zircon/system/ulib/zxio/debuglog.cc

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/sync/mutex.h>
#include <lib/zxio/inception.h>
#include <lib/zxio/null.h>
#include <lib/zxio/ops.h>
#include <zircon/syscalls/log.h>

#include <array>

#include "private.h"

#define LOGBUF_MAX (ZX_LOG_RECORD_MAX - sizeof(zx_log_record_t))

namespace {

// A |zxio_t| backend that uses a debuglog.
//
// The |handle| handle is a Zircon debuglog object.
class Debuglog : public HasIo {
 public:
  explicit Debuglog(zx::debuglog debuglog) : HasIo(kOps), handle_(std::move(debuglog)) {}

 private:
  zx_status_t Close();
  zx_status_t Clone(zx_handle_t* out_handle);
  zx_status_t Writev(const zx_iovec_t* vector, size_t vector_count, zxio_flags_t flags,
                     size_t* out_actual);
  zx_status_t IsATty(bool* tty);

  static const zxio_ops_t kOps;

  zx::debuglog handle_;
  sync_mutex_t lock_;
  struct {
    unsigned next = 0;
    std::unique_ptr<std::array<char, LOGBUF_MAX>> pending;
  } buffer_ __TA_GUARDED(lock_);
};

constexpr zxio_ops_t Debuglog::kOps = ([]() {
  using Adaptor = Adaptor<Debuglog>;
  zxio_ops_t ops = zxio_default_ops;
  ops.close = Adaptor::From<&Debuglog::Close>;
  ops.clone = Adaptor::From<&Debuglog::Clone>;
  ops.writev = Adaptor::From<&Debuglog::Writev>;
  ops.isatty = Adaptor::From<&Debuglog::IsATty>;
  return ops;
})();

zx_status_t Debuglog::Close() {
  this->~Debuglog();
  return ZX_OK;
}

zx_status_t Debuglog::Clone(zx_handle_t* out_handle) {
  zx::debuglog handle;
  zx_status_t status = handle_.duplicate(ZX_RIGHT_SAME_RIGHTS, &handle);
  *out_handle = handle.release();
  return status;
}

zx_status_t Debuglog::Writev(const zx_iovec_t* vector, size_t vector_count, zxio_flags_t flags,
                             size_t* out_actual) {
  if (flags) {
    return ZX_ERR_NOT_SUPPORTED;
  }

  auto& outgoing = buffer_;
  sync_mutex_lock(&lock_);
  if (outgoing.pending == nullptr) {
    outgoing.pending = std::make_unique<std::array<char, LOGBUF_MAX>>();
  }

  zx_status_t status = zxio_do_vector(
      vector, vector_count, out_actual, [&](void* buffer, size_t capacity, size_t* out_actual) {
        // Convince the compiler that the lock is held here. This is safe
        // because the lock is held over the call to zxio_do_vector and
        // zxio_do_vector is synchronous, so it cannot extend the life of this
        // lambda.
        //
        // This is required because the compiler does its analysis
        // function-by-function. In this function, it can't see that the lock is
        // held by the calling scope. If We annotate this function with
        // TA_REQUIRES, then this function compiles, but its call in
        // zxio_do_vector doesn't, because the compiler can't tell that the lock
        // is held in that function.
        []() __TA_ASSERT(lock_) {}();
        const char* data = static_cast<const char*>(buffer);
        for (size_t i = 0; i < capacity; ++i) {
          char c = *data++;
          if (c == '\n') {
            handle_.write(0, outgoing.pending->data(), outgoing.next);
            outgoing.next = 0;
            continue;
          }
          if (c < ' ') {
            continue;
          }
          (*outgoing.pending)[outgoing.next++] = c;
          if (outgoing.next == LOGBUF_MAX) {
            handle_.write(0, outgoing.pending->data(), outgoing.next);
            outgoing.next = 0;
            continue;
          }
        }
        *out_actual = capacity;
        return ZX_OK;
      });
  sync_mutex_unlock(&lock_);
  return status;
}

zx_status_t Debuglog::IsATty(bool* tty) {
  // debuglog needs to be a tty in order to tell stdio
  // to use line-buffering semantics - bunching up log messages
  // for an arbitrary amount of time makes for confusing results!
  *tty = true;
  return ZX_OK;
}

}  // namespace

zx_status_t zxio_debuglog_init(zxio_storage_t* storage, zx::debuglog handle) {
  new (storage) Debuglog(std::move(handle));
  return ZX_OK;
}