distroinstaller: Support --initrd-inject for RHEL4 (bz 866608)

RHEL4 kernels are gzip'd ext2 images, so unzip it, use debugfs to inject
files, and zip it back up. Based on shell code from Patrick J. LoPresti.

virtinst/distroinstaller.py

@@ -159,6 +159,61 @@ def _upload_file(conn, meter, destpool, src):
     return vol
 
 
+def _rhel4_initrd_inject(initrd, injections):
+    try:
+        file_proc = subprocess.Popen(["file", "-z", initrd],
+                                     stdout=subprocess.PIPE,
+                                     stderr=subprocess.PIPE)
+        if not "ext2 filesystem" in file_proc.communicate()[0]:
+            return False
+    except:
+        logging.exception("Failed to file command for rhel4 initrd detection")
+        return False
+
+    logging.debug("Is RHEL4 initrd")
+
+    # Uncompress the initrd
+    newinitrd = file(initrd + ".new", "wb")
+    gzip_proc = subprocess.Popen(["gzip", "-d", "-f", "-c", initrd],
+                                 stdout=newinitrd,
+                                 stderr=subprocess.PIPE)
+    gzip_proc.wait()
+    newinitrd.close()
+
+    debugfserr = ""
+    for filename in injections:
+        # We have an ext2 filesystem, use debugfs to inject files
+        cmd = ["debugfs", "-w", "-R",
+               "write %s %s" % (filename, os.path.basename(filename)),
+               newinitrd.name]
+        logging.debug("Copying %s to the initrd with cmd=%s", filename, cmd)
+
+        debugfs_proc = subprocess.Popen(cmd,
+                                        stdout=subprocess.PIPE,
+                                        stderr=subprocess.PIPE)
+        debugfs_proc.wait()
+        debugfserr += debugfs_proc.stderr.read() or ""
+
+    gziperr = gzip_proc.stderr.read()
+    if gziperr:
+        logging.debug("gzip stderr=%s", gziperr)
+    if debugfserr:
+        logging.debug("debugfs stderr=%s", debugfserr)
+
+    # Recompress the initrd
+    gzip_proc = subprocess.Popen(["gzip"],
+                                 stdin=file(newinitrd.name, "rb"),
+                                 stdout=file(initrd, "wb"),
+                                 stderr=subprocess.PIPE)
+    gzip_proc.wait()
+    gziperr = gzip_proc.stderr.read()
+    if gziperr:
+        logging.debug("gzip stderr=%s", gziperr)
+    os.unlink(newinitrd.name)
+
+    return True
+
+
 def _perform_initrd_injections(initrd, injections, scratchdir):
     """
     Insert files into the root directory of the initial ram disk
@@ -166,6 +221,9 @@ def _perform_initrd_injections(initrd, injections, scratchdir):
     if not injections:
         return
 
+    if _rhel4_initrd_inject(initrd, injections):
+        return
+
     tempdir = tempfile.mkdtemp(dir=scratchdir)
     os.chmod(tempdir, 0775)