net: make skb_splice_bits more configureable

Prepare skb_splice_bits to be able to deal with AF_UNIX sockets.

AF_UNIX sockets don't use lock_sock/release_sock and thus we have to
use a callback to make the locking and unlocking configureable.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 40 insertions, 21 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f708936cdd23..6b41c15efa27 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -35,6 +35,7 @@
 #include <linux/netdev_features.h>
 #include <linux/sched.h>
 #include <net/flow_dissector.h>
+#include <linux/splice.h>
 
 /* A. Checksumming of received packets by device.
  *
@@ -2699,9 +2700,15 @@ int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
 int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);
 __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset, u8 *to,
                               int len, __wsum csum);
-int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
+ssize_t skb_socket_splice(struct sock *sk,
+                          struct pipe_inode_info *pipe,
+                          struct splice_pipe_desc *spd);
+int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
                     struct pipe_inode_info *pipe, unsigned int len,
-                    unsigned int flags);
+                    unsigned int flags,
+                    ssize_t (*splice_cb)(struct sock *,
+                                         struct pipe_inode_info *,
+                                         struct splice_pipe_desc *));
 void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
 unsigned int skb_zerocopy_headlen(const struct sk_buff *from);
 int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4f2babeaf18d..02769fa4f5c8 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1870,15 +1870,39 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
         return false;
 }
 
+ssize_t skb_socket_splice(struct sock *sk,
+                          struct pipe_inode_info *pipe,
+                          struct splice_pipe_desc *spd)
+{
+        int ret;
+
+        /* Drop the socket lock, otherwise we have reverse
+         * locking dependencies between sk_lock and i_mutex
+         * here as compared to sendfile(). We enter here
+         * with the socket lock held, and splice_to_pipe() will
+         * grab the pipe inode lock. For sendfile() emulation,
+         * we call into ->sendpage() with the i_mutex lock held
+         * and networking will grab the socket lock.
+         */
+        release_sock(sk);
+        ret = splice_to_pipe(pipe, spd);
+        lock_sock(sk);
+
+        return ret;
+}
+
 /*
  * Map data from the skb to a pipe. Should handle both the linear part,
  * the fragments, and the frag list. It does NOT handle frag lists within
  * the frag list, if such a thing exists. We'd probably need to recurse to
  * handle that cleanly.
  */
-int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
+int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
                     struct pipe_inode_info *pipe, unsigned int tlen,
-                    unsigned int flags)
+                    unsigned int flags,
+                    ssize_t (*splice_cb)(struct sock *,
+                                         struct pipe_inode_info *,
+                                         struct splice_pipe_desc *))
 {
         struct partial_page partial[MAX_SKB_FRAGS];
         struct page *pages[MAX_SKB_FRAGS];
@@ -1891,7 +1915,6 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
                 .spd_release = sock_spd_release,
         };
         struct sk_buff *frag_iter;
-        struct sock *sk = skb->sk;
         int ret = 0;
 
         /*
@@ -1914,20 +1937,8 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
         }
 
 done:
-        if (spd.nr_pages) {
-                /*
-                 * Drop the socket lock, otherwise we have reverse
-                 * locking dependencies between sk_lock and i_mutex
-                 * here as compared to sendfile(). We enter here
-                 * with the socket lock held, and splice_to_pipe() will
-                 * grab the pipe inode lock. For sendfile() emulation,
-                 * we call into ->sendpage() with the i_mutex lock held
-                 * and networking will grab the socket lock.
-                 */
-                release_sock(sk);
-                ret = splice_to_pipe(pipe, &spd);
-                lock_sock(sk);
-        }
+        if (spd.nr_pages)
+                ret = splice_cb(sk, pipe, &spd);
 
         return ret;
 }
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 90afcec3f427..65f791f74845 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -695,8 +695,9 @@ static int tcp_splice_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
         struct tcp_splice_state *tss = rd_desc->arg.data;
         int ret;
 
-        ret = skb_splice_bits(skb, offset, tss->pipe, min(rd_desc->count, len),
-                              tss->flags);
+        ret = skb_splice_bits(skb, skb->sk, offset, tss->pipe,
+                              min(rd_desc->count, len), tss->flags,
+                              skb_socket_splice);
         if (ret > 0)
                 rd_desc->count -= ret;
         return ret;