Merge "usblib: fix race & delay waiting for perms on open"

struct usb_device *usb_device_open(const char *dev_name)

{

    int fd, did_retry = 0, writeable = 1;

    int fd, attempts, writeable = 1;

    const int SLEEP_BETWEEN_ATTEMPTS_US = 100000; /* 100 ms */

    const int64_t MAX_ATTEMPTS = 10;              /* 1s */

    D("usb_device_open %s\n", dev_name);

retry:

    fd = open(dev_name, O_RDWR);

    if (fd < 0) {

        /* if we fail, see if have read-only access */

        fd = open(dev_name, O_RDONLY);

        D("usb_device_open open returned %d errno %d\n", fd, errno);

        if (fd < 0 && (errno == EACCES || errno == ENOENT) && !did_retry) {

            /* work around race condition between inotify and permissions management */

            sleep(1);

            did_retry = 1;

            goto retry;

    /* Hack around waiting for permissions to be set on the USB device node.

     * Should really be a timeout instead of attempt count, and should REALLY

     * be triggered by the perm change via inotify rather than polling.

     */

    for (attempts = 0; attempts < MAX_ATTEMPTS; ++attempts) {

        if (access(dev_name, R_OK | W_OK) == 0) {

            writeable = 1;

            break;

        } else {

            if (access(dev_name, R_OK) == 0) {

                /* double check that write permission didn't just come along too! */

                writeable = (access(dev_name, R_OK | W_OK) == 0);

                break;

            }

        }

        /* not writeable or readable - sleep and try again. */

        D("usb_device_open no access sleeping\n");

        usleep(SLEEP_BETWEEN_ATTEMPTS_US);

    }

        if (fd < 0)

            return NULL;

        writeable = 0;

        D("[ usb open read-only %s fd = %d]\n", dev_name, fd);

    if (writeable) {

        fd = open(dev_name, O_RDWR);

    } else {

        fd = open(dev_name, O_RDONLY);

    }

    D("usb_device_open open returned %d writeable %d errno %d\n", fd, writeable, errno);

    if (fd < 0) return NULL;

    struct usb_device* result = usb_device_new(dev_name, fd);

    if (result)