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vhost: don't bother copying iovecs in handle_rx(), kill memcpy_toiovecend()

Browse source 
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2014-12-10 15:51:28 -05:00
commit ba7438aed9
3 changed files with 23 additions and 88 deletions
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82
drivers/vhost/net.c
View file

@ -84,10 +84,6 @@ struct vhost_net_ubuf_ref {
struct vhost_net_virtqueue {
struct vhost_virtqueue vq;
/* hdr is used to store the virtio header.
* Since each iovec has >= 1 byte length, we never need more than
* header length entries to store the header. */
struct iovec hdr[sizeof(struct virtio_net_hdr_mrg_rxbuf)];
size_t vhost_hlen;
size_t sock_hlen;
/* vhost zerocopy support fields below: */
@ -235,44 +231,6 @@ static bool vhost_sock_zcopy(struct socket *sock)
sock_flag(sock->sk, SOCK_ZEROCOPY);
}
/* Pop first len bytes from iovec. Return number of segments used. */
static int move_iovec_hdr(struct iovec *from, struct iovec *to,
size_t len, int iov_count)
{
int seg = 0;
size_t size;
while (len && seg < iov_count) {
size = min(from->iov_len, len);
to->iov_base = from->iov_base;
to->iov_len = size;
from->iov_len -= size;
from->iov_base += size;
len -= size;
++from;
++to;
++seg;
}
return seg;
}
/* Copy iovec entries for len bytes from iovec. */
static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
size_t len, int iovcount)
{
int seg = 0;
size_t size;
while (len && seg < iovcount) {
size = min(from->iov_len, len);
to->iov_base = from->iov_base;
to->iov_len = size;
len -= size;
++from;
++to;
++seg;
}
}
/* In case of DMA done not in order in lower device driver for some reason.
* upend_idx is used to track end of used idx, done_idx is used to track head
* of used idx. Once lower device DMA done contiguously, we will signal KVM
@ -570,9 +528,9 @@ static void handle_rx(struct vhost_net *net)
.msg_controllen = 0,
.msg_flags = MSG_DONTWAIT,
};
struct virtio_net_hdr_mrg_rxbuf hdr = {
.hdr.flags = 0,
.hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
struct virtio_net_hdr hdr = {
.flags = 0,
.gso_type = VIRTIO_NET_HDR_GSO_NONE
};
size_t total_len = 0;
int err, mergeable;
@ -580,6 +538,7 @@ static void handle_rx(struct vhost_net *net)
size_t vhost_hlen, sock_hlen;
size_t vhost_len, sock_len;
struct socket *sock;
struct iov_iter fixup;
mutex_lock(&vq->mutex);
sock = vq->private_data;
@ -624,14 +583,19 @@ static void handle_rx(struct vhost_net *net)
break;
}
/* We don't need to be notified again. */
if (unlikely((vhost_hlen)))
/* Skip header. TODO: support TSO. */
move_iovec_hdr(vq->iov, nvq->hdr, vhost_hlen, in);
else
/* Copy the header for use in VIRTIO_NET_F_MRG_RXBUF:
* needed because recvmsg can modify msg_iov. */
copy_iovec_hdr(vq->iov, nvq->hdr, sock_hlen, in);
iov_iter_init(&msg.msg_iter, READ, vq->iov, in, sock_len);
iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
fixup = msg.msg_iter;
if (unlikely((vhost_hlen))) {
/* We will supply the header ourselves
* TODO: support TSO.
*/
iov_iter_advance(&msg.msg_iter, vhost_hlen);
} else {
/* It'll come from socket; we'll need to patch
* ->num_buffers over if VIRTIO_NET_F_MRG_RXBUF
*/
iov_iter_advance(&fixup, sizeof(hdr));
}
err = sock->ops->recvmsg(NULL, sock, &msg,
sock_len, MSG_DONTWAIT | MSG_TRUNC);
/* Userspace might have consumed the packet meanwhile:
@ -643,18 +607,18 @@ static void handle_rx(struct vhost_net *net)
vhost_discard_vq_desc(vq, headcount);
continue;
}
/* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
if (unlikely(vhost_hlen) &&
memcpy_toiovecend(nvq->hdr, (unsigned char *)&hdr, 0,
vhost_hlen)) {
copy_to_iter(&hdr, sizeof(hdr), &fixup) != sizeof(hdr)) {
vq_err(vq, "Unable to write vnet_hdr at addr %p\n",
vq->iov->iov_base);
break;
}
/* TODO: Should check and handle checksum. */
/* Supply (or replace) ->num_buffers if VIRTIO_NET_F_MRG_RXBUF
* TODO: Should check and handle checksum.
*/
if (likely(mergeable) &&
memcpy_toiovecend(nvq->hdr, (unsigned char *)&headcount,
offsetof(typeof(hdr), num_buffers),
sizeof hdr.num_buffers)) {
copy_to_iter(&headcount, 2, &fixup) != 2) {
vq_err(vq, "Failed num_buffers write");
vhost_discard_vq_desc(vq, headcount);
break;

3
include/linux/uio.h
View file

@ -137,7 +137,4 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, struct io
int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
int offset, int len);
int memcpy_toiovecend(const struct iovec *v, unsigned char *kdata,
int offset, int len);
#endif

26
lib/iovec.c
View file

@ -2,32 +2,6 @@
#include <linux/export.h>
#include <linux/uio.h>
/*
* Copy kernel to iovec. Returns -EFAULT on error.
*/
int memcpy_toiovecend(const struct iovec *iov, unsigned char *kdata,
int offset, int len)
{
int copy;
for (; len > 0; ++iov) {
/* Skip over the finished iovecs */
if (unlikely(offset >= iov->iov_len)) {
offset -= iov->iov_len;
continue;
}
copy = min_t(unsigned int, iov->iov_len - offset, len);
if (copy_to_user(iov->iov_base + offset, kdata, copy))
return -EFAULT;
offset = 0;
kdata += copy;
len -= copy;
}
return 0;
}
EXPORT_SYMBOL(memcpy_toiovecend);
/*
* Copy iovec to kernel. Returns -EFAULT on error.
*/