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, 142 insertions, 0 deletions

diff --git a/drivers/dio/dio-driver.c b/drivers/dio/dio-driver.c
new file mode 100644
index 000000000..12fa2d209
--- /dev/null
+++ b/drivers/dio/dio-driver.c
@@ -0,0 +1,142 @@
+/*
+ *  DIO Driver Services
+ *
+ *  Copyright (C) 2004 Jochen Friedrich
+ *
+ *  Loosely based on drivers/pci/pci-driver.c and drivers/zorro/zorro-driver.c
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of this archive
+ *  for more details.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/dio.h>
+
+
+/**
+ *  dio_match_device - Tell if a DIO device structure has a matching DIO device id structure
+ *  @ids: array of DIO device id structures to search in
+ *  @d: the DIO device structure to match against
+ *
+ *  Used by a driver to check whether a DIO device present in the
+ *  system is in its list of supported devices. Returns the matching
+ *  dio_device_id structure or %NULL if there is no match.
+ */
+
+static const struct dio_device_id *
+dio_match_device(const struct dio_device_id *ids,
+		   const struct dio_dev *d)
+{
+	while (ids->id) {
+		if (ids->id == DIO_WILDCARD)
+			return ids;
+		if (DIO_NEEDSSECID(ids->id & 0xff)) {
+			if (ids->id == d->id)
+				return ids;
+		} else {
+			if ((ids->id & 0xff) == (d->id & 0xff))
+				return ids;
+		}
+		ids++;
+	}
+	return NULL;
+}
+
+static int dio_device_probe(struct device *dev)
+{
+	int error = 0;
+	struct dio_driver *drv = to_dio_driver(dev->driver);
+	struct dio_dev *d = to_dio_dev(dev);
+
+	if (!d->driver && drv->probe) {
+		const struct dio_device_id *id;
+
+		id = dio_match_device(drv->id_table, d);
+		if (id)
+			error = drv->probe(d, id);
+		if (error >= 0) {
+			d->driver = drv;
+			error = 0;
+		}
+	}
+	return error;
+}
+
+
+/**
+ *  dio_register_driver - register a new DIO driver
+ *  @drv: the driver structure to register
+ *
+ *  Adds the driver structure to the list of registered drivers
+ *  Returns zero or a negative error value.
+ */
+
+int dio_register_driver(struct dio_driver *drv)
+{
+	/* initialize common driver fields */
+	drv->driver.name = drv->name;
+	drv->driver.bus = &dio_bus_type;
+
+	/* register with core */
+	return driver_register(&drv->driver);
+}
+
+
+/**
+ *  dio_unregister_driver - unregister a DIO driver
+ *  @drv: the driver structure to unregister
+ *
+ *  Deletes the driver structure from the list of registered DIO drivers,
+ *  gives it a chance to clean up by calling its remove() function for
+ *  each device it was responsible for, and marks those devices as
+ *  driverless.
+ */
+
+void dio_unregister_driver(struct dio_driver *drv)
+{
+	driver_unregister(&drv->driver);
+}
+
+
+/**
+ *  dio_bus_match - Tell if a DIO device structure has a matching DIO device id structure
+ *  @dev: the DIO device structure to match against
+ *  @drv: the &device_driver that points to the array of DIO device id structures to search
+ *
+ *  Used by the driver core to check whether a DIO device present in the
+ *  system is in a driver's list of supported devices. Returns 1 if supported,
+ *  and 0 if there is no match.
+ */
+
+static int dio_bus_match(struct device *dev, const struct device_driver *drv)
+{
+	struct dio_dev *d = to_dio_dev(dev);
+	const struct dio_driver *dio_drv = to_dio_driver(drv);
+	const struct dio_device_id *ids = dio_drv->id_table;
+
+	if (!ids)
+		return 0;
+
+	return dio_match_device(ids, d) ? 1 : 0;
+}
+
+
+const struct bus_type dio_bus_type = {
+	.name	= "dio",
+	.match	= dio_bus_match,
+	.probe	= dio_device_probe,
+};
+
+
+static int __init dio_driver_init(void)
+{
+	return bus_register(&dio_bus_type);
+}
+
+postcore_initcall(dio_driver_init);
+
+EXPORT_SYMBOL(dio_register_driver);
+EXPORT_SYMBOL(dio_unregister_driver);
+EXPORT_SYMBOL(dio_bus_type);