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

Josh Triplett
2014-11-22T21:51:07Z

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
>