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 écrit : > >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 > ><christopher.halse.rog...@canonical.com> > >Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch> > >Tested-by: Daniel Vetter <daniel.vet...@ffwll.ch> > >--- > > 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 -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
