[openstack-dev] [nova] [glance] How to deal with aborted image read?

Chris Friesen chris.friesen at windriver.com
Thu Jun 4 17:46:01 UTC 2015

On 06/04/2015 03:01 AM, Flavio Percoco wrote:
> On 03/06/15 16:46 -0600, Chris Friesen wrote:
>> We recently ran into an issue where nova couldn't write an image file due to
>> lack of space and so just quit reading from glance.
>> This caused glance to be stuck with an open file descriptor, which meant that
>> the image consumed space even after it was deleted.
>> I have a crude fix for nova at "https://review.openstack.org/#/c/188179/"
>> which basically continues to read the image even though it can't write it.
>> That seems less than ideal for large images though.
>> Is there a better way to do this?  Is there a way for nova to indicate to
>> glance that it's no longer interested in that image and glance can close the
>> file?
>> If I've followed this correctly, on the glance side I think the code in
>> question is ultimately glance_store._drivers.filesystem.ChunkedFile.__iter__().
> Actually, to be honest, I was quite confused by the email :P
> Correct me if I still didn't understand what you're asking.
> You ran out of space on the Nova side while downloading the image and
> there's a file descriptor leak somewhere either in that lovely (sarcasm)
> glance wrapper or in glanceclient.

The first part is correct, but the file descriptor is actually held by glance-api.

> Just by reading your email and glancing your patch, I believe the bug
> might be in glanceclient but I'd need to five into this. The piece of
> code you'll need to look into is[0].
> glance_store is just used server side. If that's what you meant -
> glance is keeping the request and the ChunkedFile around - then yes,
> glance_store is the place to look into.
> [0]
> https://github.com/openstack/python-glanceclient/blob/master/glanceclient/v1/images.py#L152

I believe what's happening is that the ChunkedFile code opens the file and 
creates the iterator.  Nova then starts iterating through the file.

If nova (or any other user of glance) iterates all the way through the file then 
the ChunkedFile code will hit the "finally" clause in __iter__() and close the 
file descriptor.

If nova starts iterating through the file and then stops (due to running out of 
room, for example), the ChunkedFile.__iter__() routine is left with an open file 
descriptor.  At this point deleting the image will not actually free up any space.

I'm not a glance guy so I could be wrong about the code.  The externally-visible 
data are:
1) glance-api is holding an open file descriptor to a deleted image file
2) If I kill glance-api the disk space is freed up.
3) If I modify nova to always finish iterating through the file the problem 
doesn't occur in the first place.


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