Don't update bootstrap from image, if possible

There's a new option config_opts['bootstrap_image_ready'] which, if set,
causes that Mock doesn't try to install any tooling into it (silently
expecting that 'dnf' and 'dnf builddep' works inside).

Turns out that e.g. the ubi8 and ubi9 images have the 'builddep' command
installed by default, therefore we can turn this option ON by default.

Fixes: #1088

mock-core-configs/etc/mock/templates/rhel-8.tpl

@@ -4,6 +4,7 @@ config_opts['extra_chroot_dirs'] = [ '/run/lock', ]
 config_opts['releasever'] = '8'
 config_opts['package_manager'] = 'dnf'
 config_opts['bootstrap_image'] = 'registry.access.redhat.com/ubi8/ubi'
+config_opts['bootstrap_image_ready'] = True
 config_opts['description'] = 'RHEL 8'
 
 config_opts['dnf_install_command'] += ' subscription-manager'

mock-core-configs/etc/mock/templates/rhel-9.tpl

@@ -4,6 +4,7 @@ config_opts['dist'] = 'el{{ releasever }}'  # only useful for --resultdir variab
 config_opts['extra_chroot_dirs'] = [ '/run/lock', ]
 config_opts['package_manager'] = 'dnf'
 config_opts['bootstrap_image'] = 'registry.access.redhat.com/ubi{{ releasever }}/ubi'
+config_opts['bootstrap_image_ready'] = True
 config_opts['description'] = 'RHEL {{ releasever }}'
 
 config_opts['dnf_install_command'] += ' subscription-manager'

mock/docs/site-defaults.cfg

@@ -143,6 +143,21 @@
 #config_opts['use_bootstrap_image'] = False
 #config_opts['bootstrap_image'] = 'fedora:latest'
 
+# Mock in a nutshell needs to have the selected config_opts["package_manager"]
+# executable in bootstrap, and "builddep" command working.  That's why Mock
+# automatically installs appropriate packages (e.g. dnf5/dnf5-plugins, if
+# package_manager==dnf5).  If the config_opts["bootstrap_image"] though points
+# to a well-prepared image (no additional packages need to be installed), we
+# can set bootstrap_image_ready to True and Mock then avoids installing
+# packages into the bootstrap chroot.  The initial package manager operation is
+# very expensive (downloading metadata, initializing caches, ...) so setting
+# this to True significantly speeds the bootstrap-from-bootstrap_image
+# preparation.  This can also help work-around some preparation issues, see
+# https://github.com/rpm-software-management/mock/issues/1088
+# "bootstrap_module_setup_commands" and "bootstrap_chroot_additional_packages"
+# options invalidate the effect of this option.
+#config_opts['bootstrap_image_ready'] = False
+
 # anything you specify with 'bootstrap_*' will be copied to bootstrap config
 # e.g. config_opts['bootstrap_system_yum_command'] = '/usr/bin/yum-deprecated' will become
 # config_opts['system_yum_command'] = '/usr/bin/yum-deprecated' for bootstrap config

mock/py/mockbuild/buildroot.py

@@ -26,6 +26,9 @@
 from .podman import Podman
 
 
+# pylint: disable=too-many-lines
+
+
 def noop_in_bootstrap(f):
     # pylint: disable=inconsistent-return-statements
     def wrapper(self, *args, **kwargs):
@@ -420,6 +423,9 @@ def _init_pkg_management(self):
         # The desired package manager.
         pm = self.config['package_manager']
 
+        if self.bootstrap_image_is_ready:
+            return
+
         if self.is_bootstrap:
             update_state = f'installing {pm} tooling'
             cmd = self.config.get(f"{pm}_install_command")
@@ -941,6 +947,43 @@ def delete(self):
     def uses_bootstrap_image(self):
         return self.is_bootstrap and self.use_bootstrap_image
 
+    @property
+    def bootstrap_image_is_ready(self):
+        """
+        True if bootstrap image is in use, bootstrap_image_ready==True, and no
+        config_opts field is set that would invalidate the bootstrap
+        "readiness" state.
+        """
+        if not self.uses_bootstrap_image:
+            return False
+
+        # TODO(praiskup): Can we have heuristic for checking if extracted
+        # buildroot is ready?
+
+        # All the options checked here were copied from the corresponding
+        # `bootstrap_` prefixed config option.
+        if not self.config['image_ready']:
+            self.root_log.info("Bootstrap image not marked ready")
+            return False
+
+        # Per configuration, we think that image is ready-made (e.g. ubi8 images
+        # have the 'dnf builddep' command available by default).  But there
+        # still might be reasons to do some updates.
+        for check_option in [
+            "module_enable", "module_install", "module_setup_commands",
+            "chroot_additional_packages"
+        ]:
+            if self.config.get(check_option):
+                self.root_log.info(
+                    f"Package management in bootstrap (from image) is going to "
+                    f"be updated because config_opts['{check_option}'] is set."
+                )
+                return False
+
+        self.root_log.info("Not updating bootstrap chroot, "
+                           "bootstrap_image_ready=True")
+        return True
+
     @traceLog()
     def install_as_root(self, *deps):
         """ Becomes root user and calls self.install() """

mock/py/mockbuild/config.py

@@ -83,6 +83,7 @@ def setup_default_config_opts():
     config_opts['use_bootstrap'] = True
     config_opts['use_bootstrap_image'] = False
     config_opts['bootstrap_image'] = 'fedora:latest'
+    config_opts['bootstrap_image_ready'] = False
 
     config_opts['internal_dev_setup'] = True