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      1 //
      2 // Copyright (C) 2017 The Android Open Source Project
      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 #include "update_engine/payload_consumer/cached_file_descriptor.h"
     18 
     19 #include <unistd.h>
     20 
     21 #include <algorithm>
     22 
     23 #include <base/logging.h>
     24 
     25 #include "update_engine/common/utils.h"
     26 
     27 namespace chromeos_update_engine {
     28 
     29 off64_t CachedFileDescriptor::Seek(off64_t offset, int whence) {
     30   // Only support SEEK_SET and SEEK_CUR. I think these two would be enough. If
     31   // we want to support SEEK_END then we have to figure out the size of the
     32   // underlying file descriptor each time and it may not be a very good idea.
     33   CHECK(whence == SEEK_SET || whence == SEEK_CUR);
     34   off64_t next_offset = whence == SEEK_SET ? offset : offset_ + offset;
     35 
     36   if (next_offset != offset_) {
     37     // We sought somewhere other than what we are now. So we have to flush and
     38     // move to the new offset.
     39     if (!FlushCache()) {
     40       return -1;
     41     }
     42     // Then we have to seek there.
     43     if (fd_->Seek(next_offset, SEEK_SET) < 0) {
     44       return -1;
     45     }
     46     offset_ = next_offset;
     47   }
     48   return offset_;
     49 }
     50 
     51 ssize_t CachedFileDescriptor::Write(const void* buf, size_t count) {
     52   auto bytes = static_cast<const uint8_t*>(buf);
     53   size_t total_bytes_wrote = 0;
     54   while (total_bytes_wrote < count) {
     55     auto bytes_to_cache =
     56         std::min(count - total_bytes_wrote, cache_.size() - bytes_cached_);
     57     if (bytes_to_cache > 0) {  // Which means |cache_| is still have some space.
     58       memcpy(cache_.data() + bytes_cached_,
     59              bytes + total_bytes_wrote,
     60              bytes_to_cache);
     61       total_bytes_wrote += bytes_to_cache;
     62       bytes_cached_ += bytes_to_cache;
     63     }
     64     if (bytes_cached_ == cache_.size()) {
     65       // Cache is full; write it to the |fd_| as long as you can.
     66       if (!FlushCache()) {
     67         return -1;
     68       }
     69     }
     70   }
     71   offset_ += total_bytes_wrote;
     72   return total_bytes_wrote;
     73 }
     74 
     75 bool CachedFileDescriptor::Flush() {
     76   return FlushCache() && fd_->Flush();
     77 }
     78 
     79 bool CachedFileDescriptor::Close() {
     80   offset_ = 0;
     81   return FlushCache() && fd_->Close();
     82 }
     83 
     84 bool CachedFileDescriptor::FlushCache() {
     85   size_t begin = 0;
     86   while (begin < bytes_cached_) {
     87     auto bytes_wrote = fd_->Write(cache_.data() + begin, bytes_cached_ - begin);
     88     if (bytes_wrote < 0) {
     89       PLOG(ERROR) << "Failed to flush cached data!";
     90       return false;
     91     }
     92     begin += bytes_wrote;
     93   }
     94   bytes_cached_ = 0;
     95   return true;
     96 }
     97 
     98 }  // namespace chromeos_update_engine
     99