[Qemu-block] [PATCH for-2.6? v2] qemu-iotests: iotests: fail hard if not run via "check"

[Sascha Silbe]

Running an iotests-based Python test directly might appear to work,
but may fail in subtle ways and is insecure:

- It creates files with predictable file names in a world-writable
  location (/var/tmp).

- Tests expect the environment to be set up by check. E.g. 041 and 055
  may take the wrong code paths if QEMU_DEFAULT_MACHINE is not
  set. This can lead to false negatives.

Instead fail hard and tell the user we want to be run via "check".

The actual environment expected by the tests is currently only defined
by the implementation of "check". We use two of the environment
variables set by "check" as indication of whether we're being run via
"check". Anyone writing their own test runner (replacing "check") will
need to replicate the full environment (in a broader sense, not just
environment variables) provided by "check" anyway, including setting
the two environment variables we check. Whereas a regular developer
just trying to invoke the tests usually won't have both of these
defined in their environment so we can catch their mistake and give
out useful advice.

Signed-off-by: Sascha Silbe <address@hidden>
Reviewed-by: Bo Tu <address@hidden>
---
v1→v2:
  - Add comment indicating that it's not just TEST_DIR and
    QEMU_DEFAULT_MACHINE that need to be set. Amend commit message in
    a similar way.

@Tu Bo: I'm assuming your Reviewed-By: still stands as I only added
more information on the background of the change and the check.
---
 tests/qemu-iotests/iotests.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 0c0b533..054b482 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -46,7 +46,7 @@ if os.environ.get('QEMU_OPTIONS'):
 
 imgfmt = os.environ.get('IMGFMT', 'raw')
 imgproto = os.environ.get('IMGPROTO', 'file')
-test_dir = os.environ.get('TEST_DIR', '/var/tmp')
+test_dir = os.environ.get('TEST_DIR')
 output_dir = os.environ.get('OUTPUT_DIR', '.')
 cachemode = os.environ.get('CACHEMODE')
 qemu_default_machine = os.environ.get('QEMU_DEFAULT_MACHINE')
@@ -441,6 +441,14 @@ def verify_quorum():
 def main(supported_fmts=[], supported_oses=['linux']):
     '''Run tests'''
 
+    # We are using TEST_DIR and QEMU_DEFAULT_MACHINE as proxies to
+    # indicate that we're not being run via "check". There may be
+    # other things set up by "check" that individual test cases rely
+    # on.
+    if test_dir is None or qemu_default_machine is None:
+        sys.stderr.write('Please run this test via the "check" script\n')
+        sys.exit(os.EX_USAGE)
+
     debug = '-d' in sys.argv
     verbosity = 1
     verify_image_format(supported_fmts)
-- 
1.9.1