namespace: chase symlinks for mounts to set up in userspace

This adds logic to chase symlinks for all mount points that shall be created in
a namespace environment in userspace, instead of leaving this to the kernel.
This has the advantage that we can correctly handle absolute symlinks that
shall be taken relative to a specific root directory. Moreover, we can properly
handle mounts created on symlinked files or directories as we can merge their
mounts as necessary.

(This also drops the "done" flag in the namespace logic, which was never
actually working, but was supposed to permit a partial rollback of the
namespace logic, which however is only mildly useful as it wasn't clear in
which case it would or would not be able to roll back.)

Fixes: #3867

1 files changed, 2 insertions, 0 deletions

diff --git a/src/basic/fs-util.h b/src/basic/fs-util.h
index 2c3b9a1c74..31df47cf1e 100644
--- a/src/basic/fs-util.h
+++ b/src/basic/fs-util.h
@@ -77,3 +77,5 @@ union inotify_event_buffer {
 };
 
 int inotify_add_watch_fd(int fd, int what, uint32_t mask);
+
+int chase_symlinks(const char *path, const char *_root, char **ret);