lorax: Catch rootfs out of space failures

It isn't always obvious what happened when the rootfs runs out of space,
especially when using lorax via pungi. So this checks for the out of
space error string when building the runtime image and logs it to the
primary logfile and console as an error with the rootfs size.

eg.
2020-01-20 18:52:58,920: The rootfs ran out of space with size=1

src/pylorax/treebuilder.py

@@ -23,6 +23,7 @@ logger = logging.getLogger("pylorax.treebuilder")
 import os, re
 from os.path import basename
 from shutil import copytree, copy2
+from subprocess import CalledProcessError
 from pathlib import Path
 import itertools
 
@@ -228,8 +229,14 @@ class RuntimeBuilder(object):
         workdir = joinpaths(os.path.dirname(outfile), "runtime-workdir")
         os.makedirs(joinpaths(workdir, "LiveOS"))
 
-        imgutils.mkrootfsimg(self.vars.root, joinpaths(workdir, "LiveOS/rootfs.img"),
-                             "Anaconda", size=size)
+        # Catch problems with the rootfs being too small and clearly log them
+        try:
+            imgutils.mkrootfsimg(self.vars.root, joinpaths(workdir, "LiveOS/rootfs.img"),
+                                 "Anaconda", size=size)
+        except CalledProcessError as e:
+            if e.stdout and "No space left on device" in e.stdout:
+                logger.error("The rootfs ran out of space with size=%d", size)
+            raise
 
         # squash the live rootfs and clean up workdir
         imgutils.mksquashfs(workdir, outfile, compression, compressargs)

tests/pylorax/test_imgutils.py

@@ -17,6 +17,7 @@
 import glob
 import os
 import parted
+from subprocess import CalledProcessError
 import tarfile
 import tempfile
 import unittest
@@ -270,6 +271,22 @@ class ImgUtilsTest(unittest.TestCase):
                 file_details = get_file_magic(disk_img.name)
                 self.assertTrue("ext2 filesystem" in file_details, file_details)
 
+    @unittest.skipUnless(os.geteuid() == 0 and not os.path.exists("/.in-container"), "requires root privileges, and no containers")
+    def test_small_mkext4img(self):
+        """Test mkext4img error handling"""
+        with tempfile.TemporaryDirectory(prefix="lorax.test.") as work_dir:
+            with tempfile.NamedTemporaryFile(prefix="lorax.test.disk.") as disk_img:
+                mkfakerootdir(work_dir)
+                # Add a 8MiB file
+                with open(joinpaths(work_dir, "large-file"), "w") as f:
+                    for _ in range(5):
+                        f.write("A" * 1024**2)
+                graft = {work_dir+"/etc/yum.repos.d/": "./tests/pylorax/repos/server-2.repo"}
+                try:
+                    mkext4img(work_dir, disk_img.name, graft=graft, size=5*1024**2)
+                except CalledProcessError as e:
+                    self.assertTrue(e.stdout and "No space left on device" in e.stdout)
+
     @unittest.skipUnless(os.geteuid() == 0 and not os.path.exists("/.in-container"), "requires root privileges, and no containers")
     def test_mkbtrfsimg(self):
         """Test mkbtrfsimg function (requires loop)"""