aoe: zero copy write 1 of 2

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>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 30 insertions, 12 deletions

diff --git a/drivers/block/aoe/aoedev.c b/drivers/block/aoe/aoedev.c
index c7e05ed82512..abf1d3c073e3 100644
--- a/drivers/block/aoe/aoedev.c
+++ b/drivers/block/aoe/aoedev.c
@@ -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, ulong bufcnt)
 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);