[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 0/6] kernel tinification: optionally compile out splice family of syscalls (splice, vmsplice, tee and sendfile)

[Pieter Smith]

REPO: https://github.com/smipi1/linux-tinification.git

BRANCH: tiny/config-syscall-splice

BACKGROUND: This patch-set forms part of the Linux Kernel Tinification effort (
  https://tiny.wiki.kernel.org/).

GOAL: Support compiling out the splice family of syscalls (splice, vmsplice,
  tee and sendfile) along with all supporting infrastructure if not needed.
  Many embedded systems will not need the splice-family syscalls. Omitting them
  saves space.

STRATEGY:
a. With the goal of eventually compiling out fs/splice.c, several functions
   that are only used in support of the the splice family of syscalls are moved
   into fs/splice.c from fs/read_write.c. The kernel_write function that is not
   used to support the splice syscalls is moved to fs/read_write.c:
     0001-fs-move-sendfile-syscall-into-fs-splice.patch
     0002-fs-moved-kernel_write-to-fs-read_write.patch

b. Introduce an EXPERT kernel configuration option; CONFIG_SYSCALL_SPLICE; to
   compile out the splice family of syscalls. This removes all userspace uses
   of the splice infrastructure.
     0003-fs-splice-support-compiling-out-splice-family-syscal.patch

c. Splice exports an operations struct, nosteal_pipe_buf_ops. Eliminate the 
   use of this struct when CONFIG_SYSCALL_SPLICE is undefined, so that splice
   can later be compiled out:
     0004-fs-fuse-support-compiling-out-splice.patch
     0005-net-core-support-compiling-out-splice.patch

e. Compile out fs/splice.c. Functions exported by fs/splice are mocked out with
   failing static inlines. This is done so as to all but eliminate the
   maintenance burden on file-system drivers.
     0006-fs-splice-full-support-for-compiling-out-splice.patch

RESULTS: A tinyconfig bloat-o-meter score for the entire patch-set:

add/remove: 0/41 grow/shrink: 5/7 up/down: 23/-8422 (-8399)
function                                     old     new   delta
sys_pwritev                                  115     122      +7
sys_preadv                                   115     122      +7
fdput_pos                                     29      36      +7
sys_pwrite64                                 115     116      +1
sys_pread64                                  115     116      +1
pipe_to_null                                   4       -      -4
generic_pipe_buf_nosteal                       6       -      -6
spd_release_page                              10       -     -10
fdput                                         11       -     -11
PageUptodate                                  22      11     -11
lock_page                                     36      24     -12
signal_pending                                39      26     -13
fdget                                         56      42     -14
page_cache_pipe_buf_release                   16       -     -16
user_page_pipe_buf_ops                        20       -     -20
splice_write_null                             24       4     -20
page_cache_pipe_buf_ops                       20       -     -20
nosteal_pipe_buf_ops                          20       -     -20
default_pipe_buf_ops                          20       -     -20
generic_splice_sendpage                       24       -     -24
user_page_pipe_buf_steal                      25       -     -25
splice_shrink_spd                             27       -     -27
pipe_to_user                                  43       -     -43
direct_splice_actor                           47       -     -47
default_file_splice_write                     49       -     -49
wakeup_pipe_writers                           54       -     -54
wakeup_pipe_readers                           54       -     -54
write_pipe_buf                                71       -     -71
page_cache_pipe_buf_confirm                   80       -     -80
splice_grow_spd                               87       -     -87
do_splice_to                                  87       -     -87
ipipe_prep.part                               92       -     -92
splice_from_pipe                              93       -     -93
splice_from_pipe_next                        107       -    -107
pipe_to_sendpage                             109       -    -109
page_cache_pipe_buf_steal                    114       -    -114
opipe_prep.part                              119       -    -119
sys_sendfile                                 122       -    -122
generic_file_splice_read                     131       8    -123
sys_sendfile64                               126       -    -126
sys_vmsplice                                 137       -    -137
do_splice_direct                             148       -    -148
vmsplice_to_user                             205       -    -205
__splice_from_pipe                           246       -    -246
splice_direct_to_actor                       348       -    -348
splice_to_pipe                               371       -    -371
do_sendfile                                  492       -    -492
sys_tee                                      497       -    -497
vmsplice_to_pipe                             558       -    -558
default_file_splice_read                     688       -    -688
iter_file_splice_write                       702       4    -698
sys_splice                                  1075       -   -1075
__generic_file_splice_read                  1109       -   -1109

Pieter Smith (6):
  fs: move sendfile syscall into fs/splice
  fs: moved kernel_write to fs/read_write
  fs/splice: support compiling out splice-family syscalls
  fs/fuse: support compiling out splice
  net/core: support compiling out splice
  fs/splice: full support for compiling out splice

 fs/Makefile            |   3 +-
 fs/fuse/dev.c          |   4 +-
 fs/read_write.c        | 181 +++------------------------------------------
 fs/splice.c            | 194 +++++++++++++++++++++++++++++++++++++++++++++----
 include/linux/fs.h     |  32 ++++++++
 include/linux/skbuff.h |   9 +++
 include/linux/splice.h |  42 +++++++++++
 init/Kconfig           |  10 +++
 kernel/sys_ni.c        |   8 ++
 net/core/skbuff.c      |   9 ++-
 10 files changed, 300 insertions(+), 192 deletions(-)

-- 
2.1.0

[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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