[PATCH libdrm] add libsync.h helper

[Chris Wilson]

On Mon, Oct 31, 2016 at 09:44:07AM -0400, Rob Clark wrote:
> From: Rob Clark <robclark at freedesktop.org>
> 
> Rather than cut/pasting these couple ioctl wrappers everywhere, just
> stuff them as static-inline into a header.
> 
> Signed-off-by: Rob Clark <robclark at freedesktop.org>
> ---
> This is probably mostly used from mesa, but some drivers, test apps, etc
> may also want to use it from libdrm.
> 
>  Makefile.sources |  1 +
>  libsync.h        | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
>  create mode 100644 libsync.h
> 
> diff --git a/Makefile.sources b/Makefile.sources
> index a57036a..10aa1d0 100644
> --- a/Makefile.sources
> +++ b/Makefile.sources
> @@ -13,6 +13,7 @@ LIBDRM_FILES := \
>  	util_math.h
>  
>  LIBDRM_H_FILES := \
> +	libsync.h \
>  	xf86drm.h \
>  	xf86drmMode.h
>  
> diff --git a/libsync.h b/libsync.h
> new file mode 100644
> index 0000000..fc23b7f
> --- /dev/null
> +++ b/libsync.h
> @@ -0,0 +1,74 @@
> +/*
> + *  sync abstraction
> + *  Copyright 2015-2016 Collabora Ltd.
> + *
> + *  Based on the implementation from the Android Open Source Project,
> + *
> + *  Copyright 2012 Google, Inc
> + *
> + *  Permission is hereby granted, free of charge, to any person obtaining a
> + *  copy of this software and associated documentation files (the "Software"),
> + *  to deal in the Software without restriction, including without limitation
> + *  the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + *  and/or sell copies of the Software, and to permit persons to whom the
> + *  Software is furnished to do so, subject to the following conditions:
> + *
> + *  The above copyright notice and this permission notice shall be included in
> + *  all copies or substantial portions of the Software.
> + *
> + *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> + *  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + *  OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + *  ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + *  OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#ifndef _LIBSYNC_H
> +#define _LIBSYNC_H
> +
> +#include <stdint.h>
> +#include <string.h>
> +#include <sys/ioctl.h>
> +#include <sys/poll.h>
> +
> +// todo prob should just #include <linux/sync_file.h> ?
> +struct sync_merge_data {
> +	char	name[32];
> +	int32_t	fd2;
> +	int32_t	fence;
> +	uint32_t	flags;
> +	uint32_t	pad;
> +};
> +#define SYNC_IOC_MAGIC		'>'
> +#define SYNC_IOC_MERGE		_IOWR(SYNC_IOC_MAGIC, 3, struct sync_merge_data)
> +
> +
> +
> +static inline int sync_wait(int fd, int timeout)
> +{
> +	struct pollfd fds;
> +
> +	fds.fd = fd;
> +	fds.events = POLLIN | POLLERR;

POLLERR is implied and ignored in fds.events.

> +	return poll(&fds, 1, timeout);

Returns: -1 on error, 0 on timeout, 1 if signaled.

This function is horrible wrt to -EINTR for example :) Hmm, mixing
poll() and looping over signals until timeout doesn't look as
straightforward.

> +}
> +
> +static inline int sync_merge(const char *name, int fd1, int fd2)
> +{
> +	struct sync_merge_data data = {};
> +	int err;

What I liked was doing

if (fd2 < 0)
	return dup(fd1);

if (fd1 < 0)
	return dup(fd2);

That makes accumulating the fences in the caller much easier (i.e. they
start with
	batch.fence_in = -1;
then
	batch.fence_in = sync_merge(batch.fence_in, fence);
finished by
	execbuf(&batch);
	close(batch.fence_in);
	batch.fence_in = -1;
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre