[systemd-devel] [PATCH 1/2] nspawn: --populate to run static binaries on empty target directory

[Lennart Poettering]

On Sat, 30.11.13 10:20, Shawn Landden (shawn at churchofgit.com) wrote:

> nspawn has been called "chroot on steroids".
> 
> Continue that tradition by supporting target directories that
> are not root directories.
> 
> This patch handles the simple case: a static binary.

Hmm, I am not sure how I feel about this. This appears a bit too
specific for me, and given the requirement for static binaries this is
also so limited.

I wonder if we can find a different way to support this, without adding
high-level switches to nspawn itself.

For example, couldn't extending "--bind=" a bit to also support bind
mounting files (in contrast to just directories the way it currently
does) already gets us 90% of the way? And then do the rest 10% by adding
an example how to use this to bind mount static binaries from the host
into the container to the example in the man page? Allowing bind
mounting of files has been on the TODO list for a while anyway...

Something like:

# systemd-nspawn -D /srv/mycontainer --bind=/usr/bin/populate-container:/tmp/populate-container /tmp/populate-container

This of course wouldn't check if the file executed is staticall linked,
but the user should quickly get an error about missing .sos if it isn't?

>          assert_se(sigemptyset(&mask) == 0);
> @@ -1164,7 +1195,7 @@ int main(int argc, char *argv[]) {
>                          gid_t gid = (gid_t) -1;
>                          unsigned n_env = 2;
>                          const char *envp[] = {
> -                                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
> +                                DEFAULT_PATH_SPLIT_USR,

This bit looks like like something we really should do though. Could you
isolate this out and resubmit, please?

> +#define DEFAULT_PATH_SPLIT_USR "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
> +
>  #ifdef HAVE_SPLIT_USR
> -#  define DEFAULT_PATH "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
> +#  define DEFAULT_PATH DEFAULT_PATH_SPLIT_USR
>  #else
>  #  define DEFAULT_PATH "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin"
>  #endif
> @@ -51,6 +53,7 @@ int path_is_mount_point(const char *path, bool allow_symlink);
>  int path_is_read_only_fs(const char *path);
>  int path_is_os_tree(const char *path);

And this too, of course...

Lennart

-- 
Lennart Poettering, Red Hat