From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Peres Subject: Re: [PATCH] dma-buf: Expose buffer size to userspace (v2) Date: Wed, 04 Sep 2013 12:24:27 +0200 Message-ID: <52270A5B.2040600@free.fr> References: <1378264549-9185-1-git-send-email-christopher.halse.rogers@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from smtpfb2-g21.free.fr ([212.27.42.10]:34175 "EHLO smtpfb2-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756240Ab3IDKZU (ORCPT ); Wed, 4 Sep 2013 06:25:20 -0400 In-Reply-To: <1378264549-9185-1-git-send-email-christopher.halse.rogers@canonical.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Christopher James Halse Rogers Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, robclark@gmail.com, linux-media@vger.kernel.org Hi Christopher, Le 04/09/2013 05:15, Christopher James Halse Rogers a =E9crit : > Each dma-buf has an associated size and it's reasonable for userspace > to want to know what it is. > > Since userspace already has an fd, expose the size using the > size =3D lseek(fd, SEEK_END, 0); lseek(fd, SEEK_CUR, 0); > idiom. > > v2: Added Daniel's sugeested documentation, with minor fixups > > Signed-off-by: Christopher James Halse Rogers > Reviewed-by: Daniel Vetter > Tested-by: Daniel Vetter > --- > Documentation/dma-buf-sharing.txt | 12 ++++++++++++ > drivers/base/dma-buf.c | 28 ++++++++++++++++++++++++++++ > 2 files changed, 40 insertions(+) > > diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-bu= f-sharing.txt > index 0b23261..849e982 100644 > --- a/Documentation/dma-buf-sharing.txt > +++ b/Documentation/dma-buf-sharing.txt > @@ -407,6 +407,18 @@ Being able to mmap an export dma-buf buffer obje= ct has 2 main use-cases: > interesting ways depending upong the exporter (if userspace star= ts depending > upon this implicit synchronization). > =20 > +Other Interfaces Exposed to Userspace on the dma-buf FD > +------------------------------------------------------ > + > +- Since kernel 3.12 the dma-buf FD supports the llseek system call, = but only > + with offset=3D0 and whence=3DSEEK_END|SEEK_SET. SEEK_SET is suppor= ted to allow > + the usual size discover pattern size =3D SEEK_END(0); SEEK_SET(0).= Every other > + llseek operation will report -EINVAL. > + > + If llseek on dma-buf FDs isn't support the kernel will report -ESP= IPE for all Shouldn't it be "supported" instead of "support"? Anyway, I'm just curious, in which case is it important to know the siz= e? Do we already have a way to get the dimensions (x, y and stripe)?