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virt: detect cgroups namespaces

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detect_container() is now able to detect if we're running in a cgroup namespace.
This commit is contained in:
Sergey Bugaev 2020-12-20 14:43:01 +03:00
parent a4a9a6f7c6
commit 0e13779d37
1 changed files with 75 additions and 0 deletions
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75
src/basic/virt.c
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@ -9,6 +9,7 @@
#include <unistd.h>
#include "alloc-util.h"
#include "cgroup-util.h"
#include "dirent-util.h"
#include "env-util.h"
#include "fd-util.h"
@ -453,6 +454,72 @@ static const char *const container_table[_VIRTUALIZATION_MAX] = {
DEFINE_PRIVATE_STRING_TABLE_LOOKUP_FROM_STRING(container, int);
static int running_in_cgroupns(void) {
int r;
if (!cg_ns_supported())
return false;
r = cg_all_unified();
if (r < 0)
return r;
if (r) {
/* cgroup v2 */
r = access("/sys/fs/cgroup/cgroup.events", F_OK);
if (r < 0) {
if (errno != ENOENT)
return -errno;
/* All kernel versions have cgroup.events in nested cgroups. */
return false;
}
/* There's no cgroup.type in the root cgroup, and future kernel versions
* are unlikely to add it since cgroup.type is something that makes no sense
* whatsoever in the root cgroup. */
r = access("/sys/fs/cgroup/cgroup.type", F_OK);
if (r == 0)
return true;
if (r < 0 && errno != ENOENT)
return -errno;
/* On older kernel versions, there's no cgroup.type */
r = access("/sys/kernel/cgroup/features", F_OK);
if (r < 0) {
if (errno != ENOENT)
return -errno;
/* This is an old kernel that we know for sure has cgroup.events
* only in nested cgroups. */
return true;
}
/* This is a recent kernel, and cgroup.type doesn't exist, so we must be
* in the root cgroup. */
return false;
} else {
/* cgroup v1 */
/* If systemd controller is not mounted, do not even bother. */
r = access("/sys/fs/cgroup/systemd", F_OK);
if (r < 0) {
if (errno != ENOENT)
return -errno;
return false;
}
/* release_agent only exists in the root cgroup. */
r = access("/sys/fs/cgroup/systemd/release_agent", F_OK);
if (r < 0) {
if (errno != ENOENT)
return -errno;
return true;
}
return false;
}
}
static int detect_container_files(void) {
unsigned i;
@ -595,6 +662,14 @@ check_files:
if (r)
goto finish;
r = running_in_cgroupns();
if (r > 0) {
r = VIRTUALIZATION_CONTAINER_OTHER;
goto finish;
}
if (r < 0)
log_debug_errno(r, "Failed to detect cgroup namespace: %m");
/* If none of that worked, give up, assume no container manager. */
r = VIRTUALIZATION_NONE;
goto finish;