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SubjectRe: [PATCH 08/11] usb: Add USB subsystem notifications [ver #7]
On Fri, Aug 30, 2019 at 02:58:23PM +0100, David Howells wrote:
> Add a USB subsystem notification mechanism whereby notifications about
> hardware events such as device connection, disconnection, reset and I/O
> errors, can be reported to a monitoring process asynchronously.
>
> Firstly, an event queue needs to be created:
>
> fd = open("/dev/event_queue", O_RDWR);
> ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);
>
> then a notification can be set up to report USB notifications via that
> queue:
>
> struct watch_notification_filter filter = {
> .nr_filters = 1,
> .filters = {
> [0] = {
> .type = WATCH_TYPE_USB_NOTIFY,
> .subtype_filter[0] = UINT_MAX;
> },
> },
> };
> ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
> notify_devices(fd, 12);
>
> After that, records will be placed into the queue when events occur on a
> USB device or bus. Records are of the following format:
>
> struct usb_notification {
> struct watch_notification watch;
> __u32 error;
> __u32 reserved;
> __u8 name_len;
> __u8 name[0];
> } *n;
>
> Where:
>
> n->watch.type will be WATCH_TYPE_USB_NOTIFY
>
> n->watch.subtype will be the type of notification, such as
> NOTIFY_USB_DEVICE_ADD.
>
> n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
> record.
>
> n->watch.info & WATCH_INFO_ID will be the second argument to
> device_notify(), shifted.
>
> n->error and n->reserved are intended to convey information such as
> error codes, but are currently not used
>
> n->name_len and n->name convey the USB device name as an
> unterminated string. This may be truncated - it is currently
> limited to a maximum 63 chars.
>
> Note that it is permissible for event records to be of variable length -
> or, at least, the length may be dependent on the subtype.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> cc: linux-usb@vger.kernel.org
> ---
>
> Documentation/watch_queue.rst | 9 ++++++
> drivers/usb/core/Kconfig | 9 ++++++
> drivers/usb/core/devio.c | 56 ++++++++++++++++++++++++++++++++++++++
> drivers/usb/core/hub.c | 4 +++
> include/linux/usb.h | 18 ++++++++++++
> include/uapi/linux/watch_queue.h | 30 ++++++++++++++++++++
> 6 files changed, 125 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
> index 5cc9c6924727..4087a8e670a8 100644
> --- a/Documentation/watch_queue.rst
> +++ b/Documentation/watch_queue.rst
> @@ -11,6 +11,8 @@ receive notifications from the kernel. This can be used in conjunction with::
>
> * Block layer event notifications
>
> + * USB subsystem event notifications
> +
>
> The notifications buffers can be enabled by:
>
> @@ -315,6 +317,13 @@ Any particular buffer can be fed from multiple sources. Sources include:
> or temporary link loss. Watches of this type are set on the global device
> watch list.
>
> + * WATCH_TYPE_USB_NOTIFY
> +
> + Notifications of this type indicate USB subsystem events, such as
> + attachment, removal, reset and I/O errors. Separate events are generated
> + for buses and devices. Watchpoints of this type are set on the global
> + device watch list.
> +
>
> Event Filtering
> ===============
> diff --git a/drivers/usb/core/Kconfig b/drivers/usb/core/Kconfig
> index ecaacc8ed311..57e7b649e48b 100644
> --- a/drivers/usb/core/Kconfig
> +++ b/drivers/usb/core/Kconfig
> @@ -102,3 +102,12 @@ config USB_AUTOSUSPEND_DELAY
> The default value Linux has always had is 2 seconds. Change
> this value if you want a different delay and cannot modify
> the command line or module parameter.
> +
> +config USB_NOTIFICATIONS
> + bool "Provide USB hardware event notifications"
> + depends on USB && DEVICE_NOTIFICATIONS
> + help
> + This option provides support for getting hardware event notifications
> + on USB devices and interfaces. This makes use of the
> + /dev/watch_queue misc device to handle the notification buffer.
> + device_notify(2) is used to set/remove watches.
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index 9063ede411ae..b8572e4d6a1b 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -41,6 +41,7 @@
> #include <linux/dma-mapping.h>
> #include <asm/byteorder.h>
> #include <linux/moduleparam.h>
> +#include <linux/watch_queue.h>
>
> #include "usb.h"
>
> @@ -2660,13 +2661,68 @@ static void usbdev_remove(struct usb_device *udev)
> }
> }
>
> +#ifdef CONFIG_USB_NOTIFICATIONS
> +static noinline void post_usb_notification(const char *devname,
> + enum usb_notification_type subtype,
> + u32 error)
> +{
> + unsigned int gran = WATCH_LENGTH_GRANULARITY;
> + unsigned int name_len, n_len;
> + u64 id = 0; /* Might want to put a dev# here. */
> +
> + struct {
> + struct usb_notification n;
> + char more_name[USB_NOTIFICATION_MAX_NAME_LEN -
> + (sizeof(struct usb_notification) -
> + offsetof(struct usb_notification, name))];
> + } n;
> +
> + name_len = strlen(devname);
> + name_len = min_t(size_t, name_len, USB_NOTIFICATION_MAX_NAME_LEN);
> + n_len = round_up(offsetof(struct usb_notification, name) + name_len,
> + gran) / gran;
> +
> + memset(&n, 0, sizeof(n));
> + memcpy(n.n.name, devname, n_len);
> +
> + n.n.watch.type = WATCH_TYPE_USB_NOTIFY;
> + n.n.watch.subtype = subtype;
> + n.n.watch.info = n_len;
> + n.n.error = error;
> + n.n.name_len = name_len;
> +
> + post_device_notification(&n.n.watch, id);
> +}
> +
> +void post_usb_device_notification(const struct usb_device *udev,
> + enum usb_notification_type subtype, u32 error)
> +{
> + post_usb_notification(dev_name(&udev->dev), subtype, error);
> +}
> +
> +void post_usb_bus_notification(const struct usb_bus *ubus,
> + enum usb_notification_type subtype, u32 error)
> +{
> + post_usb_notification(ubus->bus_name, subtype, error);
> +}
> +#endif
> +
> static int usbdev_notify(struct notifier_block *self,
> unsigned long action, void *dev)
> {
> switch (action) {
> case USB_DEVICE_ADD:
> + post_usb_device_notification(dev, NOTIFY_USB_DEVICE_ADD, 0);
> break;
> case USB_DEVICE_REMOVE:
> + post_usb_device_notification(dev, NOTIFY_USB_DEVICE_REMOVE, 0);
> + usbdev_remove(dev);
> + break;
> + case USB_BUS_ADD:
> + post_usb_bus_notification(dev, NOTIFY_USB_BUS_ADD, 0);
> + break;
> + case USB_BUS_REMOVE:
> + post_usb_bus_notification(dev, NOTIFY_USB_BUS_REMOVE, 0);
> usbdev_remove(dev);

This added call to usbdev_remove() results in a crash when running
the qemu "tosa" emulation. Removing the call fixes the problem.

Guenter

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