Documentation for minimum resize amount

[ultimatespirit]

Looking at the source, and attempting a resize directly, it appears that tomb restricts resizing a tomb to 150MiB increments:

tomb/tomb

Line 2849 in ff69299

_failure "The growth in size must be greater than 150MiB"

This is not reflected in the documentation, and is also a really odd limit. Is there any documentation for why we have such a limit?

Looking at the git blame: 48c08c0

It seems to somehow be related to btrfs, but I am not familiar with any restriction on btrfs's ability to resize arbitrarily that would lend itself to needing a 150MiB minimum. Certainly not finding that at all in its documentation.

Actionable items to consider:

• At least document the limit and why it exists.
• Ideally, why not have these cases fall back on creating a new volume encrypted with the same key file of the requested size and copying contents over?
• If the reason is somehow related to btrfs, detect the filesystem and enforce the limit only for btrfs
• If there's no hard technical reason from filesystems, consider not having the limit.

P.S. It's very odd that btrfs resizing involves creating a directory under $HOME instead of /run/media/$USER/, which is where tomb open normally seems to go:

tomb/tomb

Line 2894 in ff69299

local mp=$HOME/${TOMBNAME}.tomb.resize