Add a flags argument to wait_for_lock so that O_NONBLOCK can be
passed to open if a user doesn't want the open to sleep until the
lock becomes available.
Submitted by: Amir Shalem (partially modified)
for mutual exclusion:
A brief description of the problem:
1) Proc A picks up non-blocking lock on file X
2) Proc B attempts to pickup lock, fails then waits
3) Proc C attempts to pickup lock, fails then waits
4) Proc A releases lock
5) Proc B acquires lock, release it to pickup a non-blocking version
6) Proc C acquires lock, release it to pickup a non-blocking version
7) Both process B and C race each other to pickup lock again
This occurs mainly because the processes do not keep the lock after they have
been waiting on it. They drop it, attempt to re-acquire it. (They use the wait
to notify when the lock has become available then race to pick it up). This
results in additional CPU utilization during the race, and can also result
in processes picking locks up out of order.
This change attempts to correct this problem by eliminating the test/acquire
race and having the operating system handle it.
Reported by: kris
Tested by: kris
MFC after: 1 week
Split commands into two groups: one with optional count and one with
required argument. Changed synopsis line accordingly.
Added some hopefully-helpful comments based on experiments, knowing
that not all hardware works the same.
PR: docs/84101
Approved by: keramida
MFC after: 3 days
replacement and has additional features which make it superior.
Discussed on: -arch
Reviewed by: thompsa
X-MFC-after: never (RELENG_6 as transition period)
-- Made the synopses more precise.
-- Added argument to flag in option description.
-- Moved -b default and limits to option description (to un-hide).
-- Noted several behaviors that were not mentioned.
-- A few more trivial changes.
PR: docs/46787
Approved by: keramida
MFC after: 3 days
a -B option which causes bpf peers to be printed. This option can be
used in conjunction with -I if information about specific interfaces
is desired. This is similar to what NetBSD added to their version of
netstat.
$ netstat -B
Pid Netif Flags Recv Drop Match Sblen Hblen Command
1137 lo0 p--s-- 0 0 0 0 0 tcpdump
205 sis0 -ifs-l 37331 0 1 0 0 dhclient
$
$ netstat -I lo0 -B
Pid Netif Flags Recv Drop Match Sblen Hblen Command
1174 lo0 p--s-- 0 0 0 0 0 tcpdump
$
-Add bpf.c which stores all the code for retrieving and parsing bpf
related statistics.
-Modify main.c to add support for the -B option and hook it into the
program logic.
-Add bpf.c to the build.
-Document this new functionality in the man page and bump the revision
date.
-Add prototype for bpf_stats function.
