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Commit 2e13ba54 authored by Iago López Galeiras's avatar Iago López Galeiras Committed by Linus Torvalds
Browse files

fs, proc: introduce CONFIG_PROC_CHILDREN 



Commit 81841161 ("fs, proc: introduce /proc/<pid>/task/<tid>/children
entry") introduced the children entry for checkpoint restore and the
file is only available on kernels configured with CONFIG_EXPERT and
CONFIG_CHECKPOINT_RESTORE.

This is available in most distributions (Fedora, Debian, Ubuntu, CoreOS)
because they usually enable CONFIG_EXPERT and CONFIG_CHECKPOINT_RESTORE.
But Arch does not enable CONFIG_EXPERT or CONFIG_CHECKPOINT_RESTORE.

However, the children proc file is useful outside of checkpoint restore.
I would like to use it in rkt.  The rkt process exec() another program
it does not control, and that other program will fork()+exec() a child
process.  I would like to find the pid of the child process from an
external tool without iterating in /proc over all processes to find
which one has a parent pid equal to rkt.

This commit introduces CONFIG_PROC_CHILDREN and makes
CONFIG_CHECKPOINT_RESTORE select it.  This allows enabling
/proc/<pid>/task/<tid>/children without needing to enable
CONFIG_CHECKPOINT_RESTORE and CONFIG_EXPERT.

Alban tested that /proc/<pid>/task/<tid>/children is present when the
kernel is configured with CONFIG_PROC_CHILDREN=y but without
CONFIG_CHECKPOINT_RESTORE

Signed-off-by: default avatarIago López Galeiras <iago@endocode.com>
Tested-by: default avatarAlban Crequy <alban@endocode.com>
Reviewed-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Djalal Harouni <djalal@endocode.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c2c0bb44

fs/proc/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -71,3 +71,7 @@ config PROC_PAGE_MONITOR 
	  /proc/pid/smaps, /proc/pid/clear_refs, /proc/pid/pagemap,

	  /proc/kpagecount, and /proc/kpageflags. Disabling these

          interfaces will reduce the size of the kernel by approximately 4kb.



config PROC_CHILDREN

	bool "Include /proc/<pid>/task/<tid>/children file"

	default n

fs/proc/array.c

+2 −2
Original line number Diff line number Diff line
@@ -577,7 +577,7 @@ int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns, 
	return 0;

}



#ifdef CONFIG_CHECKPOINT_RESTORE

#ifdef CONFIG_PROC_CHILDREN

static struct pid *

get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)

{
@@ -700,4 +700,4 @@ const struct file_operations proc_tid_children_operations = { 
	.llseek  = seq_lseek,

	.release = children_seq_release,

};

#endif /* CONFIG_CHECKPOINT_RESTORE */
 
#endif /* CONFIG_PROC_CHILDREN */

fs/proc/base.c

+1 −1
Original line number Diff line number Diff line
@@ -3109,7 +3109,7 @@ static const struct pid_entry tid_base_stuff[] = { 
	ONE("stat",      S_IRUGO, proc_tid_stat),

	ONE("statm",     S_IRUGO, proc_pid_statm),

	REG("maps",      S_IRUGO, proc_tid_maps_operations),

#ifdef CONFIG_CHECKPOINT_RESTORE

#ifdef CONFIG_PROC_CHILDREN

	REG("children",  S_IRUGO, proc_tid_children_operations),

#endif

#ifdef CONFIG_NUMA

init/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -1131,6 +1131,7 @@ endif # CGROUPS 


config CHECKPOINT_RESTORE

	bool "Checkpoint/restore support" if EXPERT

	select PROC_CHILDREN

	default n

	help

	  Enables additional kernel features in a sake of checkpoint/restore.