[PATCH] dma-buf: Update docs for SYNC ioctl

[Daniel Vetter]

On Mon, Mar 21, 2016 at 01:26:58PM +0100, David Herrmann wrote:
> Hi
> 
> On Mon, Mar 21, 2016 at 8:51 AM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > Just a bit of wording polish plus mentioning that it can fail and must
> > be restarted.
> >
> > Requested by Sumit.
> >
> > v2: Fix them typos (Hans).
> >
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tiago Vignatti <tiago.vignatti at intel.com>
> > Cc: Stéphane Marchesin <marcheu at chromium.org>
> > Cc: David Herrmann <dh.herrmann at gmail.com>
> > Cc: Sumit Semwal <sumit.semwal at linaro.org>
> > Cc: Daniel Vetter <daniel.vetter at intel.com>
> > CC: linux-media at vger.kernel.org
> > Cc: dri-devel at lists.freedesktop.org
> > Cc: linaro-mm-sig at lists.linaro.org
> > Cc: intel-gfx at lists.freedesktop.org
> > Cc: devel at driverdev.osuosl.org
> > Cc: Hans Verkuil <hverkuil at xs4all.nl>
> > Acked-by: Sumit Semwal <sumit.semwal at linaro.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >  Documentation/dma-buf-sharing.txt | 11 ++++++-----
> >  drivers/dma-buf/dma-buf.c         |  2 +-
> >  2 files changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
> > index 32ac32e773e1..ca44c5820585 100644
> > --- a/Documentation/dma-buf-sharing.txt
> > +++ b/Documentation/dma-buf-sharing.txt
> > @@ -352,7 +352,8 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
> >
> >     No special interfaces, userspace simply calls mmap on the dma-buf fd, making
> >     sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always*
> > -   used when the access happens. This is discussed next paragraphs.
> > +   used when the access happens. Note that DMA_BUF_IOCTL_SYNC can fail with
> > +   -EAGAIN or -EINTR, in which case it must be restarted.
> 
> What is "restart on EAGAIN" supposed to mean? Or more generally, what
> does EAGAIN tell the caller?

Do what drmIoctl does essentially.

while (ret == -1 && (errno == EAGAIN || errno == EINTR)
	ret = ioctl();

Typed from memery, too lazy to look it up in the source ;-) I'm trying to
sell the idea of a real dma-buf manpage to Sumit, we should clarify this
in detail there.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch