third-party/folly/src/folly/detail/FileUtilDetail.h

   1 /*
   2  * Copyright (c) Meta Platforms, Inc. and affiliates.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #pragma once
  18
  19 #include <cerrno>
  20 #include <cstddef>
  21 #include <type_traits>
  22
  23 #include <folly/portability/SysTypes.h>
  24
  25 //  Private functions for wrapping file-io against interrupt and partial op
  26 //  completions.
  27 //
  28 //  This header is intended to be extremely lightweight. In particular, the
  29 //  parallel private functions for wrapping vector file-io are in a separate
  30 //  header.
  31
  32 namespace folly {
  33 namespace fileutil_detail {
  34
  35 // Wrap call to f(args) in loop to retry on EINTR
  36 template <class F, class... Args>
  37 ssize_t wrapNoInt(F f, Args... args) {
  38   ssize_t r;
  39   do {
  40     r = f(args...);
  41   } while (r == -1 && errno == EINTR);
  42   return r;
  43 }
  44
  45 inline void incr(ssize_t) {}
  46 template <typename Offset>
  47 inline void incr(ssize_t n, Offset& offset) {
  48   offset += static_cast<Offset>(n);
  49 }
  50
  51 // Wrap call to read/pread/write/pwrite(fd, buf, count, offset?) to retry on
  52 // incomplete reads / writes.  The variadic argument magic is there to support
  53 // an additional argument (offset) for pread / pwrite; see the incr() functions
  54 // above which do nothing if the offset is not present and increment it if it
  55 // is.
  56 template <class F, class... Offset>
  57 ssize_t wrapFull(F f, int fd, void* buf, size_t count, Offset... offset) {
  58   char* b = static_cast<char*>(buf);
  59   ssize_t totalBytes = 0;
  60   ssize_t r;
  61   do {
  62     r = f(fd, b, count, offset...);
  63     if (r == -1) {
  64       if (errno == EINTR) {
  65         continue;
  66       }
  67       return r;
  68     }
  69
  70     totalBytes += r;
  71     b += r;
  72     count -= r;
  73     incr(r, offset...);
  74   } while (r != 0 && count); // 0 means EOF
  75
  76   return totalBytes;
  77 }
  78
  79 } // namespace fileutil_detail
  80 } // namespace folly