From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Sat, 29 Aug 2015 03:15:33 +0000 (-0400)
Subject: Update following changes to sys_membarrier ABI
X-Git-Tag: v0.9.0~44
X-Git-Url: https://git.lttng.org/?p=urcu.git;a=commitdiff_plain;h=64f469e628fe45059f091f2808188fb52fa109c9;hp=64f469e628fe45059f091f2808188fb52fa109c9

Update following changes to sys_membarrier ABI

sys_membarrier underwent changes between its original implementation and
its upcoming inclusion into the Linux kernel. Update its use to follow
those changes.

Should the prior user-space code be built against a kernel header that
defines SYS_membarrier, and executed against that kernel, the following
scenarios may happen:

- -1 will be returned with EINVAL errno if the 2nd argument (flags) is
  non-zero (the previous ABI expected a single argument),
- (MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY) defined as
  (1 << 0) | (1 << 16) will return -1 with EINVAL errno, because valid
  commands are now one-hot.

Therefore, should an incompatible user-space code try to use
sys_membarrier, it will simply think that the system does not have
membarrier support due to the negative return value upon query.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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