[PATCH v6 0/7] kernel tinification: optionally compile out splice family of syscalls (splice, vmsplice, tee and sendfile)

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.

HISTORY:
  PATCH v6:
    - Removed unnecessary addition of __maybe_unused in fs/fuse

  PATCH v5:
    - Fix up commit log still referring to dropped __splice_p()

  PATCH v4:
    - Drops __splice_p()
    - Let nfsd fall back to non-splice support when splice is compiled out
    - Style fixes
  
  PATCH v3:
    - Fixup commit logs so that they are consistent with patch strategy
    - Style fixes
  
  PATCH v2:
    - Avoid the ifdef mess introduced in PATCH v1 by mocking out exported splice
      functions.

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.

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.

c. Splice exports an operations struct, nosteal_pipe_buf_ops. Eliminate the 
   uses of this struct when CONFIG_SYSCALL_SPLICE is undefined, so that splice
   can later be compiled out.

d. Let nfsd fall back to non-splice support when splice is compiled out.

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.

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 (7):
  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/nfsd: 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     |  26 +++++++
 include/linux/skbuff.h |  10 +++
 include/linux/splice.h |  42 +++++++++++
 init/Kconfig           |  10 +++
 kernel/sys_ni.c        |   8 ++
 net/core/skbuff.c      |  11 ++-
 net/sunrpc/svc.c       |   2 +-
 11 files changed, 299 insertions(+), 192 deletions(-)

-- 
2.1.0

sendfile functionally forms part of the splice group of syscalls (splice,
vmsplice and tee). Grouping sendfile with splice paves the way to compiling out
the splice group of syscalls for embedded systems that do not need these.

add/remove: 0/0 grow/shrink: 7/2 up/down: 86/-61 (25)
function                                     old     new   delta
file_start_write                              34      68     +34
file_end_write                                29      58     +29
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
sys_tee                                      497     491      -6
sys_splice                                  1075    1020     -55

Signed-off-by: Pieter Smith <redacted>
---
 fs/read_write.c | 175 -------------------------------------------------------
 fs/splice.c     | 178 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 178 insertions(+), 175 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 7d9318c..d9451ba 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c

@@ -1191,178 +1191,3 @@ COMPAT_SYSCALL_DEFINE5(pwritev, compat_ulong_t, fd,
 }
 #endif
 
-static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
-		  	   size_t count, loff_t max)
-{
-	struct fd in, out;
-	struct inode *in_inode, *out_inode;
-	loff_t pos;
-	loff_t out_pos;
-	ssize_t retval;
-	int fl;
-
-	/*
-	 * Get input file, and verify that it is ok..
-	 */
-	retval = -EBADF;
-	in = fdget(in_fd);
-	if (!in.file)
-		goto out;
-	if (!(in.file->f_mode & FMODE_READ))
-		goto fput_in;
-	retval = -ESPIPE;
-	if (!ppos) {
-		pos = in.file->f_pos;
-	} else {
-		pos = *ppos;
-		if (!(in.file->f_mode & FMODE_PREAD))
-			goto fput_in;
-	}
-	retval = rw_verify_area(READ, in.file, &pos, count);
-	if (retval < 0)
-		goto fput_in;
-	count = retval;
-
-	/*
-	 * Get output file, and verify that it is ok..
-	 */
-	retval = -EBADF;
-	out = fdget(out_fd);
-	if (!out.file)
-		goto fput_in;
-	if (!(out.file->f_mode & FMODE_WRITE))
-		goto fput_out;
-	retval = -EINVAL;
-	in_inode = file_inode(in.file);
-	out_inode = file_inode(out.file);
-	out_pos = out.file->f_pos;
-	retval = rw_verify_area(WRITE, out.file, &out_pos, count);
-	if (retval < 0)
-		goto fput_out;
-	count = retval;
-
-	if (!max)
-		max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
-
-	if (unlikely(pos + count > max)) {
-		retval = -EOVERFLOW;
-		if (pos >= max)
-			goto fput_out;
-		count = max - pos;
-	}
-
-	fl = 0;
-#if 0
-	/*
-	 * We need to debate whether we can enable this or not. The
-	 * man page documents EAGAIN return for the output at least,
-	 * and the application is arguably buggy if it doesn't expect
-	 * EAGAIN on a non-blocking file descriptor.
-	 */
-	if (in.file->f_flags & O_NONBLOCK)
-		fl = SPLICE_F_NONBLOCK;
-#endif
-	file_start_write(out.file);
-	retval = do_splice_direct(in.file, &pos, out.file, &out_pos, count, fl);
-	file_end_write(out.file);
-
-	if (retval > 0) {
-		add_rchar(current, retval);
-		add_wchar(current, retval);
-		fsnotify_access(in.file);
-		fsnotify_modify(out.file);
-		out.file->f_pos = out_pos;
-		if (ppos)
-			*ppos = pos;
-		else
-			in.file->f_pos = pos;
-	}
-
-	inc_syscr(current);
-	inc_syscw(current);
-	if (pos > max)
-		retval = -EOVERFLOW;
-
-fput_out:
-	fdput(out);
-fput_in:
-	fdput(in);
-out:
-	return retval;
-}
-
-SYSCALL_DEFINE4(sendfile, int, out_fd, int, in_fd, off_t __user *, offset, size_t, count)
-{
-	loff_t pos;
-	off_t off;
-	ssize_t ret;
-
-	if (offset) {
-		if (unlikely(get_user(off, offset)))
-			return -EFAULT;
-		pos = off;
-		ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
-		if (unlikely(put_user(pos, offset)))
-			return -EFAULT;
-		return ret;
-	}
-
-	return do_sendfile(out_fd, in_fd, NULL, count, 0);
-}
-
-SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd, loff_t __user *, offset, size_t, count)
-{
-	loff_t pos;
-	ssize_t ret;
-
-	if (offset) {
-		if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
-			return -EFAULT;
-		ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
-		if (unlikely(put_user(pos, offset)))
-			return -EFAULT;
-		return ret;
-	}
-
-	return do_sendfile(out_fd, in_fd, NULL, count, 0);
-}
-
-#ifdef CONFIG_COMPAT
-COMPAT_SYSCALL_DEFINE4(sendfile, int, out_fd, int, in_fd,
-		compat_off_t __user *, offset, compat_size_t, count)
-{
-	loff_t pos;
-	off_t off;
-	ssize_t ret;
-
-	if (offset) {
-		if (unlikely(get_user(off, offset)))
-			return -EFAULT;
-		pos = off;
-		ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
-		if (unlikely(put_user(pos, offset)))
-			return -EFAULT;
-		return ret;
-	}
-
-	return do_sendfile(out_fd, in_fd, NULL, count, 0);
-}
-
-COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
-		compat_loff_t __user *, offset, compat_size_t, count)
-{
-	loff_t pos;
-	ssize_t ret;
-
-	if (offset) {
-		if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
-			return -EFAULT;
-		ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
-		if (unlikely(put_user(pos, offset)))
-			return -EFAULT;
-		return ret;
-	}
-
-	return do_sendfile(out_fd, in_fd, NULL, count, 0);
-}
-#endif

diff --git a/fs/splice.c b/fs/splice.c
index f5cb9ba..c1a2861 100644
--- a/fs/splice.c
+++ b/fs/splice.c

@@ -28,6 +28,7 @@
 #include <linux/export.h>
 #include <linux/syscalls.h>
 #include <linux/uio.h>
+#include <linux/fsnotify.h>
 #include <linux/security.h>
 #include <linux/gfp.h>
 #include <linux/socket.h>

@@ -2039,3 +2040,180 @@ SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
 
 	return error;
 }
+
+static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
+			   size_t count, loff_t max)
+{
+	struct fd in, out;
+	struct inode *in_inode, *out_inode;
+	loff_t pos;
+	loff_t out_pos;
+	ssize_t retval;
+	int fl;
+
+	/*
+	 * Get input file, and verify that it is ok..
+	 */
+	retval = -EBADF;
+	in = fdget(in_fd);
+	if (!in.file)
+		goto out;
+	if (!(in.file->f_mode & FMODE_READ))
+		goto fput_in;
+	retval = -ESPIPE;
+	if (!ppos) {
+		pos = in.file->f_pos;
+	} else {
+		pos = *ppos;
+		if (!(in.file->f_mode & FMODE_PREAD))
+			goto fput_in;
+	}
+	retval = rw_verify_area(READ, in.file, &pos, count);
+	if (retval < 0)
+		goto fput_in;
+	count = retval;
+
+	/*
+	 * Get output file, and verify that it is ok..
+	 */
+	retval = -EBADF;
+	out = fdget(out_fd);
+	if (!out.file)
+		goto fput_in;
+	if (!(out.file->f_mode & FMODE_WRITE))
+		goto fput_out;
+	retval = -EINVAL;
+	in_inode = file_inode(in.file);
+	out_inode = file_inode(out.file);
+	out_pos = out.file->f_pos;
+	retval = rw_verify_area(WRITE, out.file, &out_pos, count);
+	if (retval < 0)
+		goto fput_out;
+	count = retval;
+
+	if (!max)
+		max = min(in_inode->i_sb->s_maxbytes, out_inode->i_sb->s_maxbytes);
+
+	if (unlikely(pos + count > max)) {
+		retval = -EOVERFLOW;
+		if (pos >= max)
+			goto fput_out;
+		count = max - pos;
+	}
+
+	fl = 0;
+#if 0
+	/*
+	 * We need to debate whether we can enable this or not. The
+	 * man page documents EAGAIN return for the output at least,
+	 * and the application is arguably buggy if it doesn't expect
+	 * EAGAIN on a non-blocking file descriptor.
+	 */
+	if (in.file->f_flags & O_NONBLOCK)
+		fl = SPLICE_F_NONBLOCK;
+#endif
+	file_start_write(out.file);
+	retval = do_splice_direct(in.file, &pos, out.file, &out_pos, count, fl);
+	file_end_write(out.file);
+
+	if (retval > 0) {
+		add_rchar(current, retval);
+		add_wchar(current, retval);
+		fsnotify_access(in.file);
+		fsnotify_modify(out.file);
+		out.file->f_pos = out_pos;
+		if (ppos)
+			*ppos = pos;
+		else
+			in.file->f_pos = pos;
+	}
+
+	inc_syscr(current);
+	inc_syscw(current);
+	if (pos > max)
+		retval = -EOVERFLOW;
+
+fput_out:
+	fdput(out);
+fput_in:
+	fdput(in);
+out:
+	return retval;
+}
+
+SYSCALL_DEFINE4(sendfile, int, out_fd, int, in_fd, off_t __user *, offset, size_t, count)
+{
+	loff_t pos;
+	off_t off;
+	ssize_t ret;
+
+	if (offset) {
+		if (unlikely(get_user(off, offset)))
+			return -EFAULT;
+		pos = off;
+		ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
+		if (unlikely(put_user(pos, offset)))
+			return -EFAULT;
+		return ret;
+	}
+
+	return do_sendfile(out_fd, in_fd, NULL, count, 0);
+}
+
+SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd, loff_t __user *, offset, size_t, count)
+{
+	loff_t pos;
+	ssize_t ret;
+
+	if (offset) {
+		if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
+			return -EFAULT;
+		ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
+		if (unlikely(put_user(pos, offset)))
+			return -EFAULT;
+		return ret;
+	}
+
+	return do_sendfile(out_fd, in_fd, NULL, count, 0);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE4(sendfile, int, out_fd, int, in_fd,
+		compat_off_t __user *, offset, compat_size_t, count)
+{
+	loff_t pos;
+	off_t off;
+	ssize_t ret;
+
+	if (offset) {
+		if (unlikely(get_user(off, offset)))
+			return -EFAULT;
+		pos = off;
+		ret = do_sendfile(out_fd, in_fd, &pos, count, MAX_NON_LFS);
+		if (unlikely(put_user(pos, offset)))
+			return -EFAULT;
+		return ret;
+	}
+
+	return do_sendfile(out_fd, in_fd, NULL, count, 0);
+}
+
+COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
+		compat_loff_t __user *, offset, compat_size_t, count)
+{
+	loff_t pos;
+	ssize_t ret;
+
+	if (offset) {
+		if (unlikely(copy_from_user(&pos, offset, sizeof(loff_t))))
+			return -EFAULT;
+		ret = do_sendfile(out_fd, in_fd, &pos, count, 0);
+		if (unlikely(put_user(pos, offset)))
+			return -EFAULT;
+		return ret;
+	}
+
+	return do_sendfile(out_fd, in_fd, NULL, count, 0);
+}
+#endif
+

-- 
2.1.0

Many embedded systems will not need the splice-family syscalls (splice,
vmsplice, tee and sendfile). Omitting them saves space.  This adds a new EXPERT
config option CONFIG_SYSCALL_SPLICE (default y) to support compiling them out.

The goal is to completely compile out fs/splice along with the syscalls. To
achieve this, the remaining patch-set will deal with fs/splice exports. As far
as possible, the impact on other device drivers will be minimized so as to
reduce the overal maintenance burden of CONFIG_SYSCALL_SPLICE.

The use of exported functions will be solved by transparently mocking them out
with static inlines. Uses of the exported pipe_buf_operations struct however
require direct modification in fs/fuse and net/core. The next two patches will
deal with this.

The last change required before fs/splice can be comipled out is making fs/nfsd
aware of the lacking splice support in file-systems when CONFIG_SYSCALL_SPLICE
is undefined.

The bloat benefit of this patch given a tinyconfig is:

add/remove: 0/16 grow/shrink: 2/5 up/down: 114/-3693 (-3579)
function                                     old     new   delta
splice_direct_to_actor                       348     416     +68
splice_to_pipe                               371     417     +46
splice_from_pipe_next                        107     106      -1
fdput                                         11       -     -11
signal_pending                                39      26     -13
fdget                                         56      42     -14
user_page_pipe_buf_ops                        20       -     -20
user_page_pipe_buf_steal                      25       -     -25
file_end_write                                58      29     -29
file_start_write                              68      34     -34
pipe_to_user                                  43       -     -43
wakeup_pipe_readers                           54       -     -54
do_splice_to                                  87       -     -87
ipipe_prep.part                               92       -     -92
opipe_prep.part                              119       -    -119
sys_sendfile                                 122       -    -122
sys_sendfile64                               126       -    -126
sys_vmsplice                                 137       -    -137
vmsplice_to_user                             205       -    -205
sys_tee                                      491       -    -491
do_sendfile                                  492       -    -492
vmsplice_to_pipe                             558       -    -558
sys_splice                                  1020       -   -1020

Signed-off-by: Pieter Smith <redacted>
---
 fs/splice.c     |  2 ++
 init/Kconfig    | 10 ++++++++++
 kernel/sys_ni.c |  8 ++++++++
 3 files changed, 20 insertions(+)

diff --git a/fs/splice.c b/fs/splice.c
index 44b201b..7c4c695 100644
--- a/fs/splice.c
+++ b/fs/splice.c

@@ -1316,6 +1316,7 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
 	return ret;
 }
 
+#ifdef CONFIG_SYSCALL_SPLICE
 static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
 			       struct pipe_inode_info *opipe,
 			       size_t len, unsigned int flags);

@@ -2200,4 +2201,5 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
 	return do_sendfile(out_fd, in_fd, NULL, count, 0);
 }
 #endif
+#endif
 

diff --git a/init/Kconfig b/init/Kconfig
index d811d5f..dec9819 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -1571,6 +1571,16 @@ config NTP
 	  system clock to an NTP server, you can disable this option to save
 	  space.
 
+config SYSCALL_SPLICE
+	bool "Enable splice/vmsplice/tee/sendfile syscalls" if EXPERT
+	default y
+	help
+	  This option enables the splice, vmsplice, tee and sendfile syscalls. These
+	  are used by applications to: move data between buffers and arbitrary file
+	  descriptors; "copy" data between buffers; or copy data from userspace into
+	  buffers. If building an embedded system where no applications use these
+	  syscalls, you can disable this option to save space.
+
 config PCI_QUIRKS
 	default y
 	bool "Enable PCI quirk workarounds" if EXPERT

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d2f5b00..25d5551 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c

@@ -170,6 +170,14 @@ cond_syscall(sys_fstat);
 cond_syscall(sys_stat);
 cond_syscall(sys_uname);
 cond_syscall(sys_olduname);
+cond_syscall(sys_vmsplice);
+cond_syscall(sys_splice);
+cond_syscall(sys_tee);
+cond_syscall(sys_sendfile);
+cond_syscall(sys_sendfile64);
+cond_syscall(compat_sys_vmsplice);
+cond_syscall(compat_sys_sendfile);
+cond_syscall(compat_sys_sendfile64);
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read);

-- 
2.1.0

Entirely compile out splice translation unit when the system is configured
without splice family of syscalls (i.e. CONFIG_SYSCALL_SPLICE is undefined).

Exported fs/splice functions are transparently mocked out with static inlines.
Because userspace support for splice has already been removed by this
patch-set, the exported functions cannot be called anyway. Mocking them out
prevents a maintenance burden on file system drivers.

The bloat score resulting from this patch given a tinyconfig is:
add/remove: 0/25 grow/shrink: 0/5 up/down: 0/-4845 (-4845)
function                                     old     new   delta
pipe_to_null                                   4       -      -4
generic_pipe_buf_nosteal                       6       -      -6
spd_release_page                              10       -     -10
PageUptodate                                  22      11     -11
lock_page                                     36      24     -12
page_cache_pipe_buf_release                   16       -     -16
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
splice_shrink_spd                             27       -     -27
direct_splice_actor                           47       -     -47
default_file_splice_write                     49       -     -49
wakeup_pipe_writers                           54       -     -54
write_pipe_buf                                71       -     -71
page_cache_pipe_buf_confirm                   80       -     -80
splice_grow_spd                               87       -     -87
splice_from_pipe                              93       -     -93
splice_from_pipe_next                        106       -    -106
pipe_to_sendpage                             109       -    -109
page_cache_pipe_buf_steal                    114       -    -114
generic_file_splice_read                     131       8    -123
do_splice_direct                             148       -    -148
__splice_from_pipe                           246       -    -246
splice_direct_to_actor                       416       -    -416
splice_to_pipe                               417       -    -417
default_file_splice_read                     688       -    -688
iter_file_splice_write                       702       4    -698
__generic_file_splice_read                  1109       -   -1109

The bloat score for the entire CONFIG_SYSCALL_SPLICE patch-set is:
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

Signed-off-by: Pieter Smith <redacted>
---
 fs/Makefile            |  3 ++-
 fs/splice.c            |  2 --
 include/linux/fs.h     | 26 ++++++++++++++++++++++++++
 include/linux/splice.h | 42 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 70 insertions(+), 3 deletions(-)

diff --git a/fs/Makefile b/fs/Makefile
index fb7646e..9395622 100644
--- a/fs/Makefile
+++ b/fs/Makefile

@@ -10,7 +10,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		ioctl.o readdir.o select.o dcache.o inode.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
-		pnode.o splice.o sync.o utimes.o \
+		pnode.o sync.o utimes.o \
 		stack.o fs_struct.o statfs.o fs_pin.o
 
 ifeq ($(CONFIG_BLOCK),y)

@@ -22,6 +22,7 @@ endif
 obj-$(CONFIG_PROC_FS) += proc_namespace.o
 
 obj-$(CONFIG_FSNOTIFY)		+= notify/
+obj-$(CONFIG_SYSCALL_SPLICE)	+= splice.o
 obj-$(CONFIG_EPOLL)		+= eventpoll.o
 obj-$(CONFIG_ANON_INODES)	+= anon_inodes.o
 obj-$(CONFIG_SIGNALFD)		+= signalfd.o

diff --git a/fs/splice.c b/fs/splice.c
index 7c4c695..44b201b 100644
--- a/fs/splice.c
+++ b/fs/splice.c

@@ -1316,7 +1316,6 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
 	return ret;
 }
 
-#ifdef CONFIG_SYSCALL_SPLICE
 static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
 			       struct pipe_inode_info *opipe,
 			       size_t len, unsigned int flags);

@@ -2201,5 +2200,4 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
 	return do_sendfile(out_fd, in_fd, NULL, count, 0);
 }
 #endif
-#endif
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
index a957d43..138107e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h

@@ -2444,6 +2444,7 @@ extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end,
 extern void block_sync_page(struct page *page);
 
 /* fs/splice.c */
+#ifdef CONFIG_SYSCALL_SPLICE
 extern ssize_t generic_file_splice_read(struct file *, loff_t *,
 		struct pipe_inode_info *, size_t, unsigned int);
 extern ssize_t default_file_splice_read(struct file *, loff_t *,

@@ -2452,6 +2453,31 @@ extern ssize_t iter_file_splice_write(struct pipe_inode_info *,
 		struct file *, loff_t *, size_t, unsigned int);
 extern ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe,
 		struct file *out, loff_t *, size_t len, unsigned int flags);
+#else
+static inline ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
+		struct pipe_inode_info *pipe, size_t len, unsigned int flags)
+{
+	return -EPERM;
+}
+
+static inline ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
+		struct pipe_inode_info *pipe, size_t len, unsigned int flags)
+{
+	return -EPERM;
+}
+
+static inline ssize_t iter_file_splice_write(struct pipe_inode_info *pipe,
+		struct file *out, loff_t *ppos, size_t len, unsigned int flags)
+{
+	return -EPERM;
+}
+
+static inline ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe,
+		struct file *out, loff_t *ppos, size_t len, unsigned int flags)
+{
+	return -EPERM;
+}
+#endif
 
 extern void
 file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);

diff --git a/include/linux/splice.h b/include/linux/splice.h
index da2751d..34570d8 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h

@@ -65,6 +65,7 @@ typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
 typedef int (splice_direct_actor)(struct pipe_inode_info *,
 				  struct splice_desc *);
 
+#ifdef CONFIG_SYSCALL_SPLICE
 extern ssize_t splice_from_pipe(struct pipe_inode_info *, struct file *,
 				loff_t *, size_t, unsigned int,
 				splice_actor *);

@@ -74,13 +75,54 @@ extern ssize_t splice_to_pipe(struct pipe_inode_info *,
 			      struct splice_pipe_desc *);
 extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
 				      splice_direct_actor *);
+#else
+static inline ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
+			 loff_t *ppos, size_t len, unsigned int flags,
+			 splice_actor *actor)
+{
+	return -EPERM;
+}
+
+static inline ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
+			   splice_actor *actor)
+{
+	return -EPERM;
+}
+
+static inline ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
+		       struct splice_pipe_desc *spd)
+{
+	return -EPERM;
+}
+
+static inline ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
+			       splice_direct_actor *actor)
+{
+	return -EPERM;
+}
+#endif
 
 /*
  * for dynamic pipe sizing
  */
+#ifdef CONFIG_SYSCALL_SPLICE
 extern int splice_grow_spd(const struct pipe_inode_info *, struct splice_pipe_desc *);
 extern void splice_shrink_spd(struct splice_pipe_desc *);
 extern void spd_release_page(struct splice_pipe_desc *, unsigned int);
+#else
+static inline int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
+{
+	return -EPERM;
+}
+
+static inline void splice_shrink_spd(struct splice_pipe_desc *spd)
+{
+}
+
+static inline void spd_release_page(struct splice_pipe_desc *spd, unsigned int i)
+{
+}
+#endif
 
 extern const struct pipe_buf_operations page_cache_pipe_buf_ops;
 #endif

-- 
2.1.0

To implement splice support, fs/fuse 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 fs/fuse when
CONFIG_SYSCALL_SPLICE is undefined.

Signed-off-by: Pieter Smith <redacted>
---
 fs/fuse/dev.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ca88731..99f1ff4 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c

@@ -1291,6 +1291,7 @@ static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
 	return fuse_dev_do_read(fc, file, &cs, iov_length(iov, nr_segs));
 }
 
+#ifdef CONFIG_SYSCALL_SPLICE
 static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
 				    struct pipe_inode_info *pipe,
 				    size_t len, unsigned int flags)

@@ -1368,6 +1369,9 @@ out:
 	kfree(bufs);
 	return ret;
 }
+#else /* CONFIG_SYSCALL_SPLICE */
+#define fuse_dev_splice_read NULL
+#endif
 
 static int fuse_notify_poll(struct fuse_conn *fc, unsigned int size,
 			    struct fuse_copy_state *cs)

-- 
2.1.0

The goal of the larger patch set is to completely compile out fs/splice, and
as a result, splice support for all file-systems. This patch ensures that
fs/nfsd falls back to non-splice fs support when CONFIG_SYSCALL_SPLICE is
undefined.

Signed-off-by: Pieter Smith <redacted>
---
 net/sunrpc/svc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index ca8a795..6cacc37 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c

@@ -1084,7 +1084,7 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
 		goto err_short_len;
 
 	/* Will be turned off only in gss privacy case: */
-	rqstp->rq_splice_ok = true;
+	rqstp->rq_splice_ok = IS_ENABLED(CONFIG_SPLICE_SYSCALL);
 	/* Will be turned off only when NFSv4 Sessions are used */
 	rqstp->rq_usedeferral = true;
 	rqstp->rq_dropme = false;

-- 
2.1.0