将USB文件描述符传递给Android NDK程序

Question

我试图将用C编写的一些软件移植到Android平台.该软件具有可以从连接的USB设备读取和写入的组件.我想要做的是在Java中打开与设备的连接,然后将USB设备的文件描述符传递给JNI代码.

下面是lsof我的应用程序的(相关)输出,显示我有两个USB设备描述符:

com.tim    8861     u0_a66   35       ???                ???       ???        ??? /dev/bus/usb/001/002
com.tim    8861     u0_a66   36       ???                ???       ???        ??? socket:[51170]
com.tim    8861     u0_a66   37       ???                ???       ???        ??? socket:[51173]
com.tim    8861     u0_a66   38       ???                ???       ???        ??? /dev/bus/usb/001/003

我已将两个描述符(上面为35和38)传递给我的本机方法,但是当我尝试写入任一文件描述符时,write()返回-1,并且我收到EINVAL错误.

这是我的原生方法的主体:

char buff[1024] = {0};
jsize len = (*env)->GetArrayLength(env, fds);
jint *arr = (*env)->GetIntArrayElements(env, fds, 0);
int i;

char data[4] = {
    0x09,
    0x90,
    0x50,
    0x50,
};

for (i = 0; i < len; i++) {
    int wrote = write(arr[i], data, 4);

    int flags = fcntl(arr[i], F_GETFL);
    char *err = strerror(errno);
    sprintf(buff, "%sFD: %d  \n"
    "wrote: %d  \n"
    "(err: %d %s)  \n"
    "flags: %d  \n"
    "NBIO %d  \n"
    "readonly %d  \n"
    "writeonly %d  \n"
    "both %d  \n"
    "append %d  \n"
    "large file %d  \n\n", buff, arr[i], wrote, errno, err, flags, flags & O_NONBLOCK,
        flags & O_RDONLY, flags & O_WRONLY, flags & O_RDWR, flags & O_APPEND,
        flags & O_LARGEFILE);
}
return (*env)->NewStringUTF(env, buff);

调用该方法时返回的字符串是:

FD: 35  
wrote: -1  
(err: 22 Invalid argument)  
flags: 32770  
NBIO 0  
readonly 0  
writeonly 0  
both 2  
append 0  
large file 32768  

FD: 38  
wrote: -1  
(err: 22 Invalid argument)  
flags: 32770  
NBIO 0  
readonly 0  
writeonly 0  
both 2  
append 0  
large file 32768

写入USB设备确实可以通过Java工作,因此在尝试通过本机代码执行此操作时似乎只是一个问题.

有没有人有这样的经历呢？

Answer 1

似乎write()在USB文件描述符上使用并不完全有效,因为USB设备上有多个可以写入数据的端点.

我能够使用该ioctl()功能执行批量传输到设备上的特定端点:

#include <linux/usbdevice_fs.h>
#include <sys/ioctl.h>

// ...

char data[4] = {0x09, 0x90, 0x50, 0x50};

struct usbdevfs_bulktransfer bt;
bt.ep = usb_endpoint;  /* endpoint (received from Java) */
bt.len = 4;            /* length of data */
bt.timeout = 100;      /* timeout in ms */
bt.data = data;        /* the data */

int rtn = ioctl(fd, USBDEVFS_BULK, &bt);