libsync.h

   1 /*
   2  *  sync abstraction
   3  *  Copyright 2015-2016 Collabora Ltd.
   4  *
   5  *  Based on the implementation from the Android Open Source Project,
   6  *
   7  *  Copyright 2012 Google, Inc
   8  *
   9  *  Permission is hereby granted, free of charge, to any person obtaining a
  10  *  copy of this software and associated documentation files (the "Software"),
  11  *  to deal in the Software without restriction, including without limitation
  12  *  the rights to use, copy, modify, merge, publish, distribute, sublicense,
  13  *  and/or sell copies of the Software, and to permit persons to whom the
  14  *  Software is furnished to do so, subject to the following conditions:
  15  *
  16  *  The above copyright notice and this permission notice shall be included in
  17  *  all copies or substantial portions of the Software.
  18  *
  19  *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  22  *  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  23  *  OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  24  *  ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  25  *  OTHER DEALINGS IN THE SOFTWARE.
  26  */
  27
  28 #ifndef _LIBSYNC_H
  29 #define _LIBSYNC_H
  30
  31 #include <assert.h>
  32 #include <errno.h>
  33 #include <stdint.h>
  34 #include <string.h>
  35 #include <sys/ioctl.h>
  36 #include <sys/poll.h>
  37 #include <unistd.h>
  38
  39 #if defined(__cplusplus)
  40 extern "C" {
  41 #endif
  42
  43 #ifndef SYNC_IOC_MERGE
  44 /* duplicated from linux/sync_file.h to avoid build-time dependency
  45  * on new (v4.7) kernel headers.  Once distro's are mostly using
  46  * something newer than v4.7 drop this and #include <linux/sync_file.h>
  47  * instead.
  48  */
  49 struct sync_merge_data {
  50         char    name[32];
  51         int32_t fd2;
  52         int32_t fence;
  53         uint32_t        flags;
  54         uint32_t        pad;
  55 };
  56 #define SYNC_IOC_MAGIC          '>'
  57 #define SYNC_IOC_MERGE          _IOWR(SYNC_IOC_MAGIC, 3, struct sync_merge_data)
  58 #endif
  59
  60
  61 static inline int sync_wait(int fd, int timeout)
  62 {
  63         struct pollfd fds = {0};
  64         int ret;
  65
  66         fds.fd = fd;
  67         fds.events = POLLIN;
  68
  69         do {
  70                 ret = poll(&fds, 1, timeout);
  71                 if (ret > 0) {
  72                         if (fds.revents & (POLLERR | POLLNVAL)) {
  73                                 errno = EINVAL;
  74                                 return -1;
  75                         }
  76                         return 0;
  77                 } else if (ret == 0) {
  78                         errno = ETIME;
  79                         return -1;
  80                 }
  81         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
  82
  83         return ret;
  84 }
  85
  86 static inline int sync_merge(const char *name, int fd1, int fd2)
  87 {
  88         struct sync_merge_data data = {0};
  89         int ret;
  90
  91         data.fd2 = fd2;
  92         strncpy(data.name, name, sizeof(data.name));
  93
  94         do {
  95                 ret = ioctl(fd1, SYNC_IOC_MERGE, &data);
  96         } while (ret == -1 && (errno == EINTR || errno == EAGAIN));
  97
  98         if (ret < 0)
  99                 return ret;
 100
 101         return data.fence;
 102 }
 103
 104 /* accumulate fd2 into fd1.  If *fd1 is not a valid fd then dup fd2,
 105  * otherwise sync_merge() and close the old *fd1.  This can be used
 106  * to implement the pattern:
 107  *
 108  *    init()
 109  *    {
 110  *       batch.fence_fd = -1;
 111  *    }
 112  *
 113  *    // does *NOT* take ownership of fd
 114  *    server_sync(int fd)
 115  *    {
 116  *       if (sync_accumulate("foo", &batch.fence_fd, fd)) {
 117  *          ... error ...
 118  *       }
 119  *    }
 120  */
 121 static inline int sync_accumulate(const char *name, int *fd1, int fd2)
 122 {
 123         int ret;
 124
 125         assert(fd2 >= 0);
 126
 127         if (*fd1 < 0) {
 128                 *fd1 = dup(fd2);
 129                 return 0;
 130         }
 131
 132         ret = sync_merge(name, *fd1, fd2);
 133         if (ret < 0) {
 134                 /* leave *fd1 as it is */
 135                 return ret;
 136         }
 137
 138         close(*fd1);
 139         *fd1 = ret;
 140
 141         return 0;
 142 }
 143
 144 #if defined(__cplusplus)
 145 }
 146 #endif
 147
 148 #endif