provisioning-vmware: fix explanation of govc argument limit

[bgilbert]

The relevant limit is OS-dependent and isn't always ARG_MAX. On Linux it's MAX_ARG_STRLEN, and on Windows, cmd.exe and PowerShell impose lower limits than the kernel does.

While we're here, switch gzip to use max compression.

cc @Okeanos

[Okeanos]

The 128 KiB limit you put into the hint is definitely wrong for Windows 10 using Git Bash (regardless of Windows Terminal or MSys2/MinTTY) - in that case the limit appears to be just under 32KiB. That's why I initially wrote "check your env" to see the limit and assumed the ARG_MAX is correct. I'll update my comment later on today with some examples and respective error codes.

Semi-related: once govc 0.27.0 is released we can update the documentation and remove the hint along with a change to using govc vm.change vm-name -f 'key=/path/to/ignition.config.ign' instead of the current -e flag. That works platform independently and the limit is now server side based on the max-body size the ESXi will accept during HTTP requests.

[bgilbert]

Right, thanks, I forgot about non-Linux. Updated!

[Okeanos]

No worries … I had to find out the hard way as well about this which is why I am being extra careful nowadays ;-)

Just did some test on a Windows 10 VM with Windows Terminal + Git Bash and it appears to have an overall limit slightly below 32KiB for the whole command:

The macOS Catalina test with an equally weird value for the limit but slightly larger than 256KiB:

[bgilbert]

Thanks for testing! The macOS limit you found is smaller than 256 KiB, which is 262144 bytes. I wouldn't be surprised if the size of the environment block is also factored into that limit.

[Okeanos]

You are absolutely right 🤦‍♂️ – I really shouldn't be doing math that late in the day. The exact difference is moot, though, because people shaving it that close might just better be served with self-compiling govc from master and use the -f flag. That's what we did to account for our Windows-buddies at my employer.