Before this change we have a mish-mash of ways to pass field names around for
error generation. Sometimes string fieldnames, sometimes .Prefix(), sometimes
neither, often wrong names or not indexed when it should be.
Instead of that mess, this is part one of a couple of commits that will make it
more strongly typed and hopefully encourage correct behavior. At least you
will have to think about field names, which is better than nothing.
It turned out to be really hard to do this incrementally.
Create error, stdin, stdout, stderr streams first, and only start
copying once all the streams have been created. This fixes an issue
where the client immediately starts sending data for stdin before all
the other streams have been created. This ends up blocking the spdy
connection frame handler and causes the entire exec/attach session to
time out.
if LowThresholdPercent > HighThresholdPercent, amountToFree at image_manager.go:208 is negative and image GC will not free memory properly.
Justification:
1) LowThresholdPercent > HighThresholdPercent implies (LowThresholdPercent * capacity / 100) > (HighThresholdPercent * capacity / 100)
2) usage is at least (HighThresholdPercent * capacity / 100)
3) amountToFree = usage - (LowThresholdPercent * capacity / 100)
Combining 1), 2) and 3) implies amountToFree can be negative.
What happens if amountToFree is negative? in freeSpace method, "for _, image := range images " loops at least once
and if everything goes fine, "delete(im.imageRecords, image.id)" is executed.
When checking for condition "if spaceFreed >= bytesToFree", it is always true as bytesToFree is negative
and spaceFreed is positive. The loop is finished, so is image GC.
At the end, only the oldest image is deleted. In situations where there is a lot of dead containers,
each container corresponing to distinct image, number of unused images can get higher.
If two new images get pulled in every 5 minutes, image GC will not work properly and will not free enough space.
Secondly, it will take a lot of time to free all unused images (hours depending on a number of unused images).
This is an incorrect configuration. Image GC should report it and refuse to work.
