netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 139 insertions, 0 deletions

diff --git a/drivers/comedi/comedi_usb.c b/drivers/comedi/comedi_usb.c
new file mode 100644
index 000000000..75d65171c
--- /dev/null
+++ b/drivers/comedi/comedi_usb.c
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * comedi_usb.c
+ * Comedi USB driver specific functions.
+ *
+ * COMEDI - Linux Control and Measurement Device Interface
+ * Copyright (C) 1997-2000 David A. Schleef <ds@schleef.org>
+ */
+
+#include <linux/module.h>
+#include <linux/comedi/comedi_usb.h>
+
+/**
+ * comedi_to_usb_interface() - Return USB interface attached to COMEDI device
+ * @dev: COMEDI device.
+ *
+ * Assuming @dev->hw_dev is non-%NULL, it is assumed to be pointing to a
+ * a &struct device embedded in a &struct usb_interface.
+ *
+ * Return: Attached USB interface if @dev->hw_dev is non-%NULL.
+ * Return %NULL if @dev->hw_dev is %NULL.
+ */
+struct usb_interface *comedi_to_usb_interface(struct comedi_device *dev)
+{
+	return dev->hw_dev ? to_usb_interface(dev->hw_dev) : NULL;
+}
+EXPORT_SYMBOL_GPL(comedi_to_usb_interface);
+
+/**
+ * comedi_to_usb_dev() - Return USB device attached to COMEDI device
+ * @dev: COMEDI device.
+ *
+ * Assuming @dev->hw_dev is non-%NULL, it is assumed to be pointing to a
+ * a &struct device embedded in a &struct usb_interface.
+ *
+ * Return: USB device to which the USB interface belongs if @dev->hw_dev is
+ * non-%NULL.  Return %NULL if @dev->hw_dev is %NULL.
+ */
+struct usb_device *comedi_to_usb_dev(struct comedi_device *dev)
+{
+	struct usb_interface *intf = comedi_to_usb_interface(dev);
+
+	return intf ? interface_to_usbdev(intf) : NULL;
+}
+EXPORT_SYMBOL_GPL(comedi_to_usb_dev);
+
+/**
+ * comedi_usb_auto_config() - Configure/probe a USB COMEDI driver
+ * @intf: USB interface.
+ * @driver: Registered COMEDI driver.
+ * @context: Driver specific data, passed to comedi_auto_config().
+ *
+ * Typically called from the usb_driver (*probe) function.  Auto-configure a
+ * COMEDI device, using a pointer to the &struct device embedded in *@intf as
+ * the hardware device.  The @context value gets passed through to @driver's
+ * "auto_attach" handler.  The "auto_attach" handler may call
+ * comedi_to_usb_interface() on the passed in COMEDI device to recover @intf.
+ *
+ * Return: The result of calling comedi_auto_config() (%0 on success, or
+ * a negative error number on failure).
+ */
+int comedi_usb_auto_config(struct usb_interface *intf,
+			   struct comedi_driver *driver,
+			   unsigned long context)
+{
+	return comedi_auto_config(&intf->dev, driver, context);
+}
+EXPORT_SYMBOL_GPL(comedi_usb_auto_config);
+
+/**
+ * comedi_usb_auto_unconfig() - Unconfigure/disconnect a USB COMEDI device
+ * @intf: USB interface.
+ *
+ * Typically called from the usb_driver (*disconnect) function.
+ * Auto-unconfigure a COMEDI device attached to this USB interface, using a
+ * pointer to the &struct device embedded in *@intf as the hardware device.
+ * The COMEDI driver's "detach" handler will be called during unconfiguration
+ * of the COMEDI device.
+ *
+ * Note that the COMEDI device may have already been unconfigured using the
+ * %COMEDI_DEVCONFIG ioctl, in which case this attempt to unconfigure it
+ * again should be ignored.
+ */
+void comedi_usb_auto_unconfig(struct usb_interface *intf)
+{
+	comedi_auto_unconfig(&intf->dev);
+}
+EXPORT_SYMBOL_GPL(comedi_usb_auto_unconfig);
+
+/**
+ * comedi_usb_driver_register() - Register a USB COMEDI driver
+ * @comedi_driver: COMEDI driver to be registered.
+ * @usb_driver: USB driver to be registered.
+ *
+ * This function is called from the module_init() of USB COMEDI driver modules
+ * to register the COMEDI driver and the USB driver.  Do not call it directly,
+ * use the module_comedi_usb_driver() helper macro instead.
+ *
+ * Return: %0 on success, or a negative error number on failure.
+ */
+int comedi_usb_driver_register(struct comedi_driver *comedi_driver,
+			       struct usb_driver *usb_driver)
+{
+	int ret;
+
+	ret = comedi_driver_register(comedi_driver);
+	if (ret < 0)
+		return ret;
+
+	ret = usb_register(usb_driver);
+	if (ret < 0) {
+		comedi_driver_unregister(comedi_driver);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(comedi_usb_driver_register);
+
+/**
+ * comedi_usb_driver_unregister() - Unregister a USB COMEDI driver
+ * @comedi_driver: COMEDI driver to be registered.
+ * @usb_driver: USB driver to be registered.
+ *
+ * This function is called from the module_exit() of USB COMEDI driver modules
+ * to unregister the USB driver and the COMEDI driver.  Do not call it
+ * directly, use the module_comedi_usb_driver() helper macro instead.
+ */
+void comedi_usb_driver_unregister(struct comedi_driver *comedi_driver,
+				  struct usb_driver *usb_driver)
+{
+	usb_deregister(usb_driver);
+	comedi_driver_unregister(comedi_driver);
+}
+EXPORT_SYMBOL_GPL(comedi_usb_driver_unregister);
+
+MODULE_AUTHOR("https://www.comedi.org");
+MODULE_DESCRIPTION("Comedi USB interface module");
+MODULE_LICENSE("GPL");