agent_ssh driver did not check RAM size

[Haomeng,Wang]

agent_ssh will download the image from glance via *swift_temp_url* into in-memory-folder /tmp/<img_id> first then run 'qemu-img' to 'copy' image to local harddisk.

However if the RAM size is less than the converted image, will break the ipa deployments as below log:

ir-cond.log:2015-06-26 07:28:27.258 ERROR ironic.drivers.modules.agent [-] node db1a8a8f-885d-4433-a772-551f917457f0 command status errored: {u'message': u'Error downloading image.', u'code': 500, u'type': u'ImageDownloadError', u'details': u'Download of image id e18a422d-94d8-4389-b345-21be90b6f745 failed: Unable to write image to /tmp/e18a422d-94d8-4389-b345-21be90b6f745. Error: [Errno 28] No space left on device'}

[Haomeng,Wang (whaom)]

And it is better that we detect the *real* image size in raw format, that can be as input to compare with the physical RAM size to see if it is enough, any comments?

[Dmitry Tantsur (divius)]

I think we should stream an image to the hard drive instead of downloading it into RAM...

[Zhenguo Niu (niu-zglinux)]

@Dmitry Tantsur if the image format is not raw, we need to download the whole image and convert it before write to disk.

[Lucas Alvares Gomes (lucasagomes)]

I think we can convert it on the flight no? With qemu-img... worth investigating

[Ramakrishnan G (rameshg87) (rameshg87)]

As far as I know, it's not possible for qemu-img to convert on the fly.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=513451

>> This is technically not possible. Given the formats involved, the file
>> is not read/written linearly, which render the use of stdin/stdout
>> impossible. Tagging the bug as wontfix.

[Zhenguo Niu (niu-zglinux)]

yeah, I agree we can't convert on the fly, so I'd like to add check for the node ram property and the image.min_disk before provisioning, when using agent deploy.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/215254

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/215254
Committed: https://git.openstack.org/cgit/openstack/ironic/commit/?id=a715e3dcf94af4cd94ba5a51b745d411bc473182
Submitter: Jenkins
Branch: master

commit a715e3dcf94af4cd94ba5a51b745d411bc473182
Author: Zhenguo Niu <email address hidden>
Date: Fri Aug 21 01:11:12 2015 +0800

    Check image size before provisioning for agent driver

    agent will download the image from glance into in-memory-folder first
    then run 'qemu-img' to 'copy' image to local harddisk, but if the RAM
    size is less than the (image size + reserved RAM size), will break the
    IPA deployments.

    Change-Id: I5ed62a8936e996ffed60c811bd01d3be97f95547
    Closes-Bug: #1471081