This is a bit of a thorny issue. See, the actual `diskSize` variable is
for the *total* disk size, not for the filesystem!
The automatic numbers are meant to compute the *filesystem* required
space. So we have to add any other reserved space!
We have different requirements for reserved space. E.g. there could be
none (when it's actually a filesystem image). There could also be 1MiB
for alignment for an MBR image, legacy+gpt needs 2MiB, then GPT with an
ESP ("bootSize") needs to take the boot partition and GPT size into
account too!
Though luckily(?) for this latter situation we can cheat! As noted in the
change, `bootSize` is NOT the boot partition size. It is actually the
offset where the target filesystem starts.
Reserved space includes:
- inodes space in use (2 blocks per)
- about 5.2% of the space
The 5.2% reserved space was computed empirically when working on a
previous EXT4 image builder. It seems to stabilize around 5% even for
much larger filesystems.
On some filesystems, `du` without `--apparent-size` will not give the
actual size for a file. Using `--apparent-size` will give us the actual
file size.
Though, this is not actually correct still. 1000 × 1 bytes is not 1000
bytes. It is 1000 × ceil(filesize/blockSize)*blockSize.
So instead of adding up the actual file sizes. We are adding up the
block sizes.
Note that this also changes the builder to work with *bytes*, rather
than with any other units. Doing maths on bytes is less likely to go
awry than doing it on other units.
some ban actions need additional packages (eg ipset). since actions can be
provided by the user we need something general that's easy to configure.
we could also enable ipset regardless of the actual configuration of the system
if the iptables firewall is in use (like sshguard does), but that seems very
clumsy and wouldn't easily solve the binary-not-found problems other actions may
also have.
it's not possible to set a different default maxretry value in the DEFAULT jail
because the module already does so. expose the maxretry option to the
configuration to remedy this. (we can't really remove it entirely because
fail2ban defaults to 5)
