Re: [PATCH] USB: add USB test and measurement class driver - round 2

Oliver Neukum
2008-08-28T10:09:28Z

Am Donnerstag 28 August 2008 01:47:20 schrieb Greg KH:
> On Wed, Aug 27, 2008 at 02:58:08PM -0400, Alan Stern wrote:
> > On Wed, 27 Aug 2008, Greg KH wrote:
> >
> > > On Wed, Aug 27, 2008 at 02:28:22PM -0400, Alan Stern wrote:
> > > > On Wed, 27 Aug 2008, Greg KH wrote:
> > > >
> > > > > Here's an updated version of the usbtmc driver, with all of the
> > > > > different issues that have been raised, hopefully addressed.
> > > >
> > > > This is an example of what I was discussing with Oliver. In all
> > > > likelihood you simply don't need usbtmc_mutex, and using it will cause
> > > > a lockdep violation.
> > > >
> > > > That's why so many of the other USB class drivers don't have an
> > > > analogous static mutex.
> > >
> > > Ok, then it's just safe to drop this static mutex entirely, right?
> >
> > Yes, once you add the call to usb_deregister_dev.
>
> Great, all done now.
>
> Here's the updated version.

OK, here we go again.

> +static ssize_t usbtmc_read(struct file *filp, char __user *buf,
> + size_t count, loff_t *f_pos)
> +{

[..]

> + /* Setup IO buffer for DEV_DEP_MSG_IN message
> + * Refer to class specs for details
> + */
> + buffer[0] = 2;
> + buffer[1] = data->bTag;
> + buffer[2] = ~(data->bTag);
> + buffer[3] = 0; /* Reserved */
> + buffer[4] = (this_part - 12 - 3) & 255;
> + buffer[5] = ((this_part - 12 - 3) >> 8) & 255;
> + buffer[6] = ((this_part - 12 - 3) >> 16) & 255;
> + buffer[7] = ((this_part - 12 - 3) >> 24) & 255;

We have excellent endianness conversion macros.

> + buffer[8] = data->TermCharEnabled * 2;
> + /* Use term character? */

smp_rmb(); /* we must make sure we don't read a stale terminator */

> + buffer[9] = data->TermChar;
> + buffer[10] = 0; /* Reserved */
> + buffer[11] = 0; /* Reserved */
> +
> + /* Send bulk URB */
> + retval = usb_bulk_msg(data->usb_dev,
> + usb_sndbulkpipe(data->usb_dev,
> + data->bulk_out),
> + buffer, 12, &actual, USBTMC_TIMEOUT);
> +
> + /* Store bTag (in case we need to abort) */
> + data->bTag_last_write = data->bTag;

even if usb_bulk_msg() failed?

> +
> + /* Increment bTag -- and increment again if zero */
> + data->bTag++;
> + if (!data->bTag)
> + (data->bTag)++;
> +
> + if (retval < 0) {
> + dev_err(dev, "usb_bulk_msg returned %d\n", retval);
> + if (data->auto_abort)
> + usbtmc_ioctl_abort_bulk_out(data);
> + goto exit;
> + }
> +
> + /* Send bulk URB */
> + retval = usb_bulk_msg(data->usb_dev,
> + usb_rcvbulkpipe(data->usb_dev,
> + data->bulk_in),
> + buffer, USBTMC_SIZE_IOBUFFER, &actual,
> + USBTMC_TIMEOUT);
> +
> + /* Store bTag (in case we need to abort) */
> + data->bTag_last_read = data->bTag;
> +
> + if (retval < 0) {
> + dev_err(dev, "Unable to read data, error %d\n", retval);
> + if (data->auto_abort)
> + usbtmc_ioctl_abort_bulk_in(data);
> + goto exit;
> + }
> +
> + /* How many characters did the instrument send? */
> + n_characters = buffer[4] +
> + (buffer[5] << 8) +
> + (buffer[6] << 16) +
> + (buffer[7] << 24);

endianness macro

> +
> + /* Copy buffer to user space */
> + if (copy_to_user(buf + done, &buffer[12], n_characters)) {
> + /* There must have been an addressing problem */
> + retval = -EFAULT;
> + goto exit;
> + }
> +
> + done += n_characters;
> + if (n_characters < USBTMC_SIZE_IOBUFFER)
> + remaining = 0;
> + }
> +
> + /* Update file position value */
> + *f_pos = *f_pos + done;

That'll get out of sync if -EFAULT is returned

> + retval = done;
> +
> +exit:
> + mutex_unlock(&data->io_mutex);
> + kfree(buffer);
> + return retval;
> +}
> +
> +static ssize_t usbtmc_write(struct file *filp, const char __user *buf,
> + size_t count, loff_t *f_pos)
> +{
> + struct usbtmc_device_data *data;
> + u8 *buffer;
> + int retval;
> + int actual;
> + unsigned long int n_bytes;
> + int n;
> + int remaining;
> + int done;
> + int this_part;
> +
> + data = filp->private_data;
> +
> + buffer = kmalloc(USBTMC_SIZE_IOBUFFER, GFP_KERNEL);
> + if (!buffer)
> + return -ENOMEM;
> +
> + mutex_lock(&data->io_mutex);

This and usbtmc_read() need a test for disconnection. Open() and disconnect
are guarded in usbcore, read & write are not. By reference count you've made
sure you have a valid device descriptor, but the device may have been reprobed.

> +
> + remaining = count;
> + done = 0;
> +
> + while (remaining > 0) {
> + if (remaining > USBTMC_SIZE_IOBUFFER - 12) {
> + this_part = USBTMC_SIZE_IOBUFFER - 12;
> + buffer[8] = 0;
> + } else {
> + this_part = remaining;
> + buffer[8] = 1;
> + }
> +
> + /* Setup IO buffer for DEV_DEP_MSG_OUT message */
> + buffer[0] = 1;
> + buffer[1] = data->bTag;
> + buffer[2] = ~(data->bTag);
> + buffer[3] = 0; /* Reserved */
> + buffer[4] = this_part & 255;
> + buffer[5] = (this_part >> 8) & 255;
> + buffer[6] = (this_part >> 16) & 255;
> + buffer[7] = (this_part >> 24) & 255;

endianness macro

> + /* buffer[8] is set above... */
> + buffer[9] = 0; /* Reserved */
> + buffer[10] = 0; /* Reserved */
> + buffer[11] = 0; /* Reserved */
> +
> + if (copy_from_user(&buffer[12], buf + done, this_part)) {
> + retval = -EFAULT;
> + goto exit;
> + }
> +
> + n_bytes = 12 + this_part;
> + if (this_part % 4)
> + n_bytes += 4 - this_part % 4;
> + for (n = 12 + this_part; n < n_bytes; n++)
> + buffer[n] = 0;
> +
> + retval = usb_bulk_msg(data->usb_dev,
> + usb_sndbulkpipe(data->usb_dev,
> + data->bulk_out),
> + buffer, n_bytes, &actual, USBTMC_TIMEOUT);
> +
> + data->bTag_last_write = data->bTag;

error case?

[..]
> +static int get_capabilities(struct usbtmc_device_data *data)
> +{
> + struct device *dev = &data->usb_dev->dev;
> + char *buffer;
> + int rv;
> +
> + buffer = kmalloc(0x18, GFP_KERNEL);
> + if (!buffer)
> + return -ENOMEM;
> +
> + rv = usb_control_msg(data->usb_dev, usb_rcvctrlpipe(data->usb_dev, 0),
> + USBTMC_REQUEST_GET_CAPABILITIES,
> + USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
> + 0, 0, buffer, 0x18, USBTMC_TIMEOUT);
> + if (rv < 0) {
> + dev_err(dev, "usb_control_msg returned %d\n", rv);
> + return rv;

memory leak

> + }
> +
> + dev_dbg(dev, "GET_CAPABILITIES returned %x\n", buffer[0]);
> + dev_dbg(dev, "Interface capabilities are %x\n", buffer[4]);
> + dev_dbg(dev, "Device capabilities are %x\n", buffer[5]);
> + dev_dbg(dev, "USB488 interface capabilities are %x\n", buffer[14]);
> + dev_dbg(dev, "USB488 device capabilities are %x\n", buffer[15]);
> + if (buffer[0] != USBTMC_STATUS_SUCCESS) {
> + dev_err(dev, "GET_CAPABILITIES returned %x\n", buffer[0]);
> + return -EPERM;

memory leak

[..]
> +static ssize_t store_TermChar(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct usb_interface *intf = to_usb_interface(dev);
> + struct usbtmc_device_data *data = usb_get_intfdata(intf);
> +
> + if (count < 1)
> + return -EINVAL;
> + data->TermChar = buf[0];

smp_wmb(); /* must hit RAM before enablement */

> + return count;
> +}
> +static DEVICE_ATTR(TermChar, S_IRUGO, show_TermChar, store_TermChar);
> +
> +#define data_attribute(name) \
> +static ssize_t show_##name(struct device *dev, \
> + struct device_attribute *attr, char *buf) \
> +{ \
> + struct usb_interface *intf = to_usb_interface(dev); \
> + struct usbtmc_device_data *data = usb_get_intfdata(intf); \
> + \
> + return sprintf(buf, "%d\n", data->name); \
> +} \
> +static ssize_t store_##name(struct device *dev, \
> + struct device_attribute *attr, \
> + const char *buf, size_t count) \
> +{ \
> + struct usb_interface *intf = to_usb_interface(dev); \
> + struct usbtmc_device_data *data = usb_get_intfdata(intf); \
> + ssize_t result; \
> + unsigned val; \
> + \
> + result = sscanf(buf, "%u\n", &val); \
> + if (result != 1) \
> + result = -EINVAL; \

smp_rmb(); /* must hit RAM after the terminator */ \

There are subtle penalties to avoiding ioctl(). Among them is the loss
of atomicity.
[..]
> +static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> + struct usbtmc_device_data *data;
> + int retval = -EBADRQC;
> +
> + data = file->private_data;
> + mutex_lock(&data->io_mutex);

check for disconnect as in read & write

> +
> + switch (cmd) {
> + case USBTMC_IOCTL_CLEAR_OUT_HALT:
> + retval = usbtmc_ioctl_clear_out_halt(data);
> +
> + case USBTMC_IOCTL_CLEAR_IN_HALT:
> + retval = usbtmc_ioctl_clear_in_halt(data);
> +
> + case USBTMC_IOCTL_INDICATOR_PULSE:
> + retval = usbtmc_ioctl_indicator_pulse(data);
> +
> + case USBTMC_IOCTL_CLEAR:
> + retval = usbtmc_ioctl_clear(data);
> +
> + case USBTMC_IOCTL_ABORT_BULK_OUT:
> + retval = usbtmc_ioctl_abort_bulk_out(data);
> +
> + case USBTMC_IOCTL_ABORT_BULK_IN:
> + retval = usbtmc_ioctl_abort_bulk_in(data);
> + }

This is missing a whole lot of "break;"

> +static int usbtmc_probe(struct usb_interface *intf,
> + const struct usb_device_id *id)
> +{
> + struct usbtmc_device_data *data;
> + struct usb_host_interface *iface_desc;
> + struct usb_endpoint_descriptor *endpoint;
> + int n;
> + int retcode;
> +
> + dev_dbg(&intf->dev, "%s called\n", __func__);
> +
> + data = kmalloc(sizeof(struct usbtmc_device_data), GFP_KERNEL);
> + if (!data) {
> + dev_err(&intf->dev, "Unable to allocate kernel memory\n");
> + return -ENOMEM;
> + }
> +
> + data->intf = intf;
> + data->id = id;
> + data->usb_dev = usb_get_dev(interface_to_usbdev(intf));
> + usb_set_intfdata(intf, data);
> + kref_init(&data->kref);
> + mutex_init(&data->io_mutex);
> +
> + /* Initialize USBTMC bTag and other fields */
> + data->bTag = 1;
> + data->TermCharEnabled = 0;
> + data->TermChar = '\n';
> +
> + /* USBTMC devices have only one setting, so use that */
> + iface_desc = data->intf->cur_altsetting;
> +
> + /* Find bulk in endpoint */
> + for (n = 0; n < iface_desc->desc.bNumEndpoints; n++) {
> + endpoint = &iface_desc->endpoint[n].desc;
> +
> + if (usb_endpoint_is_bulk_in(endpoint)) {
> + data->bulk_in = endpoint->bEndpointAddress;
> + dev_dbg(&intf->dev, "Found bulk in endpoint at %u\n",
> + data->bulk_in);
> + break;
> + }
> + }
> +
> + /* Find bulk out endpoint */
> + for (n = 0; n < iface_desc->desc.bNumEndpoints; n++) {
> + endpoint = &iface_desc->endpoint[n].desc;
> +
> + if (usb_endpoint_is_bulk_out(endpoint)) {
> + data->bulk_out = endpoint->bEndpointAddress;
> + dev_dbg(&intf->dev, "Found Bulk out endpoint at %u\n",
> + data->bulk_out);
> + break;
> + }
> + }
> +
> + retcode = get_capabilities(data);
> + if (retcode)
> + dev_err(&intf->dev, "can't read capabilities\n");
> + else
> + retcode = sysfs_create_group(&intf->dev.kobj,
> + &capability_attr_grp);
> +
> + retcode = sysfs_create_group(&intf->dev.kobj, &data_attr_grp);

If you ignore an error return, be open about it.

> + retcode = usb_register_dev(intf, &usbtmc_class);
> + if (retcode) {
> + dev_err(&intf->dev, "Not able to get a minor"
> + " (base %u, slice default): %d\n", USBTMC_MINOR_BASE,
> + retcode);
> + goto error_register;
> + }
> + dev_dbg(&intf->dev, "Using minor number %d\n", intf->minor);
> +
> + return 0;
> +
> +error_register:
> + sysfs_remove_group(&intf->dev.kobj, &capability_attr_grp);
> + sysfs_remove_group(&intf->dev.kobj, &data_attr_grp);

The groups might never have been created.

> + kref_put(&data->kref, usbtmc_delete);
> + return retcode;
> +}
> +
> +static void usbtmc_disconnect(struct usb_interface *intf)
> +{
> + struct usbtmc_device_data *data;
> +
> + dev_dbg(&intf->dev, "usbtmc_disconnect called\n");
> +

You must set a flag for read, write and ioctl.

Regards
Oliver