linux-kernel - [PATCH] dma-buf: document fd flags and O

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Date:	Mon, 19 Mar 2012 16:41:55 +0100
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	linaro-mm-sig@...ts.linaro.org,
	LKML <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	linux-media@...r.kernel.org
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...il.com>
Subject: [PATCH] dma-buf: document fd flags and O_CLOEXEC requirement

Otherwise subsystems will get this wrong and end up with a second
export ioctl with the flag and O_CLOEXEC support added.

v2: Fixup the function name and caution exporters to limit the flags
to only O_CLOEXEC. Noted by Dave Airlie.

Cc: Dave Airlie <airlied@...il.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@...ll.ch>
---
 Documentation/dma-buf-sharing.txt |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 9f3aeef..a6d4c37 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -319,6 +319,12 @@ Miscellaneous notes
 - Any exporters or users of the dma-buf buffer sharing framework must have
   a 'select DMA_SHARED_BUFFER' in their respective Kconfigs.
 
+- To avoid the wrath of userspace library writers exporting subsystems must have
+  a flag parameter in the ioctl that creates the dma-buf fd which needs to
+  support at least the O_CLOEXEC fd flag. This needs to be passed in the flag
+  parameter of dma_buf_fd. Without any other reasons applying it is recommended
+  that exporters limit the flags passed to dma_buf_fd to only O_CLOEXEC.
+
 References:
 [1] struct dma_buf_ops in include/linux/dma-buf.h
 [2] All interfaces mentioned above defined in include/linux/dma-buf.h
-- 
1.7.7.5

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