[PATCH 1/6] fs: move sendfile syscall into fs/splice

[PATCH 1/6] fs: move sendfile syscall into fs/splice

[Pieter Smith]

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 <pieter@boesman.nl>
---
 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
+
-- 
1.9.1

[PATCH 2/6] fs: moved kernel_write to fs/read_write

[Pieter Smith]

kernel_write shares infrastructure with the read_write translation unit but not
with the splice translation unit. Grouping kernel_write with the read_write
translation unit is more logical. It also paves the way to compiling out the
splice group of syscalls for embedded systems that do not need them.

Signed-off-by: Pieter Smith <pieter@boesman.nl>
---
 fs/read_write.c | 16 ++++++++++++++++
 fs/splice.c     | 16 ----------------
 2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index d9451ba..f4c8d8b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1191,3 +1191,19 @@ COMPAT_SYSCALL_DEFINE5(pwritev, compat_ulong_t, fd,
 }
 #endif
 
+ssize_t kernel_write(struct file *file, const char *buf, size_t count,
+			    loff_t pos)
+{
+	mm_segment_t old_fs;
+	ssize_t res;
+
+	old_fs = get_fs();
+	set_fs(get_ds());
+	/* The cast to a user pointer is valid due to the set_fs() */
+	res = vfs_write(file, (__force const char __user *)buf, count, &pos);
+	set_fs(old_fs);
+
+	return res;
+}
+EXPORT_SYMBOL(kernel_write);
+
diff --git a/fs/splice.c b/fs/splice.c
index c1a2861..44b201b 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -583,22 +583,6 @@ static ssize_t kernel_readv(struct file *file, const struct iovec *vec,
 	return res;
 }
 
-ssize_t kernel_write(struct file *file, const char *buf, size_t count,
-			    loff_t pos)
-{
-	mm_segment_t old_fs;
-	ssize_t res;
-
-	old_fs = get_fs();
-	set_fs(get_ds());
-	/* The cast to a user pointer is valid due to the set_fs() */
-	res = vfs_write(file, (__force const char __user *)buf, count, &pos);
-	set_fs(old_fs);
-
-	return res;
-}
-EXPORT_SYMBOL(kernel_write);
-
 ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
 				 struct pipe_inode_info *pipe, size_t len,
 				 unsigned int flags)
-- 
1.9.1

[PATCH 3/6] fs/splice: support compiling out splice-family syscalls

[Pieter Smith]

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.

This patch removes almost all callers of .splice_read() and .splice_write()
in the file_operations struct. This paves the way to eventually compile out the
.splice_read and .splice_write members of the file_operations struct as well as
the remaining splice-related infrastructure.

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 <pieter@boesman.nl>
---
 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);
-- 
1.9.1

[PATCH 4/6] fs/fuse: support compiling out splice

[Pieter Smith]

Compile out splice support from fuse 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>
---
 fs/fuse/dev.c      | 4 ++--
 include/linux/fs.h | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ca88731..f8f92a4 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1291,7 +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));
 }
 
-static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
+static ssize_t __maybe_unused fuse_dev_splice_read(struct file *in, loff_t *ppos,
 				    struct pipe_inode_info *pipe,
 				    size_t len, unsigned int flags)
 {
@@ -2144,7 +2144,7 @@ const struct file_operations fuse_dev_operations = {
 	.llseek		= no_llseek,
 	.read		= do_sync_read,
 	.aio_read	= fuse_dev_read,
-	.splice_read	= fuse_dev_splice_read,
+	.splice_read	= __splice_p(fuse_dev_splice_read),
 	.write		= do_sync_write,
 	.aio_write	= fuse_dev_write,
 	.splice_write	= fuse_dev_splice_write,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a957d43..04c0975 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2443,6 +2443,12 @@ extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end,
 			int datasync);
 extern void block_sync_page(struct page *page);
 
+#ifdef CONFIG_SYSCALL_SPLICE
+#define __splice_p(x) x
+#else
+#define __splice_p(x) NULL
+#endif
+
 /* fs/splice.c */
 extern ssize_t generic_file_splice_read(struct file *, loff_t *,
 		struct pipe_inode_info *, size_t, unsigned int);
-- 
1.9.1

[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

[PATCH 6/6] fs/splice: full support for compiling out splice

[Pieter Smith]

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

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

Signed-off-by: Pieter Smith <pieter@boesman.nl>
---
 fs/Makefile            |  3 ++-
 fs/splice.c            |  2 --
 include/linux/fs.h     | 26 ++++++++++++++++++++++++++
 include/linux/splice.h | 43 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 71 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 04c0975..9b3054e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2449,6 +2449,7 @@ extern void block_sync_page(struct page *page);
 #define __splice_p(x) NULL
 #endif
 
+#ifdef CONFIG_SYSCALL_SPLICE
 /* fs/splice.c */
 extern ssize_t generic_file_splice_read(struct file *, loff_t *,
 		struct pipe_inode_info *, size_t, unsigned int);
@@ -2458,6 +2459,31 @@ 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..50ca77f 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 +75,55 @@ 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 /* #ifdef CONFIG_SYSCALL_SPLICE */
+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 /* #ifdef CONFIG_SYSCALL_SPLICE */
 
 /*
  * 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 /* #ifdef CONFIG_SYSCALL_SPLICE */
+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 /* #ifdef CONFIG_SYSCALL_SPLICE */
 
 extern const struct pipe_buf_operations page_cache_pipe_buf_ops;
+
 #endif
-- 
1.9.1

Re: [PATCH 4/6] fs/fuse: support compiling out splice

[Josh Triplett]

On Sat, Nov 22, 2014 at 09:59:59PM +0100, Pieter Smith wrote:
> Compile out splice support from fuse when the splice-family of syscalls is not
> supported by the system (i.e. CONFIG_SYSCALL_SPLICE is undefined).

This patch needs some additional explanation.  Could you explain in the
commit message why this particular splice_read function (and only the
splice_read function, not the splice_write function) needs compiling
out, when others do not?

- Josh Triplett

> Signed-off-by: Pieter Smith <pieter@boesman.nl>
> ---
>  fs/fuse/dev.c      | 4 ++--
>  include/linux/fs.h | 6 ++++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index ca88731..f8f92a4 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -1291,7 +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));
>  }
>  
> -static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
> +static ssize_t __maybe_unused fuse_dev_splice_read(struct file *in, loff_t *ppos,
>  				    struct pipe_inode_info *pipe,
>  				    size_t len, unsigned int flags)
>  {
> @@ -2144,7 +2144,7 @@ const struct file_operations fuse_dev_operations = {
>  	.llseek		= no_llseek,
>  	.read		= do_sync_read,
>  	.aio_read	= fuse_dev_read,
> -	.splice_read	= fuse_dev_splice_read,
> +	.splice_read	= __splice_p(fuse_dev_splice_read),
>  	.write		= do_sync_write,
>  	.aio_write	= fuse_dev_write,
>  	.splice_write	= fuse_dev_splice_write,
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index a957d43..04c0975 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2443,6 +2443,12 @@ extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end,
>  			int datasync);
>  extern void block_sync_page(struct page *page);
>  
> +#ifdef CONFIG_SYSCALL_SPLICE
> +#define __splice_p(x) x
> +#else
> +#define __splice_p(x) NULL
> +#endif
> +
>  /* fs/splice.c */
>  extern ssize_t generic_file_splice_read(struct file *, loff_t *,
>  		struct pipe_inode_info *, size_t, unsigned int);
> -- 
> 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 3/6] fs/splice: support compiling out splice-family syscalls

[Josh Triplett]

On Sat, Nov 22, 2014 at 09:59:58PM +0100, Pieter Smith wrote:
> 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.
> 
> This patch removes almost all callers of .splice_read() and .splice_write()
> in the file_operations struct. This paves the way to eventually compile out the
> .splice_read and .splice_write members of the file_operations struct as well as
> the remaining splice-related infrastructure.

This commit message doesn't reflect the new approach of leaving those
members in the structure.

The patch looks good otherwise.

- Josh Triplett

> 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 <pieter@boesman.nl>
> ---
>  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);
> -- 
> 1.9.1
> 

Re: [PATCH 6/6] fs/splice: full support for compiling out splice

[Josh Triplett]

On Sat, Nov 22, 2014 at 10:00:01PM +0100, Pieter Smith wrote:
> Entirely compile out splice translation unit when the system is configured
> without splice family of syscalls (i.e. CONFIG_SYSCALL_SPLICE is undefined).
> 
> add/remove: 0/25 grow/shrink: 0/5 up/down: 0/-4845 (-4845)

Very nice!

- Josh Triplett

> 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
> 
> Signed-off-by: Pieter Smith <pieter@boesman.nl>
> ---
>  fs/Makefile            |  3 ++-
>  fs/splice.c            |  2 --
>  include/linux/fs.h     | 26 ++++++++++++++++++++++++++
>  include/linux/splice.h | 43 +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 71 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 04c0975..9b3054e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2449,6 +2449,7 @@ extern void block_sync_page(struct page *page);
>  #define __splice_p(x) NULL
>  #endif
>  
> +#ifdef CONFIG_SYSCALL_SPLICE
>  /* fs/splice.c */
>  extern ssize_t generic_file_splice_read(struct file *, loff_t *,
>  		struct pipe_inode_info *, size_t, unsigned int);
> @@ -2458,6 +2459,31 @@ 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..50ca77f 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 +75,55 @@ 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 /* #ifdef CONFIG_SYSCALL_SPLICE */
> +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 /* #ifdef CONFIG_SYSCALL_SPLICE */
>  
>  /*
>   * 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 /* #ifdef CONFIG_SYSCALL_SPLICE */
> +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 /* #ifdef CONFIG_SYSCALL_SPLICE */
>  
>  extern const struct pipe_buf_operations page_cache_pipe_buf_ops;
> +
>  #endif
> -- 
> 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 4/6] fs/fuse: support compiling out splice

[Pieter Smith]

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 <pieter@boesman.nl>
---
 fs/fuse/dev.c      | 4 ++--
 include/linux/fs.h | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ca88731..f8f92a4 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1291,7 +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));
 }
 
-static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
+static ssize_t __maybe_unused fuse_dev_splice_read(struct file *in, loff_t *ppos,
 				    struct pipe_inode_info *pipe,
 				    size_t len, unsigned int flags)
 {
@@ -2144,7 +2144,7 @@ const struct file_operations fuse_dev_operations = {
 	.llseek		= no_llseek,
 	.read		= do_sync_read,
 	.aio_read	= fuse_dev_read,
-	.splice_read	= fuse_dev_splice_read,
+	.splice_read	= __splice_p(fuse_dev_splice_read),
 	.write		= do_sync_write,
 	.aio_write	= fuse_dev_write,
 	.splice_write	= fuse_dev_splice_write,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a957d43..04c0975 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2443,6 +2443,12 @@ extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end,
 			int datasync);
 extern void block_sync_page(struct page *page);
 
+#ifdef CONFIG_SYSCALL_SPLICE
+#define __splice_p(x) x
+#else
+#define __splice_p(x) NULL
+#endif
+
 /* fs/splice.c */
 extern ssize_t generic_file_splice_read(struct file *, loff_t *,
 		struct pipe_inode_info *, size_t, unsigned int);
-- 
2.1.0