K 10
svn:author
V 8
bdrewery
K 8
svn:date
V 27
2016-08-10T18:19:02.610440Z
K 7
svn:log
V 698
Fix -S with -b not atomically updating the destination file.

With both of these flags, the backup was created via rename(dest, backup)
followed by rename(tmp, dest).  This left the destination file missing
for a moment which contradicts the point of -S.

This fixes a race with installworld where PRECIOUSPROG and PRECIOUSLIB
files (which use -S for installation) would briefly be missing.  In the
case of installing rtld with parallel installworld it could render an
error due to not having rtld present to run install/cp in another
process.

Reported by:	jhb
Reviewed by:	jhb
MFC after:	1 week
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D7451

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