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core: keep supporting cgroup hybrid layout from v232 for live upgrades 

v232's cgroup hybrid mode mounted v2 on /sys/fs/cgroup/systemd, which
unfortunately broke other tools which expect v1 there.  From v233 on, hybrid
mode instead mounts and uses v2 on /sys/fs/cgroup/unified and keeps
/sys/fs/cgroup/systemd on v1 for compatibility with external tools.  However,
to keep systemd live upgrades working, v233+ should be able to recognize v232
layout and keep using it.

This patch adds v232 hybrid mode support.  If v232 layout is detected,
cg_unified(SYSTEMD_CGRouP_CONTROLLER) keeps returning %true but
cg_hybrid_unified() returns %false.  This keeps process management on cgroup v2
but turns off the parallel layout.
This commit is contained in:
Tejun Heo 2016-11-23 12:27:32 -05:00 committed by Zbigniew Jędrzejewski-Szmek
parent 2977724b09
commit f08e928720
1 changed files with 22 additions and 3 deletions
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25
src/basic/cgroup-util.c
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@ -2283,6 +2283,20 @@ int cg_kernel_controllers(Set *controllers) {
static thread_local CGroupUnified unified_cache = CGROUP_UNIFIED_UNKNOWN;
/* The hybrid mode was initially implemented in v232 and simply mounted
* cgroup v2 on /sys/fs/cgroup/systemd. This unfortunately broke other
* tools (such as docker) which expected the v1 "name=systemd" hierarchy
* on /sys/fs/cgroup/systemd. From v233 and on, the hybrid mode mountnbs
* v2 on /sys/fs/cgroup/unified and maintains "name=systemd" hierarchy
* on /sys/fs/cgroup/systemd for compatibility with other tools.
*
* To keep live upgrade working, we detect and support v232 layout. When
* v232 layout is detected, to keep cgroup v2 process management but
* disable the compat dual layout, we return %true on
* cg_unified(SYSTEMD_CGROUP_CONTROLLER) and %false on cg_hybrid_unified().
*/
static thread_local bool unified_systemd_v232;
static int cg_update_unified(void) {
struct statfs fs;
@ -2302,9 +2316,14 @@ static int cg_update_unified(void) {
unified_cache = CGROUP_UNIFIED_ALL;
else if (F_TYPE_EQUAL(fs.f_type, TMPFS_MAGIC)) {
if (statfs("/sys/fs/cgroup/unified/", &fs) == 0 &&
F_TYPE_EQUAL(fs.f_type, CGROUP2_SUPER_MAGIC))
F_TYPE_EQUAL(fs.f_type, CGROUP2_SUPER_MAGIC)) {
unified_cache = CGROUP_UNIFIED_SYSTEMD;
else {
unified_systemd_v232 = false;
} else if (statfs("/sys/fs/cgroup/systemd/", &fs) == 0 &&
F_TYPE_EQUAL(fs.f_type, CGROUP2_SUPER_MAGIC)) {
unified_cache = CGROUP_UNIFIED_SYSTEMD;
unified_systemd_v232 = true;
} else {
if (statfs("/sys/fs/cgroup/systemd/", &fs) < 0)
return -errno;
if (!F_TYPE_EQUAL(fs.f_type, CGROUP_SUPER_MAGIC))
@ -2336,7 +2355,7 @@ bool cg_hybrid_unified(void) {
assert(cg_update_unified() >= 0);
return unified_cache == CGROUP_UNIFIED_SYSTEMD;
return unified_cache == CGROUP_UNIFIED_SYSTEMD && !unified_systemd_v232;
}
int cg_unified_flush(void) {