uml: network driver MTU cleanups

A bunch of MTU-related cleanups in the network code.

First, there is the addition of the notion of a maximally-sized packet, which
is the MTU plus headers.  This is used to size the skb that will receive a
packet.  This allows ether_adjust_skb to go away, as it was used to resize the
skb after it was allocated.

Since the skb passed into the low-level read routine is no longer resized, and
possibly reallocated, there, they (and the write routines) don't need to get
an sk_buff **.  They just need the sk_buff * now.  The callers of
ether_adjust_skb still need to do the skb_put, so that's now inlined.

The MAX_PACKET definitions in most of the drivers are gone.

The set_mtu methods were all the same and did nothing, so they can be
removed.

The ethertap driver had a typo which doubled the size of the packet rather
than adding two bytes to it.  It also wasn't defining its setup_size, causing
a zero-byte kmalloc and crash when the invalid pointer returned from kmalloc
was dereferenced.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

19 files changed, 80 insertions, 188 deletions

diff --git a/arch/um/drivers/daemon_kern.c b/arch/um/drivers/daemon_kern.c
index ac507bb87fea..d53ff52bb404 100644
--- a/arch/um/drivers/daemon_kern.c
+++ b/arch/um/drivers/daemon_kern.c
@@ -39,20 +39,15 @@ static void daemon_init(struct net_device *dev, void *data)
         printk("\n");
 }
 
-static int daemon_read(int fd, struct sk_buff **skb,
-                       struct uml_net_private *lp)
+static int daemon_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        *skb = ether_adjust_skb(*skb, ETH_HEADER_OTHER);
-        if (*skb == NULL)
-                return -ENOMEM;
-        return net_recvfrom(fd, skb_mac_header(*skb),
-                            (*skb)->dev->mtu + ETH_HEADER_OTHER);
+        return net_recvfrom(fd, skb_mac_header(skb),
+                            skb->dev->mtu + ETH_HEADER_OTHER);
 }
 
-static int daemon_write(int fd, struct sk_buff **skb,
-                        struct uml_net_private *lp)
+static int daemon_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return daemon_user_write(fd, (*skb)->data, (*skb)->len,
+        return daemon_user_write(fd, skb->data, skb->len,
                                  (struct daemon_data *) &lp->user);
 }
 
diff --git a/arch/um/drivers/daemon_user.c b/arch/um/drivers/daemon_user.c
index 90983d480ac6..f23c109a055c 100644
--- a/arch/um/drivers/daemon_user.c
+++ b/arch/um/drivers/daemon_user.c
@@ -19,8 +19,6 @@
 #include "um_malloc.h"
 #include "user.h"
 
-#define MAX_PACKET (ETH_MAX_PACKET + ETH_HEADER_OTHER)
-
 enum request_type { REQ_NEW_CONTROL };
 
 #define SWITCH_MAGIC 0xfeedface
@@ -184,18 +182,13 @@ int daemon_user_write(int fd, void *buf, int len, struct daemon_data *pri)
         return net_sendto(fd, buf, len, data_addr, sizeof(*data_addr));
 }
 
-static int daemon_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 const struct net_user_info daemon_user_info = {
         .init           = daemon_user_init,
         .open           = daemon_open,
         .close          = NULL,
         .remove         = daemon_remove,
-        .set_mtu        = daemon_set_mtu,
         .add_address    = NULL,
         .delete_address = NULL,
-        .max_packet     = MAX_PACKET - ETH_HEADER_OTHER
+        .mtu            = ETH_MAX_PACKET,
+        .max_packet     = ETH_MAX_PACKET + ETH_HEADER_OTHER,
 };
diff --git a/arch/um/drivers/mcast_kern.c b/arch/um/drivers/mcast_kern.c
index 5027b870d11d..822092f149be 100644
--- a/arch/um/drivers/mcast_kern.c
+++ b/arch/um/drivers/mcast_kern.c
@@ -39,18 +39,15 @@ static void mcast_init(struct net_device *dev, void *data)
                dpri->addr, dpri->port, dpri->ttl);
 }
 
-static int mcast_read(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int mcast_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        *skb = ether_adjust_skb(*skb, ETH_HEADER_OTHER);
-        if (*skb == NULL)
-                return -ENOMEM;
-        return net_recvfrom(fd, skb_mac_header(*skb),
-                            (*skb)->dev->mtu + ETH_HEADER_OTHER);
+        return net_recvfrom(fd, skb_mac_header(skb),
+                            skb->dev->mtu + ETH_HEADER_OTHER);
 }
 
-static int mcast_write(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int mcast_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return mcast_user_write(fd, (*skb)->data, (*skb)->len,
+        return mcast_user_write(fd, skb->data, skb->len,
                                 (struct mcast_data *) &lp->user);
 }
 
diff --git a/arch/um/drivers/mcast_user.c b/arch/um/drivers/mcast_user.c
index e427b5322a36..5f647d7a7292 100644
--- a/arch/um/drivers/mcast_user.c
+++ b/arch/um/drivers/mcast_user.c
@@ -20,8 +20,6 @@
 #include "um_malloc.h"
 #include "user.h"
 
-#define MAX_PACKET (ETH_MAX_PACKET + ETH_HEADER_OTHER)
-
 static struct sockaddr_in *new_addr(char *addr, unsigned short port)
 {
         struct sockaddr_in *sin;
@@ -154,18 +152,13 @@ int mcast_user_write(int fd, void *buf, int len, struct mcast_data *pri)
         return net_sendto(fd, buf, len, data_addr, sizeof(*data_addr));
 }
 
-static int mcast_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 const struct net_user_info mcast_user_info = {
         .init           = mcast_user_init,
         .open           = mcast_open,
         .close          = mcast_close,
         .remove         = mcast_remove,
-        .set_mtu        = mcast_set_mtu,
         .add_address    = NULL,
         .delete_address = NULL,
-        .max_packet     = MAX_PACKET - ETH_HEADER_OTHER
+        .mtu            = ETH_MAX_PACKET,
+        .max_packet     = ETH_MAX_PACKET + ETH_HEADER_OTHER,
 };
diff --git a/arch/um/drivers/net_kern.c b/arch/um/drivers/net_kern.c
index b097a24c1496..59811cc880e0 100644
--- a/arch/um/drivers/net_kern.c
+++ b/arch/um/drivers/net_kern.c
@@ -41,16 +41,16 @@ static int uml_net_rx(struct net_device *dev)
         struct sk_buff *skb;
 
         /* If we can't allocate memory, try again next round. */
-        skb = dev_alloc_skb(dev->mtu);
+        skb = dev_alloc_skb(lp->max_packet);
         if (skb == NULL) {
                 lp->stats.rx_dropped++;
                 return 0;
         }
 
         skb->dev = dev;
-        skb_put(skb, dev->mtu);
+        skb_put(skb, lp->max_packet);
         skb_reset_mac_header(skb);
-        pkt_len = (*lp->read)(lp->fd, &skb, lp);
+        pkt_len = (*lp->read)(lp->fd, skb, lp);
 
         if (pkt_len > 0) {
                 skb_trim(skb, pkt_len);
@@ -178,7 +178,7 @@ static int uml_net_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
         spin_lock_irqsave(&lp->lock, flags);
 
-        len = (*lp->write)(lp->fd, &skb, lp);
+        len = (*lp->write)(lp->fd, skb, lp);
 
         if (len == skb->len) {
                 lp->stats.tx_packets++;
@@ -240,22 +240,9 @@ static int uml_net_set_mac(struct net_device *dev, void *addr)
 
 static int uml_net_change_mtu(struct net_device *dev, int new_mtu)
 {
-        struct uml_net_private *lp = dev->priv;
-        int err = 0;
-
-        spin_lock_irq(&lp->lock);
-
-        new_mtu = (*lp->set_mtu)(new_mtu, &lp->user);
-        if (new_mtu < 0) {
-                err = new_mtu;
-                goto out;
-        }
-
         dev->mtu = new_mtu;
 
- out:
-        spin_unlock_irq(&lp->lock);
-        return err;
+        return 0;
 }
 
 static void uml_net_get_drvinfo(struct net_device *dev,
@@ -427,6 +414,7 @@ static void eth_configure(int n, void *init, char *mac,
                   .dev                  = dev,
                   .fd                   = -1,
                   .mac                  = { 0xfe, 0xfd, 0x0, 0x0, 0x0, 0x0},
+                  .max_packet           = transport->user->max_packet,
                   .protocol             = transport->kern->protocol,
                   .open                 = transport->user->open,
                   .close                = transport->user->close,
@@ -434,8 +422,7 @@ static void eth_configure(int n, void *init, char *mac,
                   .read                 = transport->kern->read,
                   .write                = transport->kern->write,
                   .add_address          = transport->user->add_address,
-                  .delete_address       = transport->user->delete_address,
-                  .set_mtu              = transport->user->set_mtu });
+                  .delete_address       = transport->user->delete_address });
 
         init_timer(&lp->tl);
         spin_lock_init(&lp->lock);
@@ -447,7 +434,7 @@ static void eth_configure(int n, void *init, char *mac,
                 goto out_unregister;
 
         set_ether_mac(dev, device->mac);
-        dev->mtu = transport->user->max_packet;
+        dev->mtu = transport->user->mtu;
         dev->open = uml_net_open;
         dev->hard_start_xmit = uml_net_start_xmit;
         dev->stop = uml_net_close;
@@ -807,19 +794,6 @@ static void close_devices(void)
 
 __uml_exitcall(close_devices);
 
-struct sk_buff *ether_adjust_skb(struct sk_buff *skb, int extra)
-{
-        if ((skb != NULL) && (skb_tailroom(skb) < extra)) {
-                struct sk_buff *skb2;
-
-                skb2 = skb_copy_expand(skb, 0, extra, GFP_ATOMIC);
-                dev_kfree_skb(skb);
-                skb = skb2;
-        }
-        if (skb != NULL) skb_put(skb, extra);
-        return skb;
-}
-
 void iter_addresses(void *d, void (*cb)(unsigned char *, unsigned char *,
                                         void *),
                     void *arg)
diff --git a/arch/um/drivers/pcap_kern.c b/arch/um/drivers/pcap_kern.c
index da0403efbc0d..3a750dd39be1 100644
--- a/arch/um/drivers/pcap_kern.c
+++ b/arch/um/drivers/pcap_kern.c
@@ -31,19 +31,14 @@ void pcap_init(struct net_device *dev, void *data)
         printk("pcap backend, host interface %s\n", ppri->host_if);
 }
 
-static int pcap_read(int fd, struct sk_buff **skb,
-                       struct uml_net_private *lp)
+static int pcap_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        *skb = ether_adjust_skb(*skb, ETH_HEADER_OTHER);
-        if (*skb == NULL)
-                return -ENOMEM;
-
-        return pcap_user_read(fd, skb_mac_header(*skb),
-                              (*skb)->dev->mtu + ETH_HEADER_OTHER,
+        return pcap_user_read(fd, skb_mac_header(skb),
+                              skb->dev->mtu + ETH_HEADER_OTHER,
                               (struct pcap_data *) &lp->user);
 }
 
-static int pcap_write(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int pcap_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
         return -EPERM;
 }
diff --git a/arch/um/drivers/pcap_user.c b/arch/um/drivers/pcap_user.c
index cf996b82af56..e9809356c530 100644
--- a/arch/um/drivers/pcap_user.c
+++ b/arch/um/drivers/pcap_user.c
@@ -13,8 +13,6 @@
 #include "um_malloc.h"
 #include "user.h"
 
-#define MAX_PACKET (ETH_MAX_PACKET + ETH_HEADER_OTHER)
-
 #define PCAP_FD(p) (*(int *)(p))
 
 static int pcap_user_init(void *data, void *dev)
@@ -23,7 +21,8 @@ static int pcap_user_init(void *data, void *dev)
         pcap_t *p;
         char errors[PCAP_ERRBUF_SIZE];
 
-        p = pcap_open_live(pri->host_if, MAX_PACKET, pri->promisc, 0, errors);
+        p = pcap_open_live(pri->host_if, ETH_MAX_PACKET + ETH_HEADER_OTHER,
+                           pri->promisc, 0, errors);
         if (p == NULL) {
                 printk(UM_KERN_ERR "pcap_user_init : pcap_open_live failed - "
                        "'%s'\n", errors);
@@ -133,8 +132,8 @@ const struct net_user_info pcap_user_info = {
         .open           = pcap_open,
         .close          = NULL,
         .remove         = pcap_remove,
-        .set_mtu        = NULL,
         .add_address    = NULL,
         .delete_address = NULL,
-        .max_packet     = MAX_PACKET - ETH_HEADER_OTHER
+        .mtu            = ETH_MAX_PACKET,
+        .max_packet     = ETH_MAX_PACKET + ETH_HEADER_OTHER,
 };
diff --git a/arch/um/drivers/slip_kern.c b/arch/um/drivers/slip_kern.c
index 05ed351de6b5..ae67e7158e71 100644
--- a/arch/um/drivers/slip_kern.c
+++ b/arch/um/drivers/slip_kern.c
@@ -47,17 +47,15 @@ static unsigned short slip_protocol(struct sk_buff *skbuff)
         return htons(ETH_P_IP);
 }
 
-static int slip_read(int fd, struct sk_buff **skb,
-                       struct uml_net_private *lp)
+static int slip_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return slip_user_read(fd, skb_mac_header(*skb), (*skb)->dev->mtu,
+        return slip_user_read(fd, skb_mac_header(skb), skb->dev->mtu,
                               (struct slip_data *) &lp->user);
 }
 
-static int slip_write(int fd, struct sk_buff **skb,
-                      struct uml_net_private *lp)
+static int slip_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return slip_user_write(fd, (*skb)->data, (*skb)->len,
+        return slip_user_write(fd, skb->data, skb->len,
                                (struct slip_data *) &lp->user);
 }
 
diff --git a/arch/um/drivers/slip_user.c b/arch/um/drivers/slip_user.c
index d78f324e7298..5f06204d6871 100644
--- a/arch/um/drivers/slip_user.c
+++ b/arch/um/drivers/slip_user.c
@@ -230,11 +230,6 @@ int slip_user_write(int fd, void *buf, int len, struct slip_data *pri)
         return slip_proto_write(fd, buf, len, &pri->slip);
 }
 
-static int slip_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 static void slip_add_addr(unsigned char *addr, unsigned char *netmask,
                           void *data)
 {
@@ -260,8 +255,8 @@ const struct net_user_info slip_user_info = {
         .open           = slip_open,
         .close          = slip_close,
         .remove         = NULL,
-        .set_mtu        = slip_set_mtu,
         .add_address    = slip_add_addr,
         .delete_address = slip_del_addr,
-        .max_packet     = BUF_SIZE
+        .mtu            = BUF_SIZE,
+        .max_packet     = BUF_SIZE,
 };
diff --git a/arch/um/drivers/slirp_kern.c b/arch/um/drivers/slirp_kern.c
index b208d5e4a405..240ee650865d 100644
--- a/arch/um/drivers/slirp_kern.c
+++ b/arch/um/drivers/slirp_kern.c
@@ -52,18 +52,16 @@ static unsigned short slirp_protocol(struct sk_buff *skbuff)
         return htons(ETH_P_IP);
 }
 
-static int slirp_read(int fd, struct sk_buff **skb,
-                       struct uml_net_private *lp)
+static int slirp_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return slirp_user_read(fd, skb_mac_header(*skb), (*skb)->dev->mtu,
-                              (struct slirp_data *) &lp->user);
+        return slirp_user_read(fd, skb_mac_header(skb), skb->dev->mtu,
+                               (struct slirp_data *) &lp->user);
 }
 
-static int slirp_write(int fd, struct sk_buff **skb,
-                      struct uml_net_private *lp)
+static int slirp_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return slirp_user_write(fd, (*skb)->data, (*skb)->len,
-                               (struct slirp_data *) &lp->user);
+        return slirp_user_write(fd, skb->data, skb->len,
+                                (struct slirp_data *) &lp->user);
 }
 
 const struct net_kern_info slirp_kern_info = {
diff --git a/arch/um/drivers/slirp_user.c b/arch/um/drivers/slirp_user.c
index a4755bc33e1e..1865089ff41a 100644
--- a/arch/um/drivers/slirp_user.c
+++ b/arch/um/drivers/slirp_user.c
@@ -124,18 +124,13 @@ int slirp_user_write(int fd, void *buf, int len, struct slirp_data *pri)
         return slip_proto_write(fd, buf, len, &pri->slip);
 }
 
-static int slirp_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 const struct net_user_info slirp_user_info = {
         .init           = slirp_user_init,
         .open           = slirp_open,
         .close          = slirp_close,
         .remove         = NULL,
-        .set_mtu        = slirp_set_mtu,
         .add_address    = NULL,
         .delete_address = NULL,
-        .max_packet     = BUF_SIZE
+        .mtu            = BUF_SIZE,
+        .max_packet     = BUF_SIZE,
 };
diff --git a/arch/um/drivers/vde_kern.c b/arch/um/drivers/vde_kern.c
index c5d01685d2b5..add7e722defb 100644
--- a/arch/um/drivers/vde_kern.c
+++ b/arch/um/drivers/vde_kern.c
@@ -36,30 +36,25 @@ static void vde_init(struct net_device *dev, void *data)
         printk("\n");
 }
 
-static int vde_read(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int vde_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
         struct vde_data *pri = (struct vde_data *) &lp->user;
 
-        if (pri->conn != NULL) {
-                *skb = ether_adjust_skb(*skb, ETH_HEADER_OTHER);
-                if (*skb == NULL)
-                        return -ENOMEM;
-
-                return vde_user_read(pri->conn, skb_mac_header(*skb),
-                                     (*skb)->dev->mtu + ETH_HEADER_OTHER);
-        }
+        if (pri->conn != NULL)
+                return vde_user_read(pri->conn, skb_mac_header(skb),
+                                     skb->dev->mtu + ETH_HEADER_OTHER);
 
         printk(KERN_ERR "vde_read - we have no VDECONN to read from");
         return -EBADF;
 }
 
-static int vde_write(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int vde_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
         struct vde_data *pri = (struct vde_data *) &lp->user;
 
         if (pri->conn != NULL)
-                return vde_user_write((void *)pri->conn, (*skb)->data,
-                                      (*skb)->len);
+                return vde_user_write((void *)pri->conn, skb->data,
+                                      skb->len);
 
         printk(KERN_ERR "vde_write - we have no VDECONN to write to");
         return -EBADF;
diff --git a/arch/um/drivers/vde_user.c b/arch/um/drivers/vde_user.c
index 7533cd3cbba4..d9941fe5f931 100644
--- a/arch/um/drivers/vde_user.c
+++ b/arch/um/drivers/vde_user.c
@@ -12,8 +12,6 @@
 #include "user.h"
 #include "vde.h"
 
-#define MAX_PACKET (ETH_MAX_PACKET + ETH_HEADER_OTHER)
-
 static int vde_user_init(void *data, void *dev)
 {
         struct vde_data *pri = data;
@@ -65,20 +63,15 @@ static void vde_remove(void *data)
         printk(UM_KERN_WARNING "vde_remove - we have no VDECONN to remove");
 }
 
-static int vde_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 const struct net_user_info vde_user_info = {
         .init           = vde_user_init,
         .open           = vde_user_open,
         .close          = NULL,
         .remove         = vde_remove,
-        .set_mtu        = vde_set_mtu,
         .add_address    = NULL,
         .delete_address = NULL,
-        .max_packet     = MAX_PACKET - ETH_HEADER_OTHER
+        .mtu            = ETH_MAX_PACKET,
+        .max_packet     = ETH_MAX_PACKET + ETH_HEADER_OTHER,
 };
 
 void vde_init_libstuff(struct vde_data *vpri, struct vde_init *init)
diff --git a/arch/um/include/net_kern.h b/arch/um/include/net_kern.h
index 9237056b9103..d843c7924a7c 100644
--- a/arch/um/include/net_kern.h
+++ b/arch/um/include/net_kern.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ * Copyright (C) 2002 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */
 
@@ -30,24 +30,24 @@ struct uml_net_private {
         struct work_struct work;
         int fd;
         unsigned char mac[ETH_ALEN];
+        int max_packet;
         unsigned short (*protocol)(struct sk_buff *);
         int (*open)(void *);
         void (*close)(int, void *);
         void (*remove)(void *);
-        int (*read)(int, struct sk_buff **skb, struct uml_net_private *);
-        int (*write)(int, struct sk_buff **skb, struct uml_net_private *);
+        int (*read)(int, struct sk_buff *skb, struct uml_net_private *);
+        int (*write)(int, struct sk_buff *skb, struct uml_net_private *);
 
         void (*add_address)(unsigned char *, unsigned char *, void *);
         void (*delete_address)(unsigned char *, unsigned char *, void *);
-        int (*set_mtu)(int mtu, void *);
         char user[0];
 };
 
 struct net_kern_info {
         void (*init)(struct net_device *, void *);
         unsigned short (*protocol)(struct sk_buff *);
-        int (*read)(int, struct sk_buff **skb, struct uml_net_private *);
-        int (*write)(int, struct sk_buff **skb, struct uml_net_private *);
+        int (*read)(int, struct sk_buff *skb, struct uml_net_private *);
+        int (*write)(int, struct sk_buff *skb, struct uml_net_private *);
 };
 
 struct transport {
@@ -62,7 +62,6 @@ struct transport {
 
 extern struct net_device *ether_init(int);
 extern unsigned short ether_protocol(struct sk_buff *);
-extern struct sk_buff *ether_adjust_skb(struct sk_buff *skb, int extra);
 extern int tap_setup_common(char *str, char *type, char **dev_name,
                             char **mac_out, char **gate_addr);
 extern void register_transport(struct transport *new);
diff --git a/arch/um/include/net_user.h b/arch/um/include/net_user.h
index cfe7c50634b9..63bee158cd8e 100644
--- a/arch/um/include/net_user.h
+++ b/arch/um/include/net_user.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */
 
@@ -18,10 +18,10 @@ struct net_user_info {
         int (*open)(void *);
         void (*close)(int, void *);
         void (*remove)(void *);
-        int (*set_mtu)(int mtu, void *);
         void (*add_address)(unsigned char *, unsigned char *, void *);
         void (*delete_address)(unsigned char *, unsigned char *, void *);
         int max_packet;
+        int mtu;
 };
 
 extern void ether_user_init(void *data, void *dev);
diff --git a/arch/um/os-Linux/drivers/ethertap_kern.c b/arch/um/os-Linux/drivers/ethertap_kern.c
index 542bcc58354c..04f11b9f1ac0 100644
--- a/arch/um/os-Linux/drivers/ethertap_kern.c
+++ b/arch/um/os-Linux/drivers/ethertap_kern.c
@@ -36,35 +36,24 @@ static void etap_init(struct net_device *dev, void *data)
         printk("\n");
 }
 
-static int etap_read(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int etap_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
         int len;
 
-        *skb = ether_adjust_skb(*skb, ETH_HEADER_ETHERTAP);
-        if (*skb == NULL)
-                return -ENOMEM;
-        len = net_recvfrom(fd, skb_mac_header(*skb),
-                           (*skb)->dev->mtu + 2 * ETH_HEADER_ETHERTAP);
+        len = net_recvfrom(fd, skb_mac_header(skb),
+                           skb->dev->mtu + 2 + ETH_HEADER_ETHERTAP);
         if (len <= 0)
-                return len;
-        skb_pull(*skb, 2);
+                return(len);
+
+        skb_pull(skb, 2);
         len -= 2;
         return len;
 }
 
-static int etap_write(int fd, struct sk_buff **skb, struct uml_net_private *lp)
+static int etap_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        if (skb_headroom(*skb) < 2) {
-                struct sk_buff *skb2;
-
-                skb2 = skb_realloc_headroom(*skb, 2);
-                dev_kfree_skb(*skb);
-                if (skb2 == NULL)
-                        return -ENOMEM;
-                *skb = skb2;
-        }
-        skb_push(*skb, 2);
-        return net_send(fd, (*skb)->data, (*skb)->len);
+        skb_push(skb, 2);
+        return net_send(fd, skb->data, skb->len);
 }
 
 const struct net_kern_info ethertap_kern_info = {
@@ -99,6 +88,7 @@ static struct transport ethertap_transport = {
         .user           = &ethertap_user_info,
         .kern           = &ethertap_kern_info,
         .private_size   = sizeof(struct ethertap_data),
+        .setup_size     = sizeof(struct ethertap_init),
 };
 
 static int register_ethertap(void)
diff --git a/arch/um/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
index 29404b955f18..4ff553603449 100644
--- a/arch/um/os-Linux/drivers/ethertap_user.c
+++ b/arch/um/os-Linux/drivers/ethertap_user.c
@@ -222,11 +222,6 @@ static void etap_close(int fd, void *data)
         pri->control_fd = -1;
 }
 
-static int etap_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 static void etap_add_addr(unsigned char *addr, unsigned char *netmask,
                           void *data)
 {
@@ -254,8 +249,8 @@ const struct net_user_info ethertap_user_info = {
         .open           = etap_open,
         .close          = etap_close,
         .remove         = NULL,
-        .set_mtu        = etap_set_mtu,
         .add_address    = etap_add_addr,
         .delete_address = etap_del_addr,
-        .max_packet     = MAX_PACKET - ETH_HEADER_ETHERTAP
+        .mtu            = ETH_MAX_PACKET,
+        .max_packet     = ETH_MAX_PACKET + ETH_HEADER_ETHERTAP,
 };
diff --git a/arch/um/os-Linux/drivers/tuntap_kern.c b/arch/um/os-Linux/drivers/tuntap_kern.c
index 9ade1f892ac8..9d384807b077 100644
--- a/arch/um/os-Linux/drivers/tuntap_kern.c
+++ b/arch/um/os-Linux/drivers/tuntap_kern.c
@@ -35,20 +35,15 @@ static void tuntap_init(struct net_device *dev, void *data)
         printk("\n");
 }
 
-static int tuntap_read(int fd, struct sk_buff **skb,
-                       struct uml_net_private *lp)
+static int tuntap_read(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        *skb = ether_adjust_skb(*skb, ETH_HEADER_OTHER);
-        if (*skb == NULL)
-                return -ENOMEM;
-        return net_read(fd, skb_mac_header(*skb),
-                        (*skb)->dev->mtu + ETH_HEADER_OTHER);
+        return net_read(fd, skb_mac_header(skb),
+                        skb->dev->mtu + ETH_HEADER_OTHER);
 }
 
-static int tuntap_write(int fd, struct sk_buff **skb,
-                        struct uml_net_private *lp)
+static int tuntap_write(int fd, struct sk_buff *skb, struct uml_net_private *lp)
 {
-        return net_write(fd, (*skb)->data, (*skb)->len);
+        return net_write(fd, skb->data, skb->len);
 }
 
 const struct net_kern_info tuntap_kern_info = {
diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index 10714a413cfd..6c55d3c8ead8 100644
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -18,8 +18,6 @@
 #include "tuntap.h"
 #include "user.h"
 
-#define MAX_PACKET ETH_MAX_PACKET
-
 static int tuntap_user_init(void *data, void *dev)
 {
         struct tuntap_data *pri = data;
@@ -206,18 +204,13 @@ static void tuntap_close(int fd, void *data)
         pri->fd = -1;
 }
 
-static int tuntap_set_mtu(int mtu, void *data)
-{
-        return mtu;
-}
-
 const struct net_user_info tuntap_user_info = {
         .init           = tuntap_user_init,
         .open           = tuntap_open,
         .close          = tuntap_close,
         .remove         = NULL,
-        .set_mtu        = tuntap_set_mtu,
         .add_address    = tuntap_add_addr,
         .delete_address = tuntap_del_addr,
-        .max_packet     = MAX_PACKET
+        .mtu            = ETH_MAX_PACKET,
+        .max_packet     = ETH_MAX_PACKET + ETH_HEADER_OTHER,
 };