[PATCH 5/6] net/core: support compiling out splice

[PATCH 5/6] net/core: support compiling out splice

[Pieter Smith]

Compile out splice support from networking core when the splice-family of
syscalls is not supported by the system (i.e. CONFIG_SYSCALL_SPLICE is
undefined).

Signed-off-by: Pieter Smith <pieter@boesman.nl>
---
 include/linux/skbuff.h | 9 +++++++++
 net/core/skbuff.c      | 9 ++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index a59d934..8c28524 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2640,9 +2640,18 @@ 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);
+#ifdef CONFIG_SYSCALL_SPLICE
 int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
 		    struct pipe_inode_info *pipe, unsigned int len,
 		    unsigned int flags);
+#else /* #ifdef CONFIG_SYSCALL_SPLICE */
+static inline int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
+		    struct pipe_inode_info *pipe, unsigned int len,
+		    unsigned int flags)
+{
+	return -EPERM;
+}
+#endif /* #ifdef CONFIG_SYSCALL_SPLICE */
 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 61059a0..74fad8a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1781,9 +1781,9 @@ static bool __splice_segment(struct page *page, unsigned int poff,
  * Map linear and fragment data from the skb to spd. It reports true if the
  * pipe is full or if we already spliced the requested length.
  */
-static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
-			      unsigned int *offset, unsigned int *len,
-			      struct splice_pipe_desc *spd, struct sock *sk)
+static bool __maybe_unused __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
+					     unsigned int *offset, unsigned int *len,
+					     struct splice_pipe_desc *spd, struct sock *sk)
 {
 	int seg;
 
@@ -1821,6 +1821,7 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
  * the frag list, if such a thing exists. We'd probably need to recurse to
  * handle that cleanly.
  */
+#ifdef CONFIG_SYSCALL_SPLICE
 int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
 		    struct pipe_inode_info *pipe, unsigned int tlen,
 		    unsigned int flags)
@@ -1876,6 +1877,8 @@ done:
 
 	return ret;
 }
+#endif /* #ifdef CONFIG_SYSCALL_SPLICE */
+
 
 /**
  *	skb_store_bits - store bits from kernel buffer to skb
-- 
1.9.1

Re: [PATCH 5/6] net/core: support compiling out splice

[Josh Triplett]

On Sat, Nov 22, 2014 at 10:00:00PM +0100, Pieter Smith wrote:
> Compile out splice support from networking core when the splice-family of
> syscalls is not supported by the system (i.e. CONFIG_SYSCALL_SPLICE is
> undefined).

Please explain in the commit message why this particular bit of splice
support needs compiling out when most other bits do not.

Also, a couple of style comments below.

> Signed-off-by: Pieter Smith <pieter@boesman.nl>
> ---
>  include/linux/skbuff.h | 9 +++++++++
>  net/core/skbuff.c      | 9 ++++++---
>  2 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index a59d934..8c28524 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2640,9 +2640,18 @@ 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);
> +#ifdef CONFIG_SYSCALL_SPLICE
>  int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
>  		    struct pipe_inode_info *pipe, unsigned int len,
>  		    unsigned int flags);
> +#else /* #ifdef CONFIG_SYSCALL_SPLICE */
> +static inline int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
> +		    struct pipe_inode_info *pipe, unsigned int len,
> +		    unsigned int flags)
> +{
> +	return -EPERM;
> +}
> +#endif /* #ifdef CONFIG_SYSCALL_SPLICE */

These comments, and the one added below in the corresponding .c file,
don't match the prevailing style.  These are so short (fitting on one
screen) that they hardly seem worth the comments at all, but if you want
to include them, s/#ifdef// in the comment.

>  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 61059a0..74fad8a 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1781,9 +1781,9 @@ static bool __splice_segment(struct page *page, unsigned int poff,
>   * Map linear and fragment data from the skb to spd. It reports true if the
>   * pipe is full or if we already spliced the requested length.
>   */
> -static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
> -			      unsigned int *offset, unsigned int *len,
> -			      struct splice_pipe_desc *spd, struct sock *sk)
> +static bool __maybe_unused __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
> +					     unsigned int *offset, unsigned int *len,
> +					     struct splice_pipe_desc *spd, struct sock *sk)
>  {
>  	int seg;
>  
> @@ -1821,6 +1821,7 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
>   * the frag list, if such a thing exists. We'd probably need to recurse to
>   * handle that cleanly.
>   */
> +#ifdef CONFIG_SYSCALL_SPLICE
>  int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
>  		    struct pipe_inode_info *pipe, unsigned int tlen,
>  		    unsigned int flags)
> @@ -1876,6 +1877,8 @@ done:
>  
>  	return ret;
>  }
> +#endif /* #ifdef CONFIG_SYSCALL_SPLICE */
> +

This extra blank line shouldn't be here.

>  /**
>   *	skb_store_bits - store bits from kernel buffer to skb
> -- 
> 1.9.1
> 

Re: [PATCH 5/6] net/core: support compiling out splice

[Josh Triplett]

[Please don't top-post.]

On Sat, Nov 22, 2014 at 11:50:51PM +0100, Pieter Smith wrote:
> splice exports a structure that is used by skbuf. Mocking out a function is
> straightforward. To my knowledge there is no elegant way of mocking out a
> splice_operations struct. I directly modified the code to prevent linking
> against the struct. Do you know of a better technique to get the same
> result?

No, I don't.  The approach you took seems fine; I'm just saying that you
need to explain the need for it in the commit message.

- JosH Triplett

[PATCH 5/6] net/core: support compiling out splice

[Pieter Smith]

To implement splice support, net/core makes use of nosteal_pipe_buf_ops. This
struct is exported by fs/splice. The goal of the larger patch set is to
completely compile out fs/splice, so uses of the exported struct need to be
compiled out along with fs/splice.

This patch therefore compiles out splice support in net/core when
CONFIG_SYSCALL_SPLICE is undefined. The compiled out function skb_splice_bits
is transparently mocked out with a static inline. The greater patch set removes
userspace splice support so it cannot be called anyway.

Signed-off-by: Pieter Smith <pieter-qeJ+1H9vRZbz+pZb47iToQ@public.gmane.org>
---
 include/linux/skbuff.h | 9 +++++++++
 net/core/skbuff.c      | 9 ++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index a59d934..54a50c1 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2640,9 +2640,18 @@ 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);
+#ifdef CONFIG_SYSCALL_SPLICE
 int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
 		    struct pipe_inode_info *pipe, unsigned int len,
 		    unsigned int flags);
+#else
+static inline int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
+		    struct pipe_inode_info *pipe, unsigned int len,
+		    unsigned int flags)
+{
+	return -EPERM;
+}
+#endif
 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 61059a0..74fad8a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1781,9 +1781,9 @@ static bool __splice_segment(struct page *page, unsigned int poff,
  * Map linear and fragment data from the skb to spd. It reports true if the
  * pipe is full or if we already spliced the requested length.
  */
-static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
-			      unsigned int *offset, unsigned int *len,
-			      struct splice_pipe_desc *spd, struct sock *sk)
+static bool __maybe_unused __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
+					     unsigned int *offset, unsigned int *len,
+					     struct splice_pipe_desc *spd, struct sock *sk)
 {
 	int seg;
 
@@ -1821,6 +1821,7 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
  * the frag list, if such a thing exists. We'd probably need to recurse to
  * handle that cleanly.
  */
+#ifdef CONFIG_SYSCALL_SPLICE
 int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
 		    struct pipe_inode_info *pipe, unsigned int tlen,
 		    unsigned int flags)
@@ -1876,6 +1877,8 @@ done:
 
 	return ret;
 }
+#endif /* #ifdef CONFIG_SYSCALL_SPLICE */
+
 
 /**
  *	skb_store_bits - store bits from kernel buffer to skb
-- 
2.1.0


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