Add kern_unmount(), use in Linuxulator

[trasz]

Summary

Add kern_unmount() and use in Linuxulator. No functional changes.

[kib]

sys/compat/linux/linux_file.c

1083

I am sure that it is not correct. Can we remove this function instead ?

[trasz]

Regen.

[trasz]

sys/compat/linux/linux_file.c

1083

Not really, it's the Linux's main umount2(2) syscall. Should be fixed, though.

[kib]

sys/compat/linux/linux_file.c

1081

Don't you need to check other flags and at least log if anything is set ?

[trasz]

Detect unsupported flags.

[trasz]

sys/compat/linux/linux_file.c

1081

Yeah, we can actually error out on unsupported ones.

[kib]

sys/compat/linux/linux_file.c

1083

What about linux prefix translation ? I see that the old syscall code did not do that, why ?

[trasz]

Why would it? It doesn't make much sense; you want it to unmount what you pass as an argument, and not it's linuxulator counterpart. Besides; this is mostly for use inside jails/chroots.

[kib]

In D22646#510845, @trasz wrote:

Why would it? It doesn't make much sense; you want it to unmount what you pass as an argument, and not it's linuxulator counterpart. Besides; this is mostly for use inside jails/chroots.

Because this is the consistent behavior. BTW, linux_mount also needs the same fix.