Hey On Mon, Mar 21, 2016 at 6:14 PM, Daniel Vetter <daniel@xxxxxxxx> wrote: > 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@xxxxxxxx> 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@xxxxxxxxxxxxxxxxxx> >> > Cc: Tiago Vignatti <tiago.vignatti@xxxxxxxxx> >> > Cc: Stéphane Marchesin <marcheu@xxxxxxxxxxxx> >> > Cc: David Herrmann <dh.herrmann@xxxxxxxxx> >> > Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx> >> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx> >> > CC: linux-media@xxxxxxxxxxxxxxx >> > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx >> > Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx >> > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx >> > Cc: devel@xxxxxxxxxxxxxxxxxxxx >> > Cc: Hans Verkuil <hverkuil@xxxxxxxxx> >> > Acked-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx> >> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> >> > --- >> > 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. My question was rather about why we do this? Semantics for EINTR are well defined, and with SA_RESTART (default on linux) user-space can ignore it. However, looping on EAGAIN is very uncommon, and it is not at all clear why it is needed? Returning an error to user-space makes sense if user-space has a reason to react to it. I fail to see how EAGAIN on a cache-flush/sync operation helps user-space at all? As someone without insight into the driver implementation, it is hard to tell why.. Any hints? Thanks David -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
