K 10
svn:author
V 3
mjg
K 8
svn:date
V 27
2020-08-11T14:27:57.849156Z
K 7
svn:log
V 228
devfs: rework si_usecount to track opens

This removes a lot of special casing from the VFS layer.

Reviewed by:	kib (previous version)
Tested by:	pho (previous version)
Differential Revision:	https://reviews.freebsd.org/D25612

END