K 10
svn:author
V 3
cem
K 8
svn:date
V 27
2018-12-11T01:38:50.806049Z
K 7
svn:log
V 528
rc.subr: Implement list_vars without using 'read'

'read' pessimistically read(2)s one byte at a time, which can be quite
silly for large environments in slow emulators.

In my boring user environment, truss shows that the number of read()
syscalls to source rc.subr and invoke list_vars is reduced by something like
3400 to 60.  ministat(1) shows a significant time difference of about -71%
for my environment.

Suggested by:	jilles
Discussed with:	dteske, jhb, jilles
Differential Revision:	https://reviews.freebsd.org/D18481

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