K 10
svn:author
V 8
cperciva
K 8
svn:date
V 27
2020-08-26T19:26:48.162105Z
K 7
svn:log
V 924
Add -w option to lockf(1).

By default, lockf(1) opens its lock file O_RDONLY|O_EXLOCK.  On NFS, if the
file already exists, this is split into opening the file read-only and then
requesting an exclusive lock -- and the second step fails because NFS does
not permit exclusive locking on files which are opened read-only.

The new -w option changes the open flags to O_WRONLY|O_EXLOCK, allowing it
to work on NFS -- at the cost of not working if the file cannot be opened
for writing.

(Whether the traditional BSD behaviour of allowing exclusive locks to be
obtained on a file which cannot be opened for writing is a good idea is
perhaps questionable since it may allow less-privileged users to perform
a local denial of service; however this behaviour has been present for a
long time and changing it now seems like it would cause problems.)

Reviewed by:	rmacklem
Differential Revision:	https://reviews.freebsd.org/D26005

END