[PATCH libdrm] add libsync.h helper

[Rob Clark]

On Mon, Oct 31, 2016 at 9:55 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 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);

note that if you don't want to leak fd's you'd have to do something more like:

  int new_fence = sync_merge(batch->fence_in, fence);
  if (batch->fence_in != -1)
     close(batch->fence_in);
  batch->fence_in = new_fence;

so it isn't *that* much better..  I guess you could do the close()
unconditionally and ignore the error if batch->fence_in==-1..

BR,
-R

> finished by
>         execbuf(&batch);
>         close(batch.fence_in);
>         batch.fence_in = -1;
> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre