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futex.2: Document FUTEX_LOCK_PI 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Thomas Gleixner 2015-01-14 09:11:16 +01:00 committed by Michael Kerrisk
parent dcdfde2633
commit e0547e70ae
1 changed files with 31 additions and 2 deletions
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man2/futex.2
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@ -632,12 +632,41 @@ arguments are ignored.
.TP
.BR FUTEX_LOCK_PI " (since Linux 2.6.18)"
.\" commit c87e2837be82df479a6bae9f155c43516d2feebc
.\" FIXME to complete
.\"
.\" FIXME Employs 'timeout' argument, with absolute time value on
.\" CLOCK_REALTIME clock; 'timeout' can be NULL
.\"
[As yet undocumented]
This operation reads from the futex address provided by the
.I uaddr
argument, which contains the namespace-specific thread ID (TID)
of the lock owner.
If the TID is 0, then the kernel tries to set the waiter's TID atomically.
If the TID is nonzero or the take over fails,
the kernel sets atomically the
.B FUTEX_WAITERS
bit, which signals the owner that it cannot unlock the futex in
user space atomically by transitioning from TID to 0.
After that, the kernel tries to find the task which is
associated with the owner TID, creates or reuses kernel state on behalf
of the owner and attaches the waiter to it.
The enqueing of the waiter is in descending priority order if more
than one waiter exists.
The owner inherits either the priority or the bandwidth of the waiter.
This inheritance follows the lock chain in the case of
nested locking and performs deadlock detection.
The
.I timeout
.\" FIXME Is this true??????????????????????
argument is handled as described in
.BR FUTEX_WAIT .
The arguments
.IR uaddr2 ,
.IR val ,
and
.IR val3
are ignored.
.TP
.BR FUTEX_UNLOCK_PI " (since Linux 2.6.18)"
.\" commit c87e2837be82df479a6bae9f155c43516d2feebc