[Xen-devel] [PATCH] Do not read files at once in pygrub

[Miroslav Rezanina <mrezanin@xxxxxxxxxx>]

If guest kernel or ramdisk image is too large to fit in the dom0 memory, it 
causes pygrub crash with "out of memory" error. 
This patch reads kernel/ramdisk file in 1 MB blocks so prevent exhausting whole 
memory.

Signed-off-by: Miroslav Rezanina <mrezanin@xxxxxxxxxx>

Patch:
--
diff -r 238900a4ed22 tools/pygrub/src/pygrub
--- a/tools/pygrub/src/pygrub   Mon May 21 12:03:32 2012 +0200
+++ b/tools/pygrub/src/pygrub   Tue May 22 11:32:28 2012 +0200
@@ -697,6 +697,20 @@
     def usage():
         print >> sys.stderr, "Usage: %s [-q|--quiet] [-i|--interactive] 
[-n|--not-really] [--output=] [--kernel=] [--ramdisk=] [--args=] [--entry=] 
[--output-directory=] [--output-format=sxp|simple|simple0] <image>" 
%(sys.argv[0],)
 
+    def copy_from_image(fs, file_to_copy, tmp_prefix):
+        (tfd, rv) = tempfile.mkstemp(prefix=tmp_prefix, dir="/var/lib/xen")
+        file_handle = fs.open_file(file_to_copy)
+        readsize = 0
+
+        while True:
+            data = file_handle.read(1048576,readsize)
+            if len(data) == 0:
+                os.close(tfd)
+                return rv
+
  +          readsize += len(data)
+            os.write(tfd,data)          
+
     try:
         opts, args = getopt.gnu_getopt(sys.argv[1:], 'qinh::',
                                    ["quiet", "interactive", "not-really", 
"help", 
@@ -824,21 +838,15 @@
     if not_really:
         bootcfg["kernel"] = "<kernel:%s>" % chosencfg["kernel"]
     else:
-        data = fs.open_file(chosencfg["kernel"]).read()
-        (tfd, bootcfg["kernel"]) = tempfile.mkstemp(prefix="boot_kernel.",
-                                                    dir=output_directory)
-        os.write(tfd, data)
-        os.close(tfd)
+        bootcfg["kernel"] = copy_from_image(fs,chosencfg["kernel"],
+                                            "boot_kernel.")
 
     if chosencfg["ramdisk"]:
         if not_really:
             bootcfg["ramdisk"] = "<ramdisk:%s>" % chosencfg["ramdisk"]
         else:
-            data = fs.open_file(chosencfg["ramdisk"],).read()
-            (tfd, bootcfg["ramdisk"]) = tempfile.mkstemp(
-                prefix="boot_ramdisk.", dir=output_directory)
-            os.write(tfd, data)
-            os.close(tfd)
+            bootcfg["ramdisk"] = copy_from_image(fs, chosencfg["ramdisk",
+                                                 "boot_ramdisk.")
     else:
         initrd = None
 

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