linux ioctl的使用

一、ioctl是什么？

ioctl操作与硬件平台操作息息相关.
#include
int ioctl(fd,unsigned long cmd,...);
if(ret>0)
{
   
  perror("ioctl failure\n");
}
//include/uapi/sound/asound.h
#define VFAT_IOCTL_READDIR_BOTH  _IOR(r,1,struct __fat_dirent[2])
#define SNDRV_PCM_IOCTL_PVERSION	_IOR('A', 0x00, int)
#define SNDRV_PCM_IOCTL_INFO		_IOR('A', 0x01, struct snd_pcm_info)
#define SNDRV_PCM_IOCTL_TSTAMP		_IOW('A', 0x02, int)
#define SNDRV_PCM_IOCTL_TTSTAMP		_IOW('A', 0x03, int)
#define SNDRV_PCM_IOCTL_USER_PVERSION	_IOW('A', 0x04, int)
#define SNDRV_PCM_IOCTL_HW_REFINE	_IOWR('A', 0x10, struct snd_pcm_hw_params)
#define SNDRV_PCM_IOCTL_HW_PARAMS	_IOWR('A', 0x11, struct snd_pcm_hw_params)
#define SNDRV_PCM_IOCTL_HW_FREE		_IO('A', 0x12)
#define SNDRV_PCM_IOCTL_SW_PARAMS	_IOWR('A', 0x13, struct snd_pcm_sw_params)
#define SNDRV_PCM_IOCTL_STATUS		_IOR('A', 0x20, struct snd_pcm_status)
#define SNDRV_PCM_IOCTL_DELAY		_IOR('A', 0x21, snd_pcm_sframes_t)
#define SNDRV_PCM_IOCTL_HWSYNC		_IO('A', 0x22)
#define SNDRV_PCM_IOCTL_SYNC_PTR	_IOWR('A', 0x23, struct snd_pcm_sync_ptr)
#define SNDRV_PCM_IOCTL_STATUS_EXT	_IOWR('A', 0x24, struct snd_pcm_status)
#define SNDRV_PCM_IOCTL_CHANNEL_INFO	_IOR('A', 0x32, struct snd_pcm_channel_info)
#define SNDRV_PCM_IOCTL_PREPARE		_IO('A', 0x40)
#define SNDRV_PCM_IOCTL_RESET		_IO('A', 
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