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

Pieter Smith
2014-11-22T21:01:46Z

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