monitord: close mainloop on exit if we opened it

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

log: drop all timezone conversion functions 

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

This allows us to generate nice timestamps in a thread-safe manner without
relying on locale touching functions from any libc.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Converts a unix time Epoch given by a struct timespec to a UTC string useable
in our logging functions. Maybe expanded to allow for more generic formatting.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Our log functions need to make extra sure that they are thread-safe. We had
some problems with that before. This especially involves time-conversion
functions. I don't want to find any localtime() or gmtime() functions or
relatives in here. Not even localtime_r() or gmtime_r() or relatives. They all
fiddle with global variables and locking in various libcs. They cause deadlocks
when liblxc is used multi-threaded and no matter how smart you think you are,
you __will__ cause trouble using them.
(As a short example how this can cause trouble: LXD uses forkstart to fork off
a new process that runs the container. At the same time the go runtime LXD
relies on does its own multi-threading thing which we can't control. The
fork()ing + threading then seems to mess with the locking states in these time
functions causing deadlocks.)
The current solution is to be good old unix people and use the Epoch as our
reference point and simply use the seconds and nanoseconds that have past since
then. This relies on clock_gettime() which is explicitly marked MT-Safe with no
restrictions! This way, anyone who is really strongly invested in getting the
actual time the log entry was created, can just convert it for themselves. Our
logging is mostly done for debugging purposes so don't try to make it pretty.
Pretty might cost you thread-safety.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

This macro can be used to set or allocate a string buffer that can hold any
64bit representable number.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

lxccontainer: log failure to send sig to init pid

conf: remove thread-unsafe strsignal + improve log

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

lxc_monitord: make lxc-monitord async signal safe

The thread-unsafe functions strsignal() is called in run_buffer() which in turn
is called in run_buffer_argv() which is responsible for running __all__ lxc
hooks. This is pretty dangerous for multi-threaded users like LXD.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Before lxc_monitord called lxc_monitord_cleanup() from a signal handler.  This
function calls a bunch of async signal unsafe functions and basically begs for
deadlocks. This commit switches lxc-monitord to using sigsetjmp() and
siglongjmp() in the signal handler to jump to a cleanup label that call
lxc_monitord_cleanup(). In this way, we avoid using async signal unsafe
functions.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

lxc_monitord: improve log + set log level to DEBUG

Setting loglevel to DEBUG will allow us to retrieve more useful information in
case something goes wrong. The total size of the log will not increase
significantly.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

commands: improve logging

monitor: add more logging

configure: remove -Werror=vla

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

Execing lxc-monitord is quite a crucial step so let's be very obsessive about
logging possible errors to guide us in debugging.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

lvm: supress warnings about leaked files

Because we include a header that uses a vla (/me scoffs at header).
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Closes #1283
Signed-off-by: Serge Hallyn <serge@hallyn.com>

cleanup monitor + improve log

conf, criu: add make_anonymous_mount_file()

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

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

tree-wide: remove any variable length arrays

Before we used tmpfile() to write out mount entries for the container. This
requires a writeable /tmp file system which can be a problem for systems where
this filesystem is not present. This commit switches from tmpfile() to using
the memfd_create() syscall. It allows us to create an anonymous tmpfs file (And
is somewhat similar to mmap().) which is automatically deleted as soon as any
references to it are dropped. In case we detect that syscall is not
implemented, we fallback to using tmpfile().
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>

They are pointless and marked optional since C11.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

log: fix race

There pointless and marked as optional since C11.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Sample log output:

    lxc 20161125201943.819 INFO     lxc_start - start.c:lxc_check_inherited:243 - Closed inherited fd: 54.
--> lxc N/A                INFO     lxc_monitor - monitor.c:lxc_monitor_sock_name:178 - using monitor sock name lxc/ad055575fe28ddd5//var/lib/lxc
    lxc 20161125201943.958 DEBUG    lxc_commands - commands.c:lxc_cmd_handler:893 - peer has disconnected
--> lxc N/A                DEBUG    lxc_commands - commands.c:lxc_cmd_get_state:579 - 'lxc-test-concurrent-0' is in 'RUNNING' state
    lxc 20161125201943.960 DEBUG    lxc_commands - commands.c:lxc_cmd_handler:893 - peer has disconnected
    lxc 20161125201944.009 INFO     lxc_start - start.c:lxc_check_inherited:243 - Closed inherited fd: 3.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

localtime_r() can lead to deadlocks because it calls __tzset() and
__tzconvert() internally. The deadlock stems from an interaction between these
functions and the functions in monitor.c and commands.{c,h}. The latter
functions will write to the log independent of the container thread that is
currently running. Since the monitor fork()ed it seems to duplicate the mutex
states of the time functions mentioned above causing the deadlock.
As a short termm fix, I suggest to simply disable receiving the time when
monitor.c or command.{c,h} functions are called. This should be ok, since the
[lxc monitor] will only emit a few messages and thread-safety is currently more
important than beautiful logs. The rest of the log stays the same as it was
before.

Here is an example output from logs where I printed the pid and tid of the
process that is currently writing to the log:

            lxc 20161125170200.619 INFO     lxc_start:   18695-18695: - start.c:lxc_check_inherited:243 - Closed inherited fd: 23.
            lxc 20161125170200.640 DEBUG    lxc_start:   18677-18677: - start.c:__lxc_start:1334 - Not dropping CAP_SYS_BOOT or watching utmp.
            lxc 20161125170200.640 INFO     lxc_cgroup:  18677-18677: - cgroups/cgroup.c:cgroup_init:68 - cgroup driver cgroupfs-ng initing for lxc-test-concurrent-0

----------> lxc 20150427012246.000 INFO     lxc_monitor: 13017-18622: - monitor.c:lxc_monitor_sock_name:178 - using monitor sock name lxc/ad055575fe28ddd5//var/lib/lxc

            lxc 20161125170200.662 DEBUG    lxc_cgfsng:  18677-18677: - cgroups/cgfsng.c:filter_and_set_cpus:478 - No isolated cpus detected.
            lxc 20161125170200.662 DEBUG    lxc_cgfsng:  18677-18677: - cgroups/cgfsng.c:handle_cpuset_hierarchy:648 - "cgroup.clone_children" was already set to "1".
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

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

cleanup attach

log: use thread-safe localtime_r()