[Qemu-devel] [RFC PATCH 3/5] qcow2.py: add load_image() method

[Paolo Bonzini]

The load_image() method optionally probes for the image format
and returns an instance of a subclass of ImageFile.  So far
only qcow2 is supported.

Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
 tests/qemu-iotests/qcow2.py | 44 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 11 deletions(-)

diff --git a/tests/qemu-iotests/qcow2.py b/tests/qemu-iotests/qcow2.py
index 773c947..77e03cb 100755
--- a/tests/qemu-iotests/qcow2.py
+++ b/tests/qemu-iotests/qcow2.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 
 import sys
+import os
 import struct
 import string
 
@@ -20,6 +21,10 @@ class ImageFile:
         self.__dict__ = fields
         self.fd = fd
 
+    def close(self):
+        self.fd.close()
+        self.fd = None
+
     def raw_pread(self, offset, size):
         self.fd.seek(offset)
         return self.fd.read(size)
@@ -28,6 +33,7 @@ class ImageFile:
         self.fd.seek(offset)
         return self.fd.write(data)
 
+
 class Qcow(ImageFile):
 
     uint32_t = 'I'
@@ -58,6 +64,7 @@ class Qcow(ImageFile):
     ];
 
     HEADER_FMT = '>' + ''.join(field[0] for field in fields)
+    QCOW_MAGIC = 0x514649fb
 
     def __init__(self, fd):
 
@@ -71,6 +78,9 @@ class Qcow(ImageFile):
             for i, field in enumerate(Qcow.fields))
 
         ImageFile.__init__(self, fd, fields)
+        if self.magic != Qcow.QCOW_MAGIC:
+            raise Error('not a QCOW2 image')
+
         self.set_defaults()
         self.cluster_size = 1 << self.cluster_bits
 
@@ -155,31 +165,44 @@ class Qcow(ImageFile):
             print "%-25s %s" % ("data", data)
             print ""
 
+def load_image(filename, mode='rb', format=None):
+    fd = open(filename, mode)
+    if format is None:
+        fd.seek(0)
+        buf = fd.read(4)
+        magic = struct.unpack('>I', buf)
+        if magic == Qcow.QCOW_MAGIC:
+            format = 'qcow2'
+        else:
+            format = 'raw'
+
+    if format == 'qcow2':
+        return Qcow(fd)
+
+    raise Error('unknown format %s' % format)
+
 
-def cmd_dump_header(fd):
-    h = Qcow(fd)
+def cmd_dump_header(h):
     h.dump()
     h.dump_extensions()
 
-def cmd_add_header_ext(fd, magic, data):
+def cmd_add_header_ext(h, magic, data):
     try:
         magic = int(magic, 0)
     except:
         print "'%s' is not a valid magic number" % magic
         sys.exit(1)
 
-    h = Qcow(fd)
     h.extensions.append(QcowHeaderExtension.create(magic, data))
     h.update()
 
-def cmd_del_header_ext(fd, magic):
+def cmd_del_header_ext(h, magic):
     try:
         magic = int(magic, 0)
     except:
         print "'%s' is not a valid magic number" % magic
         sys.exit(1)
 
-    h = Qcow(fd)
     found = False
 
     for ex in h.extensions:
@@ -193,7 +216,7 @@ def cmd_del_header_ext(fd, magic):
 
     h.update()
 
-def cmd_set_feature_bit(fd, group, bit):
+def cmd_set_feature_bit(h, group, bit):
     try:
         bit = int(bit, 0)
         if bit < 0 or bit >= 64:
@@ -202,7 +225,6 @@ def cmd_set_feature_bit(fd, group, bit):
         print "'%s' is not a valid bit number in range [0, 64)" % bit
         sys.exit(1)
 
-    h = Qcow(fd)
     if group == 'incompatible':
         h.incompatible_features |= 1 << bit
     elif group == 'compatible':
@@ -223,7 +245,7 @@ cmds = [
 ]
 
 def main(filename, cmd, args):
-    fd = open(filename, "r+b")
+    h = load_image(filename, 'r+b', 'qcow2')
     try:
         for name, handler, num_args, desc in cmds:
             if name != cmd:
@@ -232,11 +254,11 @@ def main(filename, cmd, args):
                 usage()
                 return
             else:
-                handler(fd, *args)
+                handler(h, *args)
                 return
         print "Unknown command '%s'" % cmd
     finally:
-        fd.close()
+        h.close()
 
 def usage():
     print "Usage: %s <file> <cmd> [<arg>, ...]" % sys.argv[0]
-- 
1.8.2