[PATCH] add libsync.h helper

[Rob Clark]

On Mon, Oct 31, 2016 at 1:23 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Mon, Oct 31, 2016 at 12:43:09PM -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.
>>
>> This is probably mostly used from mesa, but some drivers, test apps, etc
>> may also want to use it from libdrm.
>>
>> v2: handle EINTR, add sync_accumulate() based on #dri-devel discussion,
>>     etc
>>
>> Signed-off-by: Rob Clark <robclark at freedesktop.org>
>> ---
>>  Makefile.sources |   1 +
>>  libsync.h        | 145 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 146 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..2f9aafb
>> --- /dev/null
>> +++ b/libsync.h
>> @@ -0,0 +1,145 @@
>> +/*
>> + *  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 <assert.h>
>> +#include <errno.h>
>> +#include <stdint.h>
>> +#include <string.h>
>> +#include <sys/ioctl.h>
>> +#include <sys/poll.h>
>> +#include <unistd.h>
>> +
>> +#if defined(__cplusplus)
>> +extern "C" {
>> +#endif
>> +
>> +/* duplicated from linux/sync_file.h to avoid build-time dependency
>> + * on new headers
>> + */
>> +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 = {0};
>
> Would have thought you would have gone with fds = { fd, POLLIN }; :)

I'm a bit shakey on what compilers other than gcc would complain
about, so I was actually thinking about going the memset() route to be
super-pedantic..

I do prefer designated initializers but I seem to remember c++ being
unhappy about that.  Not super huge big fan of undesignated
(anonymous?) initializers, but I guess it is probably syscall abi and
not the sort of thing where struct element order could change.. meh?

>> +     int ret;
>> +
>> +     fds.fd = fd;
>> +     fds.events = POLLIN;
>> +
>> +     do {
>> +             ret = poll(&fds, 1, timeout);
>> +             if (ret > 0) {
>> +                     if (fds.revents & (POLLERR | POLLNVAL)) {
>> +                             errno = EINVAL;
>> +                             return -1;
>> +                     }
>> +                     return 0;
>> +             } else if (ret == 0) {
>> +                     errno = ETIME;
>> +                     return -1;
>> +             }
>> +     } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
>> +
>> +     return ret;
>> +}
>> +
>> +static inline int sync_merge(const char *name, int fd1, int fd2)
>> +{
>> +     struct sync_merge_data data = {0};
>> +     int ret;
>> +
>> +     data.fd2 = fd2;
>> +     strncpy(data.name, name, sizeof(data.name));
>> +
>> +     do {
>> +             ret = ioctl(fd1, SYNC_IOC_MERGE, &data);
>> +     } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
>> +
>> +     if (ret < 0)
>> +             return ret;
>> +
>> +     return data.fence;
>> +}
>> +
>> +/* accumulate fd2 into fd1.  If *fd1 is not a valid fd then dup fd2,
>> + * otherwise sync_merge() and close the old *fd1.  This can be used
>> + * to implement the pattern:
>> + *
>> + *    init()
>> + *    {
>> + *       batch.fence_fd = 1;
>
> -1

oh whoops, thx, fixed up locally

BR,
-R

>> + *    }
>> + *
>> + *    // does *NOT* take ownership of fd
>> + *    server_sync(int fd)
>> + *    {
>> + *       if (sync_accumulate("foo", &batch.fence_fd, fd)) {
>> + *          ... error ...
>> + *       }
>> + *    }
>> + */
>> +static inline int sync_accumulate(const char *name, int *fd1, int fd2)
>> +{
>> +     int ret;
>> +
>> +     assert(fd2 >= 0);
>> +
>> +     if (*fd1 < 0) {
>> +             *fd1 = dup(fd2);
>> +             return 0;
>> +     }
>> +
>> +     ret = sync_merge(name, *fd1, fd2);
>> +     if (ret < 0) {
>> +             /* leave *fd1 as it is */
>> +             return ret;
>> +     }
>> +
>> +     close(*fd1);
>> +     *fd1 = ret;
>> +
>> +     return 0;
>> +}
>
> Lgtm, matches how we want to use it.
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre