system/skeleton: move target of /etc/resolv.conf symlink
In commit ba70f94e629e (subversion makes it so we do not need a separate
tarball to store empty directories and symlinks for the target_skeleton.)
/etc/resolv.conf was made a symlink to ../tmp/resolv.conf. There was no
rationale behind this change, but back at the time (2006!), the only
location that Buildroot guaranteed to be writable was /tmp, and we
needed a writable location to create resolv.conf from a DHCP reply for
example, so the change made sense.
Commits 2f67d9e2fe7b (preparation for BR2_PACKAGE_BUSYBOX_SKELETON), in
2007, then d9119c0bc55d (move default skeleton to fs/ and drop busybox
skeleton), in 2010, and finally 6c3e3ad41977 (New top-level directory:
system), in 2012, propagated that /etc/resolv.conf without any change in
the target of the symlink.
However, since commit d380dde1d287 (skeleton: make /run a proper
directory/filesystem), in 2015, a tmpfs has been mounted on /run, so it
is now guaranteed to be writable as well for SYS-V-based systems. That
has also been the case for openrc since commit a840e485d174
(package/skeleton-init-openrc: new package), in 2019. This has also
always been the case for systemd as well.
resolv.conf is not a temporary file [0]; it is really more of a runtime
data; its location in /tmp is just a historical artefact of a long-wrong
assertion.
Nowadays, distributions either have an actual file as /etc/resolv.conf
(when /etc is writable), or it is a symlink to a location below /run.
Although resolv.conf is used by the C library resolver, a lot of
applications now will directly use it; this is the case for some
container management tools, such as podman (and its helpers, like
netavark), that expect /etc/resolv.conf to either be a file or a symlink
to somewhere in /run, and fail to provide DNS services if that is not
the case.
So, we move the target of /etc/resolv.conf to ../run/resolv.conf.
As a consequence, we can drop the workaround in podman's runtime test.
To be noted: there are tow custom fstab files in Buildroot that do not
explicitly mount a tmpfs on /run:
- one for a systemd runtime test, so /run would also be a tmpfs there
anyway, as systemd does mount one;
- one for the mender_x86_64_efi_defconfig; that's a not a problem:
/ is an ext4 that is mounted r/w (and /tmp is not a tmpfs either, so
the symlink to /tmp would not not have worked if / was not r/w
anyway).
This leaves people with their own fstab, to adapt. Cater to them by
adding a little blurb in the documentation.
Note: the following 43 tests all built and ran successfully:
tests.init
tests.package.test_apache
tests.package.test_docker_compose
tests.package.test_dropbear
tests.package.test_iputils
tests.package.test_podman
tests.package.test_skopeo
tests.package.test_wget
(no other runtime test were attempted)
[0] temporary, as in relatively short-lived.
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Julien Olivain <ju.o@free.fr>
Yann E. MORIN