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, 171 insertions, 0 deletions

diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
new file mode 100644
index 000000000..9e2a18c0b
--- /dev/null
+++ b/drivers/usb/serial/bus.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * USB Serial Converter Bus specific functions
+ *
+ * Copyright (C) 2002 Greg Kroah-Hartman (greg@kroah.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/tty.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+static int usb_serial_device_match(struct device *dev,
+				   const struct device_driver *drv)
+{
+	const struct usb_serial_port *port = to_usb_serial_port(dev);
+	const struct usb_serial_driver *driver = to_usb_serial_driver(drv);
+
+	/*
+	 * drivers are already assigned to ports in serial_probe so it's
+	 * a simple check here.
+	 */
+	if (driver == port->serial->type)
+		return 1;
+
+	return 0;
+}
+
+static int usb_serial_device_probe(struct device *dev)
+{
+	struct usb_serial_port *port = to_usb_serial_port(dev);
+	struct usb_serial_driver *driver;
+	struct device *tty_dev;
+	int retval = 0;
+	int minor;
+
+	/* make sure suspend/resume doesn't race against port_probe */
+	retval = usb_autopm_get_interface(port->serial->interface);
+	if (retval)
+		return retval;
+
+	driver = port->serial->type;
+	if (driver->port_probe) {
+		retval = driver->port_probe(port);
+		if (retval)
+			goto err_autopm_put;
+	}
+
+	minor = port->minor;
+	tty_dev = tty_port_register_device(&port->port, usb_serial_tty_driver,
+					   minor, dev);
+	if (IS_ERR(tty_dev)) {
+		retval = PTR_ERR(tty_dev);
+		goto err_port_remove;
+	}
+
+	usb_autopm_put_interface(port->serial->interface);
+
+	dev_info(&port->serial->dev->dev,
+		 "%s converter now attached to ttyUSB%d\n",
+		 driver->description, minor);
+
+	return 0;
+
+err_port_remove:
+	if (driver->port_remove)
+		driver->port_remove(port);
+err_autopm_put:
+	usb_autopm_put_interface(port->serial->interface);
+
+	return retval;
+}
+
+static void usb_serial_device_remove(struct device *dev)
+{
+	struct usb_serial_port *port = to_usb_serial_port(dev);
+	struct usb_serial_driver *driver;
+	int minor;
+	int autopm_err;
+
+	/*
+	 * Make sure suspend/resume doesn't race against port_remove.
+	 *
+	 * Note that no further runtime PM callbacks will be made if
+	 * autopm_get fails.
+	 */
+	autopm_err = usb_autopm_get_interface(port->serial->interface);
+
+	minor = port->minor;
+	tty_unregister_device(usb_serial_tty_driver, minor);
+
+	driver = port->serial->type;
+	if (driver->port_remove)
+		driver->port_remove(port);
+
+	dev_info(dev, "%s converter now disconnected from ttyUSB%d\n",
+		 driver->description, minor);
+
+	if (!autopm_err)
+		usb_autopm_put_interface(port->serial->interface);
+}
+
+static ssize_t new_id_store(struct device_driver *driver,
+			    const char *buf, size_t count)
+{
+	struct usb_serial_driver *usb_drv = to_usb_serial_driver(driver);
+	ssize_t retval = usb_store_new_id(&usb_drv->dynids, usb_drv->id_table,
+					 driver, buf, count);
+
+	if (retval >= 0 && usb_drv->usb_driver != NULL)
+		retval = usb_store_new_id(&usb_drv->usb_driver->dynids,
+					  usb_drv->usb_driver->id_table,
+					  &usb_drv->usb_driver->driver,
+					  buf, count);
+	return retval;
+}
+
+static ssize_t new_id_show(struct device_driver *driver, char *buf)
+{
+	struct usb_serial_driver *usb_drv = to_usb_serial_driver(driver);
+
+	return usb_show_dynids(&usb_drv->dynids, buf);
+}
+static DRIVER_ATTR_RW(new_id);
+
+static struct attribute *usb_serial_drv_attrs[] = {
+	&driver_attr_new_id.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(usb_serial_drv);
+
+static void free_dynids(struct usb_serial_driver *drv)
+{
+	struct usb_dynid *dynid, *n;
+
+	guard(mutex)(&usb_dynids_lock);
+	list_for_each_entry_safe(dynid, n, &drv->dynids.list, node) {
+		list_del(&dynid->node);
+		kfree(dynid);
+	}
+}
+
+const struct bus_type usb_serial_bus_type = {
+	.name =		"usb-serial",
+	.match =	usb_serial_device_match,
+	.probe =	usb_serial_device_probe,
+	.remove =	usb_serial_device_remove,
+	.drv_groups = 	usb_serial_drv_groups,
+};
+
+int usb_serial_bus_register(struct usb_serial_driver *driver)
+{
+	int retval;
+
+	driver->driver.bus = &usb_serial_bus_type;
+	INIT_LIST_HEAD(&driver->dynids.list);
+
+	retval = driver_register(&driver->driver);
+
+	return retval;
+}
+
+void usb_serial_bus_deregister(struct usb_serial_driver *driver)
+{
+	free_dynids(driver);
+	driver_unregister(&driver->driver);
+}
+