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

Pieter Smith
2014-12-04T17:51:48Z

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