"fdinit() fails to initialize newfdp->fd_fd.fd_lastfile to -1. This breaks
fdcopy() which will incorrectly set newfdp->fd_freefile to 1 if no files are
open and the last file descriptor marked as unused for fdp was 0. This later
causes descriptor 0 to be unavailable in newfdp when the optimization is
enabled.
When the last file descriptor previously marked as used is nonzero and marked
as unused, fdunused() incorrectly sets fdp->fd_lastfile to fd - 1 due to
fd_last_used() returning (size - 1). This hides the problem that breaks the
optimization."
This allows us to keep the optimization, while un-breaking it.
This is a RELENG_6 candidate.
PR: kern/87208
MFC after: 1 week
Submitted by: tegge
7448676f59