在Snap巨龙飞行DSP上打开的文件，返回可疑的大数字

Question

为什么，当调用open("/dev/tty-2",O_RDWR);时，打开的文件号是268435355 (例如-1+2^28)？这是一个在实时操作系统(比如android端)上从open()调用输出的正常大小的数字吗？好像太大了。

DSP处理器运行高通实时操作系统.其他运行Linaro的处理器。

mini-dm，DSP (数字信号处理器)运行时调试器的相关输出：

Running mini-dm version: 3.0
Device found with Product ID 0x9025. Continuing...
mini-dm is waiting for a DMSS connection...
DMSS is connected. Running mini-dm...
[08500/03]  00:40.640  HAP:63:HAP_debug_v2 weak ref not found, return _rtld_sym_zero@_rtld_objmain  0294  symbol.c
[08500/03]  00:40.640  HAP:63:HAP_debug_v2 weak ref not found, return _rtld_sym_zero@_rtld_objmain  0294  symbol.c
[08500/02]  00:40.640  HAP:63:Opening serial port  0062  helloworld_dsp.c
[08500/00]  00:40.640  configuring UART for 4-wire mode, DAL id: 0x2001005  0852  DalUart.c
[08500/02]  00:40.641  HAP:63:Opened serial port number 268435455  0065  helloworld_dsp.c
[08500/02]  00:40.641  HAP:63:Closing serial port  0075  helloworld_dsp.c
[08500/02]  00:40.641  HAP:63:Successfully closed serial port number 268435455  0078  helloworld_dsp.c
[08500/02]  00:40.641  HAP:63:Opening serial port  0062  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:workaround: reopening an existing serial port  0351  serial.c
[08500/02]  00:40.642  HAP:63:Opened serial port number 268435455  0065  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:Beginning serial read  0123  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:/dev/tty-2 read bytes [0]:   0129  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:Closing serial port  0075  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:Successfully closed serial port number 268435455  0078  helloworld_dsp.c

相关DSP代码：

int example_interface_serial_open()
{
LOG_INFO("Opening serial port");
  serial_fds[0] = open(serial_path[0],O_RDWR);
  if (serial_fds[0] >= SUCCESS) {
    LOG_INFO("Opened serial port number %d", serial_fds[0]);
  } else {
  //FIXME log error!
LOG_INFO("Error opening serial port");
    serial_fds[0] = ERROR;
  }
  return serial_fds[0];
}

int example_interface_serial_close(int fd) {
LOG_INFO("Closing serial port");

  if (!close(fd)) {
    LOG_INFO("Successfully closed serial port number %d", fd);
  } else {
    LOG_INFO("Error closing serial port");
    fd = ERROR;
  }

  return fd;
}

int example_interface_serial_read(int fd) {
  int res = SUCCESS;
  char rx_buffer[SERIAL_SIZE_OF_DATA_BUFFER];
  unsigned int num_bytes_read;
  int active_devices = 0;
  int runs, i;

  LOG_INFO("Beginning serial read");

  memset(rx_buffer, 0, SERIAL_SIZE_OF_DATA_BUFFER);
  num_bytes_read = read(fd, rx_buffer,
      SERIAL_SIZE_OF_DATA_BUFFER);
  LOG_INFO("%s read bytes [%d]: %s",
      serial_path[0], num_bytes_read, rx_buffer);

  if (res < SUCCESS) {
    LOG_INFO("Closing file %s",
      serial_path[0]);
    close(fd);
    fd = ERROR;
  }

return fd;
}

编辑:包括LOG_INFO()的定义

/****************************************************************************
 * Copyright (C) 2015 Mark Charlebois. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name ATLFlight nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/
#pragma once

#ifdef __cplusplus
extern "C" {
#endif

#ifdef __hexagon__
// Debug output on the aDSP
#include <HAP_farf.h>

#define LOG_INFO(...) FARF(ALWAYS, __VA_ARGS__);
#define LOG_ERR(...) FARF(ALWAYS, __VA_ARGS__);
#define LOG_DEBUG(...) FARF(MEDIUM, __VA_ARGS__);

#else
// Debug output on the apps processor
#include <stdio.h>
#define LOG_INFO(...) do{ printf(__VA_ARGS__); printf("\n"); } while (0)
#define LOG_ERR(...) do{ printf(__VA_ARGS__); printf("\n"); } while (0)
#define LOG_DEBUG(...) do{ printf(__VA_ARGS__); printf("\n"); } while (0)

#endif

#ifdef __cplusplus
}
#endif

int i=-1; LOG_INFO("%d\n",1);输出

DSP端：[08500/02] 02:27.822 HAP:24639: -1 0063 helloworld_dsp.c

Linux端：-1

Answer 1

设备的开发人员：

open()函数的返回值是一个有符号的int，成功的返回值是>= 0，失败的返回值小于零。 返回值如此大的原因是因为它被一个已知的常数0x0FFFFFFF所抵消。这样做是为了区分设备句柄和文件系统句柄(文件系统句柄总是小于0x0FFFFFF)，这些句柄在aDSP代码中处理不同。

古怪！:P