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Subject[PATCH 0/5] A config option to compile out some namespaces code (v2)
Changes from v1:
* make the NAMESPACES_EXPERIMENTAL selectable even in !EMBEDDED case

There were some questions like "do I need this on my cellphone"
in reply to different namespaces patches. Indeed, the namespaces
are not useful for most of the embedded systems, but the code
creating and releasing them weights a lot.

So I propose to add a config option which will help embedded
people to reduce the vmlinux size. This option simply compiles
out the namespaces cloning and releasing code *only*, but keeps
all the other logic untouched (e.g. the notion of init_ns).

When someone tries to clone some namespace with their support
turned off, he will receive an EINVAL error.

This patchset can save more than 2KB from the vmlinux when
turning the config option "NAMESPACES" to "n":

$ scripts/bloat-o-meter vmlinux-no-ns vmlinux-with-ns
add/remove: 27/0 grow/shrink: 11/7 up/down: 2477/-340 (2137)
function old new delta
copy_pid_ns - 537 +537
copy_user_ns - 181 +181
copy_ipcs - 149 +149
zap_pid_ns_processes - 130 +130
copy_utsname - 120 +120
shm_exit_ns - 106 +106
sem_exit_ns - 106 +106
msg_exit_ns - 106 +106
freeary - 100 +100
release_uids - 95 +95
freeque - 92 +92
free_nsproxy 48 123 +75
create_new_namespaces 300 358 +58
free_pid_ns - 56 +56
pid_namespaces_init - 48 +48
__sem_init_ns - 45 +45
shm_init_ns - 42 +42
sem_init_ns - 42 +42
msg_init_ns - 42 +42
__shm_init_ns - 38 +38
__msg_init_ns - 31 +31
sysvipc_proc_release 5 35 +30
proc_kill_sb 5 35 +30
free_ipc_ns - 30 +30
do_shm_rmid - 29 +29
proc_set_super 13 38 +25
shm_release 18 39 +21
put_pid 75 95 +20
alloc_pid 687 706 +19
pid_caches_mutex - 16 +16
free_user_ns - 16 +16
sysvipc_proc_open 100 111 +11
do_shmat 778 787 +9
pid_caches_lh - 8 +8
free_uts_ns - 5 +5
pid_ns_cachep - 4 +4
__initcall_pid_namespaces_init6 - 4 +4
do_exit 1855 1856 +1
show_stat 1665 1661 -4
sys_shmctl 1934 1907 -27
msg_init 82 47 -35
shm_init 92 47 -45
sem_init 99 44 -55
sys_msgctl 1394 1311 -83
sys_semctl 2123 2032 -91

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
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