Try to canonicalize the first argument to mount(8)

[trasz]

Summary

Try to realpath(3) the 'special' argument to mount(8), falling over
to the previous behaviour if it fails.

This is something mount_nullfs(8) does, but to me it looks like a good
idea in general.

[mjg]

This is a non-starter imo. For example tmpfs does not do anything with dev and you are expected to pass "tmpfs" as the argument. However, at some point the argument may become meaningful. But then it will be susceptible to getting clobbered if the passed value happens to match a file in cwd.

[kib]

All pseudo fs do not do anything with from/source.
For real filesystems, resolving source is actually useful for users, I believe, but it would be a user-visible change. In fact, I sometimes want the behavior that your patch introduces.

Might be, add a flag to mount(8) to request resolution of source.