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semctl.2: NOTES: note when 'sempid' is set on various implementations 

See https://bugzilla.kernel.org/show_bug.cgi?id=112271 and
http://thread.gmane.org/gmane.linux.kernel/2162754/
    Subject: [PATCH] Don't set sempid in semctl syscall.
    Newsgroups: gmane.linux.kernel
    Date: 2016-02-26 12:21:38 GMT

Reported-by: Davidlohr Bueso <dave@stgolabs.net>
Reported-by: Manfred Spraul <manfred@colorfullife.com>
Reported-by: Philip Semanchuk <linux_kernel.20.ick@spamgourmet.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-02-28 20:11:22 +01:00
parent 88ee5c1c61
commit 84466c16bd
1 changed files with 46 additions and 6 deletions
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52
man2/semctl.2
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@ -269,12 +269,9 @@ Return the value of
.B sempid
for the
.IR semnum \-th
semaphore of the set
(i.e., the PID of the process that executed the last
.BR semop (2)
call for the
.IR semnum \-th
semaphore of the set).
semaphore of the set.
This is the PID of the process that last performed an operation on
that semaphore (but see NOTES).
The calling process must have read permission on the semaphore set.
.TP
.B GETVAL
@ -535,6 +532,49 @@ implementation dependent (32767).
For greater portability, it is best to always call
.BR semctl ()
with four arguments.
.\"
.SS The sempid value
POSIX.1 defines
.I sempid
as the "process ID of [the] last operation" on a semaphore,
and explicitly notes that this value is set by a successful
.BR semop (2)
call, with the implication that no other interface affects the
.I sempid
value.
While some implementations conform to the behavior specified in POSIX.1,
others do not.
(The fault here probably lies with POSIX.1 inasmuch as it likely failed
to capture the full range of existing implementation behaviors.)
Various other implementations
.\" At least OpenSolaris (and, one supposes, older Solaris) and Darwin
also update
.I sempid
for the other operations that update the value of a semaphore: the
.B SETVAL
and
.B SETALL
operations, as well as the semaphore adjustments performed
on process termination as a consequence of the use of the
.B SEM_UNDO
flag (see
.BR semop (2)).
Linux also updates
.I sempid
for
.BR SETVAL
operations and semaphore adjustments.
However, somewhat inconsistently, it does not update
.I sempid
for
.BR SETALL
operations.
While the
.B SETALL
behavior might be viewed as a bug, the behavior is longstanding,
and is probably unlikely to change.
.SH SEE ALSO
.BR ipc (2),
.BR semget (2),