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      1 /*
      2  * Copyright (C) 2015 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 "event_fd.h"
     18 
     19 #include <fcntl.h>
     20 #include <poll.h>
     21 #include <stdio.h>
     22 #include <string.h>
     23 #include <sys/ioctl.h>
     24 #include <sys/mman.h>
     25 #include <sys/syscall.h>
     26 #include <sys/types.h>
     27 #include <atomic>
     28 #include <memory>
     29 
     30 #include <android-base/file.h>
     31 #include <android-base/logging.h>
     32 #include <android-base/stringprintf.h>
     33 
     34 #include "event_type.h"
     35 #include "perf_event.h"
     36 #include "utils.h"
     37 
     38 std::vector<char> EventFd::data_process_buffer_;
     39 
     40 static int perf_event_open(perf_event_attr* attr, pid_t pid, int cpu, int group_fd,
     41                            unsigned long flags) {
     42   return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
     43 }
     44 
     45 std::unique_ptr<EventFd> EventFd::OpenEventFile(const perf_event_attr& attr, pid_t tid, int cpu,
     46                                                 bool report_error) {
     47   perf_event_attr perf_attr = attr;
     48   std::string event_name = "unknown event";
     49   const EventType* event_type = FindEventTypeByConfig(perf_attr.type, perf_attr.config);
     50   if (event_type != nullptr) {
     51     event_name = event_type->name;
     52   }
     53   int perf_event_fd = perf_event_open(&perf_attr, tid, cpu, -1, 0);
     54   if (perf_event_fd == -1) {
     55     if (report_error) {
     56       PLOG(ERROR) << "open perf_event_file (event " << event_name << ", tid " << tid << ", cpu "
     57                   << cpu << ") failed";
     58     } else {
     59       PLOG(DEBUG) << "open perf_event_file (event " << event_name << ", tid " << tid << ", cpu "
     60                   << cpu << ") failed";
     61     }
     62     return nullptr;
     63   }
     64   if (fcntl(perf_event_fd, F_SETFD, FD_CLOEXEC) == -1) {
     65     if (report_error) {
     66       PLOG(ERROR) << "fcntl(FD_CLOEXEC) for perf_event_file (event " << event_name << ", tid "
     67                   << tid << ", cpu " << cpu << ") failed";
     68     } else {
     69       PLOG(DEBUG) << "fcntl(FD_CLOEXEC) for perf_event_file (event " << event_name << ", tid "
     70                   << tid << ", cpu " << cpu << ") failed";
     71     }
     72     return nullptr;
     73   }
     74   return std::unique_ptr<EventFd>(new EventFd(perf_event_fd, event_name, tid, cpu));
     75 }
     76 
     77 EventFd::~EventFd() {
     78   if (mmap_addr_ != nullptr) {
     79     munmap(mmap_addr_, mmap_len_);
     80   }
     81   close(perf_event_fd_);
     82 }
     83 
     84 std::string EventFd::Name() const {
     85   return android::base::StringPrintf("perf_event_file(event %s, tid %d, cpu %d)",
     86                                      event_name_.c_str(), tid_, cpu_);
     87 }
     88 
     89 uint64_t EventFd::Id() const {
     90   if (id_ == 0) {
     91     PerfCounter counter;
     92     if (ReadCounter(&counter)) {
     93       id_ = counter.id;
     94     }
     95   }
     96   return id_;
     97 }
     98 
     99 bool EventFd::ReadCounter(PerfCounter* counter) const {
    100   CHECK(counter != nullptr);
    101   if (!android::base::ReadFully(perf_event_fd_, counter, sizeof(*counter))) {
    102     PLOG(ERROR) << "ReadCounter from " << Name() << " failed";
    103     return false;
    104   }
    105   return true;
    106 }
    107 
    108 bool EventFd::MmapContent(size_t mmap_pages) {
    109   CHECK(IsPowerOfTwo(mmap_pages));
    110   size_t page_size = sysconf(_SC_PAGE_SIZE);
    111   size_t mmap_len = (mmap_pages + 1) * page_size;
    112   void* mmap_addr = mmap(nullptr, mmap_len, PROT_READ | PROT_WRITE, MAP_SHARED, perf_event_fd_, 0);
    113   if (mmap_addr == MAP_FAILED) {
    114     PLOG(ERROR) << "mmap() failed for " << Name();
    115     return false;
    116   }
    117   mmap_addr_ = mmap_addr;
    118   mmap_len_ = mmap_len;
    119   mmap_metadata_page_ = reinterpret_cast<perf_event_mmap_page*>(mmap_addr_);
    120   mmap_data_buffer_ = reinterpret_cast<char*>(mmap_addr_) + page_size;
    121   mmap_data_buffer_size_ = mmap_len_ - page_size;
    122   if (data_process_buffer_.size() < mmap_data_buffer_size_) {
    123     data_process_buffer_.resize(mmap_data_buffer_size_);
    124   }
    125   return true;
    126 }
    127 
    128 size_t EventFd::GetAvailableMmapData(char** pdata) {
    129   // The mmap_data_buffer is used as a ring buffer like below. The kernel continuously writes
    130   // records to the buffer, and the user continuously read records out.
    131   //         _________________________________________
    132   // buffer | can write   |   can read   |  can write |
    133   //                      ^              ^
    134   //                    read_head       write_head
    135   //
    136   // So the user can read records in [read_head, write_head), and the kernel can write records
    137   // in [write_head, read_head). The kernel is responsible for updating write_head, and the user
    138   // is responsible for updating read_head.
    139 
    140   size_t buf_mask = mmap_data_buffer_size_ - 1;
    141   size_t write_head = static_cast<size_t>(mmap_metadata_page_->data_head & buf_mask);
    142   size_t read_head = static_cast<size_t>(mmap_metadata_page_->data_tail & buf_mask);
    143 
    144   if (read_head == write_head) {
    145     // No available data.
    146     return 0;
    147   }
    148 
    149   // Make sure we can see the data after the fence.
    150   std::atomic_thread_fence(std::memory_order_acquire);
    151 
    152   // Copy records from mapped buffer to data_process_buffer. Note that records can be wrapped
    153   // at the end of the mapped buffer.
    154   char* to = data_process_buffer_.data();
    155   if (read_head < write_head) {
    156     char* from = mmap_data_buffer_ + read_head;
    157     size_t n = write_head - read_head;
    158     memcpy(to, from, n);
    159     to += n;
    160   } else {
    161     char* from = mmap_data_buffer_ + read_head;
    162     size_t n = mmap_data_buffer_size_ - read_head;
    163     memcpy(to, from, n);
    164     to += n;
    165     from = mmap_data_buffer_;
    166     n = write_head;
    167     memcpy(to, from, n);
    168     to += n;
    169   }
    170   size_t read_bytes = to - data_process_buffer_.data();
    171   *pdata = data_process_buffer_.data();
    172   DiscardMmapData(read_bytes);
    173   return read_bytes;
    174 }
    175 
    176 void EventFd::DiscardMmapData(size_t discard_size) {
    177   mmap_metadata_page_->data_tail += discard_size;
    178 }
    179 
    180 void EventFd::PreparePollForMmapData(pollfd* poll_fd) {
    181   memset(poll_fd, 0, sizeof(pollfd));
    182   poll_fd->fd = perf_event_fd_;
    183   poll_fd->events = POLLIN;
    184 }
    185 
    186 bool IsEventAttrSupportedByKernel(perf_event_attr attr) {
    187   auto event_fd = EventFd::OpenEventFile(attr, getpid(), -1, false);
    188   return event_fd != nullptr;
    189 }
    190