An operation for filesystem tucking

Posted Mar 31, 2023 20:24 UTC (Fri) by NYKevin (subscriber, #129325)
In reply to: An operation for filesystem tucking by jreiser
Parent article: An operation for filesystem tucking

> For example, if the unmount of the old overlay occurs while rtld, the run-time dynamic linker, is loading a list of shared libraries into an address space, then it may be easy to trigger an incompatibility between libraries at the beginning of the list versus libraries at the end.

As far as I can tell, this is simply illegal. umount(8) says this:

> Note that a filesystem cannot be unmounted when it is 'busy' - for example, when there are open files on it[...]

As long as the loader has at least one file in the mount open, it cannot be unmounted, at least according to this man page.

This is probably also why they want to tuck the new mount underneath the old mount, instead of putting it on top - umount(2) already provides flags for doing a "lazy" unmount that avoids busyness problems, but there is no such thing as a "lazy" mount(2).