Phase II in disk state saving for swapout.
Exec summary: after this checkin, the infrastructure exists (once enabled) to create swapout-time "delta" images for all machines in experiments. There is only a single, cumulative swap image per node (i.e., all diffs are from the base image, not from the previous swap). What doesn't yet exist, is the mechanism for reloading the delta at swapin time. That is Phase III. The nitty-gritty: 1. Keep disk image signature files for all nodes in an experiment. New fields in the DB to track, for each disk partition, what image the partition was loaded from. This enables us at swapin or os_load time to create signature files in /proj/<pid>/exp/<eid>/swapinfo for the current contents of a node disk/partition. All nodes with the same image loaded will share (via symlink) the same signature file. TODO: no longer referenced signature files should be removed. Signature info is only collected in the swapinfo directory if the experiment is set to have disk state saving enabled (see #5 below). Info consists of the <vname>.sig file, which is the file created by imagehash, and <vname>.part which says what the root disk is for the node and whether to look at the whole disk or just a single partition when crafting the delta image. 2. Swapout-time hook for creating swapout image. If the experiment is marked as allowing disk state saving, tbswap will arrange to run and then monitor the create-swapimage command on each node. This script will run the modified version of imagezip which uses the signature file to create a delta image. The command to run and maximum timeout are specified via sitevars (previously checked in). Note that the tbswap script currently has special knowledge of /usr/local/bin/create-swapimage as a swapout time script. If the swap/swapout_command sitevar is set to that, Magic Stuff shall occur (i.e. it will monitor the command and make periodic reports of progress). The sitevars are a total hack and will disappear at some point. 3. Client-side script for creating swapout image. os/create-swapimage, very similar to create-image. Uses the info stashed in /proj/..blahblah../swapinfo to create a delta image. XXX fer now hack: the script first looks in /proj/<pid>/bin for an imagezip binary to use. Failing that, it uses the one in the MFS. This allows for easier development of the imagezip changes (i.e., don't have to update the MFS every time. 4. Auto creation of signature files for new images. The create_image script (the one that runs on boss when creating images for users) has been modified to automatically create a signature via imagehash. The .sig file winds up in /usr/testbed/images/sigs or in /proj/<pid>/images/sigs. From there it will be copied at swapin/os_load time to the per-expt swapinfo directory for any node that uses the images. The process for creating standard system images (aka, "Mike") has not yet been modified. When the image creation/installation procedure is formalized into a script, this will be done. 5. Web changes to set/clear saving of disk state at swapout time. Add a checkbox to the experiment create page to allow setting "save swap state". Also added to the experiment modify page, but currently "if (0)"ed out as it will need some additional support. The showstuff page will show it. Taking a page from Leigh's hack book, if EXPOSESTATESAVE in defs.php3 is set to zero (as it is now), then the checkbox doesn't appear in the create experiment page except for STUDLY users.
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