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>

4 files changed, 19 insertions, 46 deletions

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,
 };