virtinst: quickfix ubuntu net-preseed insert cdrom error

the proper kernel/initrd pair for booting from an http server is found in install/netboot/... on a mounted ubuntu iso.
this last worked in v1.4.2

Discussion: https://github.com/virt-manager/virt-manager/pull/34

(crobinso: add the fetcher.is_iso handling and add a comment)

virtinst/urldetect.py

@@ -30,7 +30,6 @@ class _DistroCache(object):
         self.suse_content = None
         self.debian_media_type = None
 
-
     def acquire_file_content(self, path):
         if path not in self._filecache:
             try:
@@ -133,6 +132,9 @@ class _DistroCache(object):
                 verstr, version, update)
         return version, update
 
+    def fetcher_is_iso(self):
+        return self._fetcher.is_iso()
+
 
 class _SUSEContent(object):
     """
@@ -664,7 +666,16 @@ class DebianDistro(Distro):
             media_type = "daily"
         elif cache.content_regex(".disk/info",
                 "%s.*" % cls._debname.capitalize()):
-            media_type = "disk"
+            # There's two cases here:
+            # 1) Direct access ISO, attached as CDROM afterwards. We
+            #    use one set of kernels in that case which seem to
+            #    assume the prescence of CDROM media
+            # 2) ISO mounted and exported over URL. We use a different
+            #    set of kernels that expect to boot from the network
+            if cache.fetcher_is_iso():
+                media_type = "disk"
+            else:
+                media_type = "mounted_iso_url"
 
         if media_type:
             cache.debian_media_type = media_type
@@ -710,6 +721,8 @@ class DebianDistro(Distro):
         url_prefix = "current/images"
         if self.cache.debian_media_type == "daily":
             url_prefix = "daily"
+        elif self.cache.debian_media_type == "mounted_iso_url":
+            url_prefix = "install"
 
         tree_arch = self._find_treearch()
         hvmroot = "%s/netboot/%s-installer/%s/" % (url_prefix,

virtinst/urlfetcher.py

@@ -26,6 +26,7 @@ class _URLFetcher(object):
     a media source, such as CD ISO, or HTTP/HTTPS/FTP server
     """
     _block_size = 16384
+    _is_iso = False
 
     def __init__(self, location, scratchdir, meter):
         self.location = location
@@ -101,6 +102,12 @@ class _URLFetcher(object):
     # Public API #
     ##############
 
+    def is_iso(self):
+        """
+        If this is a fetcher for local CDROM/ISO
+        """
+        return self._is_iso
+
     def prepareLocation(self):
         """
         Perform any necessary setup
@@ -288,6 +295,7 @@ class _LocalURLFetcher(_URLFetcher):
 
 class _ISOURLFetcher(_URLFetcher):
     _cache_file_list = None
+    _is_iso = True
 
     def _make_full_url(self, filename):
         return "/" + filename