bootloader: Add a zipl bootloader backend

[cgwalters]

zipl is a bit special in that it parses the BLS config files
directly but we need to run the command to update the "boot block".

Hence, we're not generating a separate config file like the other
backends. Instead, extend the bootloader interface with a post_bls_sync
method that is run in the same place we swap the boot/loader symlink.

We write a "stamp file" in /boot that says we need to run this command.
The reason we use stamp file is to prevent the case where the system is
interrupted after BLS file is updated, but before zipl is triggered,
then zipl boot records are not updated.
This opens the door to making things eventually-consistent/reconcilable
by later adding a systemd unit to run zipl if we're interrupted via
a systemd unit - I think we should eventually take this approach
everywhere rather than requiring /boot/loader to be a symlink.

Author: Colin Walters walters@verbum.org
Tested-by: Tuan Hoang tmhoang@linux.ibm.com
Co-Authored-By: Tuan Hoang tmhoang@linux.ibm.com

[cgwalters]

(Only compile tested!)

[Prashanth684]

(Only compile tested!)

i'd like to test these changes locally as part of creating an fcos/rhcos image on s390x. any idea how i can do that ?

[cgwalters]

i'd like to test these changes locally as part of creating an fcos/rhcos image on s390x. any idea how i can do that ?

See https://github.com/coreos/coreos-assembler/blob/master/README-devel.md#using-overrides

[vtolstov]

can you share link to this kind of bootloader - zipl ?

[cgwalters]

can you share link to this kind of bootloader - zipl ?

See https://github.com/ibm-s390-tools/s390-tools/ for https://en.wikipedia.org/wiki/Linux_on_z_Systems

[tuan-hoang1]

Given we make *out_is_active = FALSE; and specifically set sysroot.bootloader zipl in create_disk.sh, I think we still need this, right ?

diff --git a/src/libostree/ostree-repo.c b/src/libostree/ostree-repo.c
index b654aff2..94116290 100644
--- a/src/libostree/ostree-repo.c
+++ b/src/libostree/ostree-repo.c
@@ -3185,7 +3185,7 @@ reload_sysroot_config (OstreeRepo          *self,
      * https://github.com/ostreedev/ostree/issues/1719
      * https://github.com/ostreedev/ostree/issues/1801
      */
-    if (!(g_str_equal (bootloader, "auto") || g_str_equal (bootloader, "none")))
+    if (!(g_str_equal (bootloader, "auto") || g_str_equal (bootloader, "none") || g_str_equal (bootloader, "zipl")))
       return glnx_throw (error, "Invalid bootloader configuration: '%s'", bootloader);
 
     g_free (self->bootloader);

I thought "auto" should cover when we specifically set bootloader, but seems not likely as rpm-ostreed reported
Oct 15 16:40:28 coreos rpm-ostree[1360]: error: Couldn't start daemon: Error setting up sysroot: Invalid bootloader configuration: 'zipl'

[cgwalters]

if (!(g_str_equal (bootloader, "auto") || g_str_equal (bootloader, "none") || g_str_equal (bootloader, "zipl")))

Oh right. Thanks, I merged that bit and added the other bootloaders too for completeness. This bit is ugly...need to rewrite the bootloader stuff, but let's do the easy change for now.

[tuan-hoang1]

To summarize:
Colin's 542f550 commit : add a "zipl" check in libostree/ostree-repo.c
Colin's 5646da4 commit : add _ostree_bootloader_zipl_new() to create bootloader object for zipl case.
My last 2 commits : add a comment to make it clearer for why we do _ostree_bootloader_zipl_new() instead inside libostree/ostree-sysroot-deploy.c. Also update git commit message with some more details.

Colin @cgwalters, thanks a lot for quick turnaround ! This works perfectly well. I think we are good to go now.

[tuan-hoang1]

Looks like there was some permission issue in ostree source tree ? I pulled your remote tree and make a branch on my local repo, maybe that's an issue ? Let me clone your tree then ...

[cgwalters]

Repushed to retrigger CI.

[jlebon]

/lgtm

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[cgwalters]

/retest