, since there's only ever one buffer. */
- if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
+ if (out_vq->vq_ops->add_buf(out_vq, &sg.ring, NULL, (void *)1) == 0) {
/* Tell Host to go! */
out_vq->vq_ops->kick(out_vq);
/* Chill out until it's done with the buffer. */
@@ -119,12 +119,12 @@ static int p9_virtio_write(struct p9_tra
* queue. */
static void add_inbuf(struct virtio_chan *chan)
{
- struct scatterlist sg[1];
+ DECLARE_SG_RING(sg, 1);
- sg_init_one(sg, chan->inbuf, PAGE_SIZE);
+ sg_ring_single(&sg.ring, chan->inbuf, PAGE_SIZE);
/* We should always be able to add one buffer to an empty queue. */
- if (chan->in_vq->vq_ops->add_buf(chan->in_vq, sg, 0, 1, chan->inbuf))
+ if (chan->in_vq->vq_ops->add_buf(chan->in_vq,&sg.ring,NULL,chan->inbuf))
BUG();
chan->in_vq->vq_ops->kick(chan->in_vq);
}
--
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