When I first solved this problem I went for a fork() + setns() + clone() model.
This works fine but has unnecessary overhead for a couple of reasons:
- doing a full fork() including copying file descriptor table and virtual
memory
- using pipes to retrieve the pid of the second child (the actual container
process)
This can all be avoided by being a little smart in how we employ the clone()
syscall:
- using CLONE_VM will let us get rid of using pipes since we can simply write
to the handler because we share the memory with our parent
- using CLONE_VFORK will also let us get rid of using pipes since the execution
of the parent is suspended until the child returns
- using CLONE_VM will not cause virtual memory to be copied
- using CLONE_FILES will not cause the file descriptor table to be copied
Note that the intermediate clone() is used with CLONE_VM. Some glibc versions
used to reset the pid/tid to -1 when CLONE_VM was used without CLONE_THREAD.
But since the memory between parent and child is shared on CLONE_VM this would
invalidate the getpid() cache that glibc used to maintain and so getpid() in
the child would return the parent's pid. This is all fixed in newer glibc
versions where the getpid() cache is removed and the pid/tid is not reset
anymore. However, if for whatever reason you - dear commiter - somehow need to
get the pid of the dummy intermediate process for do_share_ns() you need to
call syscall(__NR_getpid) directly. The next lxc_clone() call does not employ
CLONE_VM and will be fine.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This fixes a bug introduced by:
commit 94f0035bf6
Author: Christian Brauner <christian.brauner@ubuntu.com>
Date: Thu Dec 7 15:07:26 2017 +0100
coverity: #1425924
remove logically dead condition
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Coverity's bug analysis is correct but my fix wasn't.
This commit fixes a bunch of other bugs I just spotted as well.
This unblocks #2009.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
The same message exists in lxclock.c and cgmanager.c, so print the
filename along with the message.
Before this patch:
lxc-destroy -n u1
pthread_mutex_unlock returned:1 Operation not permitted
After this patch:
xc-destroy -n u1
lxclock.c: pthread_mutex_unlock returned:1 Operation not permitted
Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Avoid NULL-pointer dereference. Apparently monitor.{c,h} calls
lxc_check_inherited() with NULL passed for the config. This isn't really a big
issue since monitor.{c,h} is effectively dead for all liblxc versions that have
the state client patch. Also, the patch that introduces the relevant lines into
lxc_check_inherited() is only in master and yet unreleased.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
lxc_init.c should not depend on tools/arguments.{c,h}, thus it needs its own custom argument parser
Signed-off-by: RicardoSanchezA <ricardo.sanchez@utexas.edu>
It doesn't make sense to error out when an app container doesn't pass explicit
arguments through c->start{l}(). This is especially true since we implemented
lxc.execute.cmd. However, even before we could have always relied on
lxc.init.cmd and errored out after that.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
