[PATCH 2.6.18-rc4] aoe [04/14]: zero copy write 1 of 2

Ed L. Cashin
2006-09-20T18:53:07Z

Avoid memory copy on writes.
(This patch depends on fixes in patch 9 to follow.)

Although skb->len should not be set when working with linear skbuffs,
the skb->tail pointer maintained by skb_put/skb_trim is not relevant
to what happens when the skb_fill_page_desc function is called. This
issue was raised without comment in linux-kernel and netdev earlier
this month:

http://thread.gmane.org/gmane.linux.kernel/446474/
http://thread.gmane.org/gmane.linux.network/45444/

So until there is something analogous to skb_put that works for
zero-copy write skbuffs, we will do what the other callers of
skb_fill_page_desc are doing.

Signed-off-by: "Ed L. Cashin" <ecashin@coraid.com>
---

diff -upr 2.6.18-rc4-orig/drivers/block/aoe/aoe.h 2.6.18-rc4-aoe/drivers/block/aoe/aoe.h
--- 2.6.18-rc4-orig/drivers/block/aoe/aoe.h 2006-09-20 14:29:35.000000000 -0400
+++ 2.6.18-rc4-aoe/drivers/block/aoe/aoe.h 2006-09-20 14:29:35.000000000 -0400
@@ -107,11 +107,7 @@ struct frame {
ulong waited;
struct buf *buf;
char *bufaddr;
- int writedatalen;
- int ndata;
-
- /* largest possible */
- unsigned char data[sizeof(struct aoe_hdr) + sizeof(struct aoe_atahdr)];
+ struct sk_buff *skb;
};

struct aoedev {
@@ -157,6 +153,7 @@ void aoecmd_cfg(ushort aoemajor, unsigne
void aoecmd_ata_rsp(struct sk_buff *);
void aoecmd_cfg_rsp(struct sk_buff *);
void aoecmd_sleepwork(void *vp);
+struct sk_buff *new_skb(ulong);

int aoedev_init(void);
void aoedev_exit(void);
diff -upr 2.6.18-rc4-orig/drivers/block/aoe/aoecmd.c 2.6.18-rc4-aoe/drivers/block/aoe/aoecmd.c
--- 2.6.18-rc4-orig/drivers/block/aoe/aoecmd.c 2006-09-20 14:29:35.000000000 -0400
+++ 2.6.18-rc4-aoe/drivers/block/aoe/aoecmd.c 2006-09-20 14:29:35.000000000 -0400
@@ -17,15 +17,14 @@
#define MAXTIMER (HZ << 1)
#define MAXWAIT (60 * 3) /* After MAXWAIT seconds, give up and fail dev */

-static struct sk_buff *
-new_skb(struct net_device *if_dev, ulong len)
+struct sk_buff *
+new_skb(ulong len)
{
struct sk_buff *skb;

skb = alloc_skb(len, GFP_ATOMIC);
if (skb) {
skb->nh.raw = skb->mac.raw = skb->data;
- skb->dev = if_dev;
skb->protocol = __constant_htons(ETH_P_AOE);
skb->priority = 0;
skb_put(skb, len);
@@ -40,29 +39,6 @@ new_skb(struct net_device *if_dev, ulong
return skb;
}

-static struct sk_buff *
-skb_prepare(struct aoedev *d, struct frame *f)
-{
- struct sk_buff *skb;
- char *p;
-
- skb = new_skb(d->ifp, f->ndata + f->writedatalen);
- if (!skb) {
- printk(KERN_INFO "aoe: skb_prepare: failure to allocate skb\n");
- return NULL;
- }
-
- p = skb->mac.raw;
- memcpy(p, f->data, f->ndata);
-
- if (f->writedatalen) {
- p += sizeof(struct aoe_hdr) + sizeof(struct aoe_atahdr);
- memcpy(p, f->bufaddr, f->writedatalen);
- }
-
- return skb;
-}
-
static struct frame *
getframe(struct aoedev *d, int tag)
{
@@ -129,10 +105,11 @@ aoecmd_ata_rw(struct aoedev *d, struct f
bcnt = MAXATADATA;

/* initialize the headers & frame */
- h = (struct aoe_hdr *) f->data;
+ skb = f->skb;
+ h = (struct aoe_hdr *) skb->mac.raw;
ah = (struct aoe_atahdr *) (h+1);
- f->ndata = sizeof *h + sizeof *ah;
- memset(h, 0, f->ndata);
+ skb->len = sizeof *h + sizeof *ah;
+ memset(h, 0, skb->len);
f->tag = aoehdr_atainit(d, h);
f->waited = 0;
f->buf = buf;
@@ -155,11 +132,13 @@ aoecmd_ata_rw(struct aoedev *d, struct f
}

if (bio_data_dir(buf->bio) == WRITE) {
+ skb_fill_page_desc(skb, 0, virt_to_page(f->bufaddr),
+ offset_in_page(f->bufaddr), bcnt);
ah->aflags |= AOEAFL_WRITE;
- f->writedatalen = bcnt;
} else {
+ skb_shinfo(skb)->nr_frags = 0;
+ skb->len = ETH_ZLEN;
writebit = 0;
- f->writedatalen = 0;
}

ah->cmdstat = WIN_READ | writebit | extbit;
@@ -179,15 +158,14 @@ aoecmd_ata_rw(struct aoedev *d, struct f
buf->bufaddr = page_address(buf->bv->bv_page) + buf->bv->bv_offset;
}

- skb = skb_prepare(d, f);
- if (skb) {
- skb->next = NULL;
- if (d->sendq_hd)
- d->sendq_tl->next = skb;
- else
- d->sendq_hd = skb;
- d->sendq_tl = skb;
- }
+ skb->dev = d->ifp;
+ skb_get(skb);
+ skb->next = NULL;
+ if (d->sendq_hd)
+ d->sendq_tl->next = skb;
+ else
+ d->sendq_hd = skb;
+ d->sendq_tl = skb;
}

/* some callers cannot sleep, and they can call this function,
@@ -209,11 +187,12 @@ aoecmd_cfg_pkts(ushort aoemajor, unsigne
if (!is_aoe_netif(ifp))
continue;

- skb = new_skb(ifp, sizeof *h + sizeof *ch);
+ skb = new_skb(sizeof *h + sizeof *ch);
if (skb == NULL) {
printk(KERN_INFO "aoe: aoecmd_cfg: skb alloc failure\n");
continue;
}
+ skb->dev = ifp;
if (sl_tail == NULL)
sl_tail = skb;
h = (struct aoe_hdr *) skb->mac.raw;
@@ -283,21 +262,21 @@ rexmit(struct aoedev *d, struct frame *f
d->aoemajor, d->aoeminor, f->tag, jiffies, n);
aoechr_error(buf);

- h = (struct aoe_hdr *) f->data;
+ skb = f->skb;
+ h = (struct aoe_hdr *) skb->mac.raw;
f->tag = n;
h->tag = cpu_to_be32(n);
memcpy(h->dst, d->addr, sizeof h->dst);
memcpy(h->src, d->ifp->dev_addr, sizeof h->src);

- skb = skb_prepare(d, f);
- if (skb) {
- skb->next = NULL;
- if (d->sendq_hd)
- d->sendq_tl->next = skb;
- else
- d->sendq_hd = skb;
- d->sendq_tl = skb;
- }
+ skb->dev = d->ifp;
+ skb_get(skb);
+ skb->next = NULL;
+ if (d->sendq_hd)
+ d->sendq_tl->next = skb;
+ else
+ d->sendq_hd = skb;
+ d->sendq_tl = skb;
}

static int
@@ -514,7 +493,7 @@ aoecmd_ata_rsp(struct sk_buff *skb)
calc_rttavg(d, tsince(f->tag));

ahin = (struct aoe_atahdr *) (hin+1);
- ahout = (struct aoe_atahdr *) (f->data + sizeof(struct aoe_hdr));
+ ahout = (struct aoe_atahdr *) (f->skb->mac.raw + sizeof(struct aoe_hdr));
buf = f->buf;

if (ahout->cmdstat == WIN_IDENTIFY)
@@ -620,20 +599,21 @@ aoecmd_ata_id(struct aoedev *d)
}

/* initialize the headers & frame */
- h = (struct aoe_hdr *) f->data;
+ skb = f->skb;
+ h = (struct aoe_hdr *) skb->mac.raw;
ah = (struct aoe_atahdr *) (h+1);
- f->ndata = sizeof *h + sizeof *ah;
- memset(h, 0, f->ndata);
+ skb->len = sizeof *h + sizeof *ah;
+ memset(h, 0, skb->len);
f->tag = aoehdr_atainit(d, h);
f->waited = 0;
- f->writedatalen = 0;

/* set up ata header */
ah->scnt = 1;
ah->cmdstat = WIN_IDENTIFY;
ah->lba3 = 0xa0;

- skb = skb_prepare(d, f);
+ skb->dev = d->ifp;
+ skb_get(skb);

d->rttavg = MAXTIMER;
d->timer.function = rexmit_timer;
diff -upr 2.6.18-rc4-orig/drivers/block/aoe/aoedev.c 2.6.18-rc4-aoe/drivers/block/aoe/aoedev.c
--- 2.6.18-rc4-orig/drivers/block/aoe/aoedev.c 2006-09-20 14:29:35.000000000 -0400
+++ 2.6.18-rc4-aoe/drivers/block/aoe/aoedev.c 2006-09-20 14:29:35.000000000 -0400
@@ -63,22 +63,32 @@ aoedev_newdev(ulong nframes)
struct frame *f, *e;

d = kzalloc(sizeof *d, GFP_ATOMIC);
- if (d == NULL)
- return NULL;
f = kcalloc(nframes, sizeof *f, GFP_ATOMIC);
- if (f == NULL) {
- kfree(d);
+ switch (!d || !f) {
+ case 0:
+ d->nframes = nframes;
+ d->frames = f;
+ e = f + nframes;
+ for (; f<e; f++) {
+ f->tag = FREETAG;
+ f->skb = new_skb(ETH_ZLEN);
+ if (!f->skb)
+ break;
+ }
+ if (f == e)
+ break;
+ while (f > d->frames) {
+ f--;
+ dev_kfree_skb(f->skb);
+ }
+ default:
+ if (f)
+ kfree(f);
+ if (d)
+ kfree(d);
return NULL;
}
-
INIT_WORK(&d->work, aoecmd_sleepwork, d);
-
- d->nframes = nframes;
- d->frames = f;
- e = f + nframes;
- for (; f<e; f++)
- f->tag = FREETAG;
-
spin_lock_init(&d->lock);
init_timer(&d->timer);
d->timer.data = (ulong) d;
@@ -160,11 +170,19 @@ aoedev_by_sysminor_m(ulong sysminor, ulo
static void
aoedev_freedev(struct aoedev *d)
{
+ struct frame *f, *e;
+
if (d->gd) {
aoedisk_rm_sysfs(d);
del_gendisk(d->gd);
put_disk(d->gd);
}
+ f = d->frames;
+ e = f + d->nframes;
+ for (; f<e; f++) {
+ skb_shinfo(f->skb)->nr_frags = 0;
+ dev_kfree_skb(f->skb);
+ }
kfree(d->frames);
if (d->bufpool)
mempool_destroy(d->bufpool);