Introduce --cache-only boolean option, propagate to modules

Along the way, add basic support for handling boolean
values in python and shell scripts in modules.

[dsd: trivial tweaks: renamed to --cache-only, use variable presence in
 environment for boolean testing, add documentation]

4 files changed, 45 insertions, 4 deletions

diff --git a/doc/README b/doc/README
index ad79946..7a46796 100644
--- a/doc/README
+++ b/doc/README
@@ -54,7 +54,31 @@ release was made.
 
 
 Usage:
-	olpc-os-builder <path to build config> [path to build config...]
+	olpc-os-builder [options] <path to build config> [path to build config...]
+
+
+Offline use:
+
+olpc-os-builder naturally involves a fair amount of downloading in its work.
+These downloads are cached, meaning that while the first run will do a lot
+of downloading, subsequent runs will reuse the locally cached content.
+
+However, those subsequent runs will still go online in order to check that
+cached content is up-to-date. This can be time consuming, especially
+on slow connections.
+
+If you want olpc-os-builder to trust its local caches, and not even go
+online to check that they are current, you can provide the --cache-only
+command-line option.
+
+For obvious reasons, cache-only mode requires you to have previously run
+the same build configuration in "normal" mode beforehand (i.e. without
+--cache-only specified), so that caches are populated.
+
+Be aware that less cache validation is performed during --cache-only runs.
+This means that corrupt caches or truncated files could be treated as good
+in cache-only mode, whereas such problems are generally detected and
+corrected when connectivity is used.
 
 
 Configuration:
diff --git a/lib/ooblib.py b/lib/ooblib.py
index 8d6dd2d..13babbc 100644
--- a/lib/ooblib.py
+++ b/lib/ooblib.py
@@ -17,6 +17,8 @@ fsmount = os.environ['OOB__fsmount']
 
 METADATA_NS = "http://linux.duke.edu/metadata/common"
 
+cacheonly = 'OOB__cacheonly' in os.environ
+
 def read_config(module, option):
     vname = "CFG_%s__%s" % (module, option)
     if not vname in os.environ:
diff --git a/lib/shlib.sh b/lib/shlib.sh
index 34982b0..11324c2 100644
--- a/lib/shlib.sh
+++ b/lib/shlib.sh
@@ -7,6 +7,7 @@ libdir=$OOB__libdir
 bindir=$OOB__bindir
 builddir=$OOB__builddir
 cachedir=$OOB__cachedir
+cacheonly=$OOB__cacheonly
 intermediatesdir=$OOB__intermediatesdir
 outputdir=$OOB__outputdir
 statedir=$OOB__statedir
@@ -78,4 +79,3 @@ install_sugar_bundle() {
 	mkdir -p "$intermediatesdir/shared/sugar-bundles"
 	ln_or_cp "$1" "$intermediatesdir/shared/sugar-bundles"
 }
-
diff --git a/osbuilder.py b/osbuilder.py
index 0cddd94..ce8e723 100755
--- a/osbuilder.py
+++ b/osbuilder.py
@@ -71,6 +71,9 @@ class Stage(object):
 
         env['oob_config_dir'] = os.path.dirname(self.osb.build_configs[0])
 
+        if self.osb.cacheonly:
+            env['OOB__cacheonly'] = 'True'
+
         envpath = env['PATH'].split(':')
         for dir in ('/sbin', '/usr/sbin'):
             if envpath.count(dir) == 0:
@@ -278,6 +281,9 @@ class OsBuilder(object):
         self.statedir = os.path.join(self.builddir, 'state')
         self.fsmount = os.path.join(self.builddir, 'mnt-fs')
 
+        # gets set in build()
+        self.cacheonly = False
+
         # load config to find module list
         # and set interpolation default for oob_config_dir
         self.cfg = SafeConfigParser({'oob_config_dir':
@@ -363,13 +369,17 @@ class OsBuilder(object):
         # cleanup stage not listed here as its a bit of a special case
     )
 
-    def build(self, clean_output=True, clean_intermediates=True):
+    def build(self, clean_output=True, clean_intermediates=True, cacheonly=False):
         # cleanup from previous runs
         if clean_intermediates and os.path.exists(self.intermediatesdir):
             shutil.rmtree(self.intermediatesdir)
         if clean_output and os.path.exists(self.outputdir):
             shutil.rmtree(self.outputdir)
 
+        self.cacheonly = cacheonly
+        if cacheonly and not os.path.exists(self.cachedir):
+            raise OsBuilderException("Missing cache, cannot use --cache-only")
+
         for dir in (self.builddir, self.cachedir, self.intermediatesdir,
                     self.outputdir, self.statedir, self.fsmount):
             if not os.path.exists(dir):
@@ -407,6 +417,10 @@ def main():
     op.add_option('--no-clean-intermediates', dest="clean_intermediates",
                   action="store_false", default=True,
                   help="Don't clean intermediates directory on startup or exit")
+    op.add_option('--cache-only', dest="cacheonly",
+                  action="store_true", default=False,
+                  help="Run entirely from cache")
+
     (options, args) = op.parse_args()
 
     if len(args) < 1:
@@ -415,7 +429,8 @@ def main():
     try:
         osb = OsBuilder(args)
         osb.build(clean_output=options.clean_output,
-                  clean_intermediates=options.clean_intermediates)
+                  clean_intermediates=options.clean_intermediates,
+                  cacheonly=options.cacheonly)
     except OsBuilderException, e:
         print >>sys.stderr, "ERROR:", e
         sys.exit(1)