--wrap symbol
Use a wrapper function for symbol. Any undefined reference to
symbol will be resolved to wrap_symbol. Any
undefined reference to real_symbol will be resolved to
symbol.

This can be used to provide a wrapper for a system function. The
wrapper function should be called wrap_symbol. If it
wishes to call the system function, it should call
real_symbol.

Here is a trivial example:

Host avel.cain
User root
HostName 203.0.113.59
PreferredAuthentications publickey
IdentityFile ~/.ssh/avel
ProxyCommand ssh cain nc %h %p 2> /dev/null

Linus Torvalds said of this issue:

"As to the whole 'hybrid kernel' thing - it's just marketing. It's 'oh, those microkernels had good PR, how can we try to get good PR for our working kernel? Oh, I know, let's use a cool name and try to imply that it has all the PR advantages that that other system has'."