This commit introduces my concept of a network namespace aware
getifaddrs(), i.e. netns_getifaddrs(). This presupposes a kernel that
carries my IF{L}A_TARGET_NETNSID patches:

struct netns_ifaddrs {
        struct netns_ifaddrs *ifa_next;

        /* Can - but shouldn't be - NULL. */
        char *ifa_name;

        /* This field is not present struct ifaddrs. */
        int ifa_ifindex;

        unsigned ifa_flags;

        /* This field is not present struct ifaddrs. */
        int ifa_mtu;

        /* This field is not present struct ifaddrs. */
        int ifa_prefixlen;

        struct sockaddr *ifa_addr;
        struct sockaddr *ifa_netmask;
        union {
                struct sockaddr *ifu_broadaddr;
                struct sockaddr *ifu_dstaddr;
        } ifa_ifu;

        /* If you don't know what this is for don't touch it. */
        void *ifa_data;
};

which is a superset of struct ifaddrs. It contains additional
information such as the mtu, ifindex of the interface and the prefix
length of the address.
Note that the field ordering is different. So don't get any ideas of
using memcpy() to copy from an old struct ifaddrs into a struct
netns_ifaddrs.

int netns_getifaddrs(struct netns_ifaddrs **ifap, __s32 netns_id, bool *netnsid_aware)

takes a network namespace identifier as argument which identifies the
target network namespace.
If successfull, i.e. netns_getifaddrs() returns 0, callers should check
the bool *netnsid_aware return argument. If it is true then
RTM_GET{ADDR,LINK} requests are fully netnsid aware. If it is false then
they are not and the information returned in struct netns_ifaddrs does
*not* contain correct information about the target network namespace
identified by netnsid.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

compiler: compiler based hardening

compiler: __attribute__((noreturn)) on bionic

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

macro: add STRLITERALLEN() and STRARRAYLEN() 

cgfsng: copy parent's cpu settings for monitor too

Closes https://github.com/lxc/lxd/issues/5060.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

sizeof() implementation for string literals and string arrays that makes
it behave like strlen() for strings.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

autotools: fix check for -Wimplicit-fallthrough

conf: realpath() uses null as second parameter to prevent buffer overflow

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

cgroups: scoping for cgroup v2

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

brauner@wittgenstein|~
> sudo systemctl status lxc@c1
● lxc@c1.service - LXC Container: c1
   Loaded: loaded (/lib/systemd/system/lxc@.service; disabled; vendor preset: enabled)
   Active: active (running) since Tue 2018-09-11 10:42:22 CEST; 38s ago
     Docs: man:lxc-start
           man:lxc
  Process: 29855 ExecStart=/usr/bin/lxc-start -n c1 -p /run/lxc/c1.pid (code=exited, status=0/SUCCESS)
    Tasks: 18 (limit: 4915)
   Memory: 32.1M
   CGroup: /system.slice/system-lxc.slice/lxc@c1.service
           ├─lxc.monitor
           │ └─c1
           │   └─29870 [lxc monitor] /var/lib/lxc c1
           └─lxc.payload
             └─c1
               ├─init.scope
               │ └─29878 /sbin/init
               └─system.slice
                 ├─console-getty.service
                 │ └─30028 /sbin/agetty -o -p -- \u --noclear --keep-baud console 115200,38400,9600 linux
                 ├─cron.service
                 │ └─30019 /usr/sbin/cron -f
                 ├─dbus.service
                 │ └─30020 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
                 ├─networkd-dispatcher.service
                 │ └─30016 /usr/bin/python3 /usr/bin/networkd-dispatcher --run-startup-triggers
                 ├─rsyslog.service
                 │ └─30017 /usr/sbin/rsyslogd -n
                 ├─system-container\x2dgetty.slice
                 │ ├─container-getty@0.service
                 │ │ └─30027 /sbin/agetty -o -p -- \u --noclear --keep-baud pts/0 115200,38400,9600 vt220
                 │ ├─container-getty@1.service
                 │ │ └─30030 /sbin/agetty -o -p -- \u --noclear --keep-baud pts/1 115200,38400,9600 vt220
                 │ ├─container-getty@2.service
                 │ │ └─30026 /sbin/agetty -o -p -- \u --noclear --keep-baud pts/2 115200,38400,9600 vt220
                 │ └─container-getty@3.service
                 │   └─30029 /sbin/agetty -o -p -- \u --noclear --keep-baud pts/3 115200,38400,9600 vt220
                 ├─systemd-journald.service
                 │ └─29976 /lib/systemd/systemd-journald
                 ├─systemd-logind.service
                 │ └─30018 /lib/systemd/systemd-logind
                 ├─systemd-networkd.service
                 │ └─29996 /lib/systemd/systemd-networkd
                 ├─systemd-resolved.service
                 │ └─30014 /lib/systemd/systemd-resolved
                 └─systemd-udevd.service
                   └─29986 /lib/systemd/systemd-udevd
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

autotools: add -Wimplicit-fallthrough

api_extensions: introduce lxc_has_api_extension()

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

This is modeled after LXD's API extension checks. This allows API users
to query the given LXC instance whether a given API extension is
supported.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

cgfsng: mark ops with __cgfsng_ops__ attribute

confile: s/lxc.cgroup.keep/lxc.cgroup.relative/g

conf: remove extra MS_BIND with sysfs:mixed

Helps to easily tell the cgfsng ops functions from helpers.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>