[PATCH 00/10] tinification: Make memory-access char devices optional

From: Tom Zanussi
Date: Fri Jan 23 2015 - 13:37:39 EST

This patchset adds a top-level config option, CONFIG_DEVMEM_BASE, and
a series of dependent options below it which allow various devices
such as /dev/mem, /dev/null, /dev/zero, /dev/random, etc. to be
disabled. This allows embedded systems systems that don't need any or
all of those devices to save the kernel memory associated with those
devices.

It also adds a related option to disable the getrandom(2) syscall,
CONFIG_GETRANDOM_SYSCALL, which allows code shared between it and
/dev/*random to be compiled out as well.

Disabling of CONFIG_DEVMEM_BASE and its dependent options is only
available if CONFIG_EMBEDDED is enabled; normal systems will still
have everything enabled as usual.

bloat-o-meter shows a total 6k savings for a tinyconfig kernel with
all options disabled, and about 10k savings for the same thing but
using defconfig.

bloat-o-meter (based on tinyconfig):

add/remove: 0/55 grow/shrink: 1/3 up/down: 332/-6563 (-6231)
function old new delta
extract_entropy 114 446 +332
__print_once 13 12 -1
write_null 3 - -3
read_null 3 - -3
mix_pool_bytes 17 14 -3
aio_read_null 3 - -3
pipe_to_null 4 - -4
mem_class 4 - -4
write_full 6 - -6
devkmsg_release 15 - -15
random_fasync 16 - -16
mmap_zero 16 - -16
aio_write_null 18 - -18
open_port 19 - -19
random_read 20 - -20
splice_write_null 24 - -24
null_lseek 25 - -25
mmap_mem_ops 32 - -32
mem_devnode 35 - -35
mmap_kmem 37 - -37
random_write 42 - -42
xfer_secondary_pool 60 - -60
write_pool 82 - -82
random_poll 83 - -83
read_iter_zero 95 - -95
urandom_read 96 - -96
memory_open 96 - -96
devkmsg_poll 97 - -97
read_port 98 - -98
mmap_mem 103 - -103
devkmsg_open 112 - -112
write_port 116 - -116
zero_fops 120 - -120
urandom_fops 120 - -120
random_fops 120 - -120
port_fops 120 - -120
null_fops 120 - -120
memory_fops 120 - -120
mem_fops 120 - -120
kmsg_fops 120 - -120
kmem_fops 120 - -120
full_fops 120 - -120
memory_lseek 122 - -122
devkmsg_llseek 144 - -144
chr_dev_init 162 3 -159
read_mem 162 - -162
extract_buf 164 - -164
_random_read.part 173 - -173
account 181 - -181
write_mem 184 - -184
devlist 192 - -192
extract_entropy_user 197 - -197
devkmsg_write 209 - -209
sys_getrandom 211 - -211
zero_bdi 244 - -244
read_kmem 290 - -290
random_ioctl 319 - -319
write_kmem 349 - -349
devkmsg_read 699 - -699


The following changes since commit 5eb11d6b3f55eb4d28c51ea7f641c0e5e255a70f:

Merge tag 'sound-3.19-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound (2015-01-21 20:37:25 +1200)

are available in the git repository at:

git://git.yoctoproject.org/linux-yocto-contrib.git tzanussi/devmem-tinification-v1
http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-contrib/log/?h=tzanussi/devmem-tinification-v1

Tom Zanussi (10):
drivers/char: Support compiling out memory-access char devices
drivers/char: Support compiling out /dev/mem
drivers/char: Support compiling out /dev/port
drivers/char: Support compiling out /dev/null
drivers/char: Support compiling out /dev/zero
drivers/char: Support compiling out /dev/full
drivers/char: Support compiling out /dev/random
drivers/char: Support compiling out /dev/urandom
drivers/char: Support compiling out /dev/kmsg
drivers/char: Support compiling out the getrandom(2) syscall

arch/x86/Kconfig.debug | 1 +
drivers/char/Kconfig | 109 ++++++++++++++++++++++++++++++++++++++++++++++++-
drivers/char/mem.c | 83 +++++++++++++++++++++++++++----------
drivers/char/random.c | 24 ++++++++---
kernel/printk/printk.c | 2 +
kernel/sys_ni.c | 1 +
6 files changed, 192 insertions(+), 28 deletions(-)

--
1.9.3

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