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Date:	Fri, 18 Apr 2008 17:16:24 +0530
From:	"pradeep singh rautela" <rautelap@...il.com>
To:	"Rusty Russell" <rusty@...tcorp.com.au>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Max Krasnyansky" <maxk@...lcomm.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 5/5] tun: vringfd xmit support.

On Fri, Apr 18, 2008 at 10:13 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> This patch modifies tun to allow a vringfd to specify the send
>  buffer.  The user does a write to push out packets from the buffer.
>
>  Again we use the 'struct virtio_net_hdr' to allow userspace to send
>  GSO packets.  In this case, it can hint how much to copy, and the
>  other pages will be made into skb fragments.
>
>  Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>  ---
>   drivers/net/tun.c      |  410 +++++++++++++++++++++++++++++++++++++++++--------
>   include/linux/if_tun.h |    1
>   2 files changed, 351 insertions(+), 60 deletions(-)
>
>  diff -r f797ec115d1b drivers/net/tun.c
>  --- a/drivers/net/tun.c Fri Apr 18 05:58:40 2008 +1000
>  +++ b/drivers/net/tun.c Fri Apr 18 06:07:21 2008 +1000
>  @@ -65,6 +65,8 @@
>   #include <linux/vring.h>
>   #include <linux/virtio_net.h>
>   #include <linux/file.h>
>  +#include <linux/spinlock.h>
>  +#include <linux/kthread.h>
>   #include <net/net_namespace.h>
>
>   #include <asm/system.h>
>  @@ -102,8 +104,8 @@ struct tun_struct {
>         u32 chr_filter[2];
>         u32 net_filter[2];
>
>  -       struct vring_info       *inring;
>  -       struct file             *infile;
>  +       struct vring_info       *inring, *outring;
>  +       struct file             *infile, *outfile;
>
>   #ifdef TUN_DEBUG
>         int debug;
>  @@ -258,6 +261,169 @@ static void tun_net_init(struct net_devi
>                 dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
>                 break;
>         }
>  +}
>  +
>  +/* We don't consolidate consecutive iovecs, so huge iovecs can break here.
>  + * Users will learn not to do that. */
>  +static int get_user_skb_frags(const struct iovec *iv, size_t len,
>  +                             struct skb_frag_struct *f)
>  +{
>  +       unsigned int i, j, num_pg = 0;
>  +       int err;
>  +       struct page *pages[MAX_SKB_FRAGS];
>  +
>  +       down_read(&current->mm->mmap_sem);
>  +       while (len) {
>  +               int n, npages;
>  +               unsigned long base, len;
>  +               base = (unsigned long)iv->iov_base;
>  +               len = (unsigned long)iv->iov_len;
>  +
>  +               if (len == 0) {
>  +                       iv++;
>  +                       continue;
>  +               }
>  +
>  +               /* How many pages will this take? */
>  +               npages = 1 + (base + len - 1)/PAGE_SIZE - base/PAGE_SIZE;

Hi Rusty,
A trivial suggestion, how about
          npages = 1+(len -1)/PAGE_SIZE ?

Thanks,
         --Pradeep
>  +               if (unlikely(num_pg + npages > MAX_SKB_FRAGS)) {
>  +                       err = -ENOSPC;
>  +                       goto fail;
>  +               }
>  +               n = get_user_pages(current, current->mm, base, npages,
>  +                                  0, 0, pages, NULL);
>  +               if (unlikely(n < 0)) {
>  +                       err = n;
>  +                       goto fail;
>  +               }
>  +
>  +               /* Transfer pages to the frag array */
>  +               for (j = 0; j < n; j++) {
>  +                       f[num_pg].page = pages[j];
>  +                       if (j == 0) {
>  +                               f[num_pg].page_offset = offset_in_page(base);
>  +                               f[num_pg].size = min(len, PAGE_SIZE -
>  +                                                    f[num_pg].page_offset);
>  +                       } else {
>  +                               f[num_pg].page_offset = 0;
>  +                               f[num_pg].size = min(len, PAGE_SIZE);
>  +                       }
>  +                       len -= f[num_pg].size;
>  +                       base += f[num_pg].size;
>  +                       num_pg++;
>  +               }
>  +
>  +               if (unlikely(n != npages)) {
>  +                       err = -EFAULT;
>  +                       goto fail;
>  +               }
>  +       }
>  +       up_read(&current->mm->mmap_sem);
>  +       return num_pg;
>  +
>  +fail:
>  +       for (i = 0; i < num_pg; i++)
>  +               put_page(f[i].page);
>  +       up_read(&current->mm->mmap_sem);
>  +       return err;
>  +}
>  +
>  +/* We actually store this at the head of the skb. */
>  +struct skb_tun_hdr {
>  +       struct list_head list;
>  +       struct tun_struct *tun;
>  +       unsigned int id;
>  +       unsigned int len;
>  +};
>  +
>  +/* Get packet from user space buffer.  copylen is a hint as to how
>  + * much to copy (rest is pinned).  */
>  +static struct sk_buff *get_user_skb(struct tun_struct *tun, struct iovec *iv,
>  +                                   size_t copylen, size_t len)
>  +{
>  +       struct tun_pi pi = { 0, __constant_htons(ETH_P_IP) };
>  +       struct sk_buff *skb;
>  +       size_t align = 0, extra = 0;
>  +       int err;
>  +
>  +       if (!(tun->flags & TUN_NO_PI)) {
>  +               if (len < sizeof(pi)) {
>  +                       err = -EINVAL;
>  +                       goto fail;
>  +               }
>  +               len -= sizeof(pi);
>  +
>  +               if (memcpy_fromiovec((void *)&pi, iv, sizeof(pi))) {
>  +                       err = -EFAULT;
>  +                       goto fail;
>  +               }
>  +               if (copylen > len)
>  +                       copylen = len;
>  +       }
>  +
>  +       if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
>  +               align = NET_IP_ALIGN;
>  +               if (unlikely(copylen < ETH_HLEN)) {
>  +                       if (len < ETH_HLEN) {
>  +                               err = -EINVAL;
>  +                               goto fail;
>  +                       }
>  +                       copylen = ETH_HLEN;
>  +               }
>  +       }
>  +
>  +       /* Allocate extra header if we need  */
>  +       if (copylen != len)
>  +               extra = sizeof(struct skb_tun_hdr);
>  +
>  +       skb = alloc_skb(extra + copylen + align, GFP_KERNEL);
>  +       if (!skb) {
>  +               err = -ENOMEM;
>  +               goto fail;
>  +       }
>  +
>  +       if (extra + align)
>  +               skb_reserve(skb, extra + align);
>  +
>  +       if (memcpy_fromiovec(skb_put(skb, copylen), iv, copylen)) {
>  +               err = -EFAULT;
>  +               goto free_skb;
>  +       }
>  +
>  +       switch (tun->flags & TUN_TYPE_MASK) {
>  +       case TUN_TUN_DEV:
>  +               skb_reset_mac_header(skb);
>  +               skb->protocol = pi.proto;
>  +               skb->dev = tun->dev;
>  +               break;
>  +       case TUN_TAP_DEV:
>  +               skb->protocol = eth_type_trans(skb, tun->dev);
>  +               break;
>  +       };
>  +
>  +       if (tun->flags & TUN_NOCHECKSUM)
>  +               skb->ip_summed = CHECKSUM_UNNECESSARY;
>  +
>  +       /* Anything left gets put into frags. */
>  +       if (extra) {
>  +               struct skb_shared_info *sinfo = skb_shinfo(skb);
>  +               int err = get_user_skb_frags(iv, len - copylen, sinfo->frags);
>  +               if (err < 0)
>  +                       goto free_skb;
>  +               sinfo->nr_frags = err;
>  +       }
>  +       tun->dev->last_rx = jiffies;
>  +
>  +       tun->dev->stats.rx_packets++;
>  +       tun->dev->stats.rx_bytes += len;
>  +
>  +       return skb;
>  +
>  +free_skb:
>  +       kfree_skb(skb);
>  +fail:
>  +       tun->dev->stats.rx_dropped++;
>  +       return ERR_PTR(err);
>   }
>
>   #if defined(CONFIG_VRING) || defined(CONFIG_VRING_MODULE)
>  @@ -355,6 +521,132 @@ static struct vring_ops recvops = {
>         .pull = pull_recv_skbs,
>   };
>
>  +static DEFINE_SPINLOCK(finished_lock);
>  +static LIST_HEAD(shinfo_finished_list);
>  +static struct task_struct *shinfo_finisher;
>  +
>  +static void used_buffer(struct skb_tun_hdr *tunh)
>  +{
>  +       /* Woot, something happened. */
>  +       vring_wake(tunh->tun->outring);
>  +
>  +       /* Release device.  Keeping this reference blocks file close. */
>  +       dev_put(tunh->tun->dev);
>  +
>  +       /* tunh == skb->head. */
>  +       kfree(tunh);
>  +}
>  +
>  +static int do_shinfo_finisher(void *unused)
>  +{
>  +       LIST_HEAD(list);
>  +       struct skb_tun_hdr *i;
>  +
>  +       while (!kthread_should_stop()) {
>  +               set_current_state(TASK_INTERRUPTIBLE);
>  +
>  +               spin_lock_irq(&finished_lock);
>  +               list_splice_init(&list, &shinfo_finished_list);
>  +               spin_unlock_irq(&finished_lock);
>  +
>  +               if (list_empty(&list)) {
>  +                       schedule();
>  +                       continue;
>  +               }
>  +
>  +               list_for_each_entry(i, &list, list) {
>  +                       vring_used_buffer(i->tun->outring, i->id, i->len);
>  +                       used_buffer(i);
>  +               }
>  +       }
>  +       return 0;
>  +}
>  +
>  +/* We are done with this skb data: put it in the used pile. */
>  +static void shinfo_finished(struct skb_shared_info *sinfo)
>  +{
>  +       struct skb_tun_hdr *tunh = (void *)skb_shinfo_to_head(sinfo);
>  +       unsigned long flags;
>  +
>  +       spin_lock_irqsave(&finished_lock, flags);
>  +       list_add(&tunh->list, &shinfo_finished_list);
>  +       spin_unlock_irqrestore(&finished_lock, flags);
>  +
>  +       wake_up_process(shinfo_finisher);
>  +}
>  +
>  +static int xmit_packets(void *_tun)
>  +{
>  +       struct tun_struct *tun = _tun;
>  +       struct iovec iov[1+MAX_SKB_FRAGS];
>  +       unsigned int iovnum = ARRAY_SIZE(iov);
>  +       int id, err, wake = 0;
>  +       unsigned long len;
>  +
>  +       while ((id = vring_get_buffer(tun->outring, NULL, NULL, NULL,
>  +                                     iov, &iovnum, &len)) > 0) {
>  +               struct virtio_net_hdr h;
>  +               struct sk_buff *skb;
>  +               struct skb_shared_info *shinfo;
>  +
>  +               if (unlikely(len < sizeof(h)))
>  +                       return -EINVAL;
>  +
>  +               err = memcpy_fromiovec((void *)&h, iov, sizeof(h));
>  +               if (unlikely(err))
>  +                       return -EFAULT;
>  +
>  +               len -= sizeof(h);
>  +               if (h.hdr_len > len)
>  +                       return -EINVAL;
>  +
>  +               /* Without GSO, we copy entire packet. */
>  +               if (h.gso_type == VIRTIO_NET_HDR_GSO_NONE)
>  +                       h.hdr_len = len;
>  +
>  +               skb = get_user_skb(tun, iov, h.hdr_len, len);
>  +               if (IS_ERR(skb))
>  +                       return PTR_ERR(skb);
>  +
>  +               if ((h.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
>  +                   !skb_partial_csum_set(skb, h.csum_start, h.csum_offset)) {
>  +                       kfree_skb(skb);
>  +                       return -EINVAL;
>  +               }
>  +
>  +               /* If it has fragments, set up destructor for later. */
>  +               shinfo = skb_shinfo(skb);
>  +               if (skb_shinfo(skb)->nr_frags) {
>  +                       struct skb_tun_hdr *tunh = (void *)skb->head;
>  +                       shinfo->destructor = shinfo_finished;
>  +                       tunh->id = id;
>  +                       tunh->len = sizeof(h) + skb->len;
>  +               } else {
>  +                       vring_used_buffer(tun->outring, id, sizeof(h)+skb->len);
>  +                       wake = 1;
>  +               }
>  +               netif_rx_ni(skb);
>  +       }
>  +
>  +       if (wake)
>  +               vring_wake(tun->outring);
>  +
>  +       /* 0 or error. */
>  +       return id;
>  +}
>  +
>  +static struct vring_ops xmitops = {
>  +       .push = xmit_packets,
>  +};
>  +
>  +static int init_vring(void)
>  +{
>  +       shinfo_finisher = kthread_run(do_shinfo_finisher, NULL, "tun");
>  +       if (IS_ERR(shinfo_finisher))
>  +               return PTR_ERR(shinfo_finisher);
>  +       return 0;
>  +}
>  +
>   static int set_recv_vring(struct tun_struct *tun, int fd)
>   {
>         int err;
>  @@ -391,9 +685,47 @@ static void unset_vrings(struct tun_stru
>                 vring_unset_ops(tun->inring);
>                 fput(tun->infile);
>         }
>  +       if (tun->outring) {
>  +               vring_unset_ops(tun->outring);
>  +               fput(tun->outfile);
>  +       }
>  +}
>  +
>  +static int set_xmit_vring(struct tun_struct *tun, int fd)
>  +{
>  +       int err;
>  +
>  +       if (tun->outring)
>  +               return -EBUSY;
>  +
>  +       tun->outfile = fget(fd);
>  +       if (!tun->outfile)
>  +               return -EBADF;
>  +
>  +       tun->outring = vring_get(tun->outfile);
>  +       if (!tun->outring) {
>  +               err = -EBADF;
>  +               goto put;
>  +       }
>  +
>  +       err = vring_set_ops(tun->outring, &xmitops, tun);
>  +       if (err) {
>  +               tun->outring = NULL;
>  +               goto put;
>  +       }
>  +       return 0;
>  +
>  +put:
>  +       fput(tun->outfile);
>  +       tun->outfile = NULL;
>  +       return err;
>   }
>   #else /* ... !CONFIG_VRING */
>   static int set_recv_vring(struct tun_struct *tun, int fd)
>  +{
>  +       return -ENOTTY;
>  +}
>  +static int set_xmit_vring(struct tun_struct *tun, int fd)
>   {
>         return -ENOTTY;
>   }
>  @@ -424,74 +756,26 @@ static unsigned int tun_chr_poll(struct
>         return mask;
>   }
>
>  -/* Get packet from user space buffer */
>  -static __inline__ ssize_t tun_get_user(struct tun_struct *tun, struct iovec *iv, size_t count)
>  -{
>  -       struct tun_pi pi = { 0, __constant_htons(ETH_P_IP) };
>  -       struct sk_buff *skb;
>  -       size_t len = count, align = 0;
>  -
>  -       if (!(tun->flags & TUN_NO_PI)) {
>  -               if ((len -= sizeof(pi)) > count)
>  -                       return -EINVAL;
>  -
>  -               if(memcpy_fromiovec((void *)&pi, iv, sizeof(pi)))
>  -                       return -EFAULT;
>  -       }
>  -
>  -       if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
>  -               align = NET_IP_ALIGN;
>  -               if (unlikely(len < ETH_HLEN))
>  -                       return -EINVAL;
>  -       }
>  -
>  -       if (!(skb = alloc_skb(len + align, GFP_KERNEL))) {
>  -               tun->dev->stats.rx_dropped++;
>  -               return -ENOMEM;
>  -       }
>  -
>  -       if (align)
>  -               skb_reserve(skb, align);
>  -       if (memcpy_fromiovec(skb_put(skb, len), iv, len)) {
>  -               tun->dev->stats.rx_dropped++;
>  -               kfree_skb(skb);
>  -               return -EFAULT;
>  -       }
>  -
>  -       switch (tun->flags & TUN_TYPE_MASK) {
>  -       case TUN_TUN_DEV:
>  -               skb_reset_mac_header(skb);
>  -               skb->protocol = pi.proto;
>  -               skb->dev = tun->dev;
>  -               break;
>  -       case TUN_TAP_DEV:
>  -               skb->protocol = eth_type_trans(skb, tun->dev);
>  -               break;
>  -       };
>  -
>  -       if (tun->flags & TUN_NOCHECKSUM)
>  -               skb->ip_summed = CHECKSUM_UNNECESSARY;
>  -
>  -       netif_rx_ni(skb);
>  -       tun->dev->last_rx = jiffies;
>  -
>  -       tun->dev->stats.rx_packets++;
>  -       tun->dev->stats.rx_bytes += len;
>  -
>  -       return count;
>  -}
>  -
>   static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
>                               unsigned long count, loff_t pos)
>   {
>         struct tun_struct *tun = iocb->ki_filp->private_data;
>  +       size_t len;
>  +       struct sk_buff *skb;
>
>         if (!tun)
>                 return -EBADFD;
>
>         DBG(KERN_INFO "%s: tun_chr_write %ld\n", tun->dev->name, count);
>
>  -       return tun_get_user(tun, (struct iovec *) iv, iov_length(iv, count));
>  +       len = iov_length(iv, count);
>  +
>  +       skb = get_user_skb(tun, (struct iovec *)iv, len, len);
>  +       if (IS_ERR(skb))
>  +               return PTR_ERR(skb);
>  +
>  +       netif_rx_ni(skb);
>  +       return len;
>   }
>
>   /* Put packet to the user space buffer */
>  @@ -831,6 +1115,9 @@ static int tun_chr_ioctl(struct inode *i
>         case TUNSETRECVVRING:
>                 return set_recv_vring(tun, arg);
>
>  +       case TUNSETXMITVRING:
>  +               return set_xmit_vring(tun, arg);
>  +
>         case SIOCGIFFLAGS:
>                 ifr.ifr_flags = tun->if_flags;
>                 if (copy_to_user( argp, &ifr, sizeof ifr))
>  @@ -1078,6 +1365,12 @@ static int __init tun_init(void)
>         ret = misc_register(&tun_miscdev);
>         if (ret)
>                 printk(KERN_ERR "tun: Can't register misc device %d\n", TUN_MINOR);
>  +       else {
>  +               ret = init_vring();
>  +               if (ret)
>  +                       misc_deregister(&tun_miscdev);
>  +       }
>  +
>         return ret;
>   }
>
>  diff -r f797ec115d1b include/linux/if_tun.h
>  --- a/include/linux/if_tun.h    Fri Apr 18 05:58:40 2008 +1000
>  +++ b/include/linux/if_tun.h    Fri Apr 18 06:07:21 2008 +1000
>  @@ -43,6 +43,7 @@
>   #define TUNSETLINK    _IOW('T', 205, int)
>   #define TUNSETGROUP   _IOW('T', 206, int)
>   #define TUNSETRECVVRING _IOW('T', 207, int)
>  +#define TUNSETXMITVRING _IOW('T', 208, int)
>
>   /* TUNSETIFF ifr flags */
>   #define IFF_TUN                0x0001
>  _______________________________________________
>  Virtualization mailing list
>  Virtualization@...ts.linux-foundation.org
>  https://lists.linux-foundation.org/mailman/listinfo/virtualization
>



-- 
Pradeep Singh Rautela
http://eagain.wordpress.com
http://emptydomain.googlepages.com
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