diff --git a/libusbhost/usbhost.c b/libusbhost/usbhost.c index 44b878d2c..4d286bf9d 100644 --- a/libusbhost/usbhost.c +++ b/libusbhost/usbhost.c @@ -324,29 +324,39 @@ void usb_host_run(struct usb_host_context *context, 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; + } } - - if (fd < 0) - return NULL; - writeable = 0; - D("[ usb open read-only %s fd = %d]\n", dev_name, fd); + /* not writeable or readable - sleep and try again. */ + D("usb_device_open no access sleeping\n"); + usleep(SLEEP_BETWEEN_ATTEMPTS_US); } + 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) result->writeable = writeable;