qemu-iotests: add qed.py image manipulation utility

The qed.py utility can inspect and manipulate QED image files.  It can
be used for testing to see the state of image metadata and also to
inject corruptions into the image file.  It also has a scrubbing feature
to copy just the metadata out of an image file, allowing users to share
broken image files without revealing data in bug reports.

This has lived in my local repo for a long time but could be useful
to others.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/qed.py

+#!/usr/bin/env python
+#
+# Tool to manipulate QED image files
+#
+# Copyright (C) 2010 IBM, Corp.
+#
+# Authors:
+#  Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
+#
+# This work is licensed under the terms of the GNU GPL, version 2 or later.
+# See the COPYING file in the top-level directory.
+
+import sys
+import struct
+import random
+import optparse
+
+# This can be used as a module
+__all__ = ['QED_F_NEED_CHECK', 'QED']
+
+QED_F_NEED_CHECK = 0x02
+
+header_fmt = '<IIIIQQQQQII'
+header_size = struct.calcsize(header_fmt)
+field_names = ['magic', 'cluster_size', 'table_size',
+               'header_size', 'features', 'compat_features',
+               'autoclear_features', 'l1_table_offset', 'image_size',
+               'backing_filename_offset', 'backing_filename_size']
+table_elem_fmt = '<Q'
+table_elem_size = struct.calcsize(table_elem_fmt)
+
+def err(msg):
+    sys.stderr.write(msg + '\n')
+    sys.exit(1)
+
+def unpack_header(s):
+    fields = struct.unpack(header_fmt, s)
+    return dict((field_names[idx], val) for idx, val in enumerate(fields))
+
+def pack_header(header):
+    fields = tuple(header[x] for x in field_names)
+    return struct.pack(header_fmt, *fields)
+
+def unpack_table_elem(s):
+    return struct.unpack(table_elem_fmt, s)[0]
+
+def pack_table_elem(elem):
+    return struct.pack(table_elem_fmt, elem)
+
+class QED(object):
+    def __init__(self, f):
+        self.f = f
+
+        self.f.seek(0, 2)
+        self.filesize = f.tell()
+
+        self.load_header()
+        self.load_l1_table()
+
+    def raw_pread(self, offset, size):
+        self.f.seek(offset)
+        return self.f.read(size)
+
+    def raw_pwrite(self, offset, data):
+        self.f.seek(offset)
+        return self.f.write(data)
+
+    def load_header(self):
+        self.header = unpack_header(self.raw_pread(0, header_size))
+
+    def store_header(self):
+        self.raw_pwrite(0, pack_header(self.header))
+
+    def read_table(self, offset):
+        size = self.header['table_size'] * self.header['cluster_size']
+        s = self.raw_pread(offset, size)
+        table = [unpack_table_elem(s[i:i + table_elem_size]) for i in xrange(0, size, table_elem_size)]
+        return table
+
+    def load_l1_table(self):
+        self.l1_table = self.read_table(self.header['l1_table_offset'])
+        self.table_nelems = self.header['table_size'] * self.header['cluster_size'] / table_elem_size
+
+    def write_table(self, offset, table):
+        s = ''.join(pack_table_elem(x) for x in table)
+        self.raw_pwrite(offset, s)
+
+def random_table_item(table):
+    vals = [(index, offset) for index, offset in enumerate(table) if offset != 0]
+    if not vals:
+        err('cannot pick random item because table is empty')
+    return random.choice(vals)
+
+def corrupt_table_duplicate(table):
+    '''Corrupt a table by introducing a duplicate offset'''
+    victim_idx, victim_val = random_table_item(table)
+    unique_vals = set(table)
+    if len(unique_vals) == 1:
+        err('no duplication corruption possible in table')
+    dup_val = random.choice(list(unique_vals.difference([victim_val])))
+    table[victim_idx] = dup_val
+
+def corrupt_table_invalidate(qed, table):
+    '''Corrupt a table by introducing an invalid offset'''
+    index, _ = random_table_item(table)
+    table[index] = qed.filesize + random.randint(0, 100 * 1024 * 1024 * 1024 * 1024)
+
+def cmd_show(qed, *args):
+    '''show [header|l1|l2 <offset>]- Show header or l1/l2 tables'''
+    if not args or args[0] == 'header':
+        print qed.header
+    elif args[0] == 'l1':
+        print qed.l1_table
+    elif len(args) == 2 and args[0] == 'l2':
+        offset = int(args[1])
+        print qed.read_table(offset)
+    else:
+        err('unrecognized sub-command')
+
+def cmd_duplicate(qed, table_level):
+    '''duplicate l1|l2 - Duplicate a random table element'''
+    if table_level == 'l1':
+        offset = qed.header['l1_table_offset']
+        table = qed.l1_table
+    elif table_level == 'l2':
+        _, offset = random_table_item(qed.l1_table)
+        table = qed.read_table(offset)
+    else:
+        err('unrecognized sub-command')
+    corrupt_table_duplicate(table)
+    qed.write_table(offset, table)
+
+def cmd_invalidate(qed, table_level):
+    '''invalidate l1|l2 - Plant an invalid table element at random'''
+    if table_level == 'l1':
+        offset = qed.header['l1_table_offset']
+        table = qed.l1_table
+    elif table_level == 'l2':
+        _, offset = random_table_item(qed.l1_table)
+        table = qed.read_table(offset)
+    else:
+        err('unrecognized sub-command')
+    corrupt_table_invalidate(qed, table)
+    qed.write_table(offset, table)
+
+def cmd_need_check(qed, *args):
+    '''need-check [on|off] - Test, set, or clear the QED_F_NEED_CHECK header bit'''
+    if not args:
+        print bool(qed.header['features'] & QED_F_NEED_CHECK)
+        return
+
+    if args[0] == 'on':
+        qed.header['features'] |= QED_F_NEED_CHECK
+    elif args[0] == 'off':
+        qed.header['features'] &= ~QED_F_NEED_CHECK
+    else:
+        err('unrecognized sub-command')
+    qed.store_header()
+
+def cmd_zero_cluster(qed, pos, *args):
+    '''zero-cluster <pos> [<n>] - Zero data clusters'''
+    pos, n = int(pos), 1
+    if args:
+        if len(args) != 1:
+            err('expected one argument')
+        n = int(args[0])
+
+    for i in xrange(n):
+        l1_index = pos / qed.header['cluster_size'] / len(qed.l1_table)
+        if qed.l1_table[l1_index] == 0:
+            err('no l2 table allocated')
+
+        l2_offset = qed.l1_table[l1_index]
+        l2_table = qed.read_table(l2_offset)
+
+        l2_index = (pos / qed.header['cluster_size']) % len(qed.l1_table)
+        l2_table[l2_index] = 1 # zero the data cluster
+        qed.write_table(l2_offset, l2_table)
+        pos += qed.header['cluster_size']
+
+def cmd_copy_metadata(qed, outfile):
+    '''copy-metadata <outfile> - Copy metadata only (for scrubbing corrupted images)'''
+    out = open(outfile, 'wb')
+
+    # Match file size
+    out.seek(qed.filesize - 1)
+    out.write('\0')
+
+    # Copy header clusters
+    out.seek(0)
+    header_size_bytes = qed.header['header_size'] * qed.header['cluster_size']
+    out.write(qed.raw_pread(0, header_size_bytes))
+
+    # Copy L1 table
+    out.seek(qed.header['l1_table_offset'])
+    s = ''.join(pack_table_elem(x) for x in qed.l1_table)
+    out.write(s)
+
+    # Copy L2 tables
+    for l2_offset in qed.l1_table:
+        if l2_offset == 0:
+            continue
+        l2_table = qed.read_table(l2_offset)
+        out.seek(l2_offset)
+        s = ''.join(pack_table_elem(x) for x in l2_table)
+        out.write(s)
+
+    out.close()
+
+def usage():
+    print 'Usage: %s <file> <cmd> [<arg>, ...]' % sys.argv[0]
+    print
+    print 'Supported commands:'
+    for cmd in sorted(x for x in globals() if x.startswith('cmd_')):
+        print globals()[cmd].__doc__
+    sys.exit(1)
+
+def main():
+    if len(sys.argv) < 3:
+        usage()
+    filename, cmd = sys.argv[1:3]
+
+    cmd = 'cmd_' + cmd.replace('-', '_')
+    if cmd not in globals():
+        usage()
+
+    qed = QED(open(filename, 'r+b'))
+    try:
+        globals()[cmd](qed, *sys.argv[3:])
+    except TypeError, e:
+        sys.stderr.write(globals()[cmd].__doc__ + '\n')
+        sys.exit(1)
+
+if __name__ == '__main__':
+    main()