Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762502Ab3IDM3o (ORCPT ); Wed, 4 Sep 2013 08:29:44 -0400 Received: from smtp3-g21.free.fr ([212.27.42.3]:36175 "EHLO smtp3-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754209Ab3IDM3l (ORCPT ); Wed, 4 Sep 2013 08:29:41 -0400 Message-ID: <522727A4.6050109@free.fr> Date: Wed, 04 Sep 2013 14:29:24 +0200 From: Martin Peres User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130806 Thunderbird/17.0.8 MIME-Version: 1.0 To: Christopher James Halse Rogers , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, robclark@gmail.com, linux-media@vger.kernel.org Subject: Re: [PATCH] dma-buf: Expose buffer size to userspace (v2) References: <1378264549-9185-1-git-send-email-christopher.halse.rogers@canonical.com> <52270A5B.2040600@free.fr> <20130904120504.GB28675@phenom.ffwll.local> In-Reply-To: <20130904120504.GB28675@phenom.ffwll.local> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2470 Lines: 50 Le 04/09/2013 14:05, Daniel Vetter a ?crit : > On Wed, Sep 04, 2013 at 12:24:27PM +0200, Martin Peres wrote: >> Hi Christopher, >> Le 04/09/2013 05:15, Christopher James Halse Rogers a ?crit : >>> 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 = 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-buf-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 object has 2 main use-cases: >>> interesting ways depending upong the exporter (if userspace starts depending >>> upon this implicit synchronization). >>> +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=0 and whence=SEEK_END|SEEK_SET. SEEK_SET is supported to allow >>> + the usual size discover pattern size = 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 -ESPIPE for all >> Shouldn't it be "supported" instead of "support"? >> >> Anyway, I'm just curious, in which case is it important to know the size? >> Do we already have a way to get the dimensions (x, y and stripe)? > Size is an invariant part of a dma-buf. Everything else wrt metadata isn't > tracked in the kernel, so doesn't make much sense to expose it ;-) > -Daniel ACK, thanks Daniel. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/