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, 73 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/tsc2004.c b/drivers/input/touchscreen/tsc2004.c
new file mode 100644
index 000000000..130aeb735
--- /dev/null
+++ b/drivers/input/touchscreen/tsc2004.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * TSC2004 touchscreen driver
+ *
+ * Copyright (C) 2015 QWERTY Embedded Design
+ * Copyright (C) 2015 EMAC Inc.
+ */
+
+#include <linux/module.h>
+#include <linux/input.h>
+#include <linux/of.h>
+#include <linux/i2c.h>
+#include <linux/regmap.h>
+#include "tsc200x-core.h"
+
+static const struct input_id tsc2004_input_id = {
+	.bustype = BUS_I2C,
+	.product = 2004,
+};
+
+static int tsc2004_cmd(struct device *dev, u8 cmd)
+{
+	u8 tx = TSC200X_CMD | TSC200X_CMD_12BIT | cmd;
+	s32 data;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	data = i2c_smbus_write_byte(i2c, tx);
+	if (data < 0) {
+		dev_err(dev, "%s: failed, command: %x i2c error: %d\n",
+			__func__, cmd, data);
+		return data;
+	}
+
+	return 0;
+}
+
+static int tsc2004_probe(struct i2c_client *i2c)
+
+{
+	return tsc200x_probe(&i2c->dev, i2c->irq, &tsc2004_input_id,
+			     devm_regmap_init_i2c(i2c, &tsc200x_regmap_config),
+			     tsc2004_cmd);
+}
+
+static const struct i2c_device_id tsc2004_idtable[] = {
+	{ .name = "tsc2004" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, tsc2004_idtable);
+
+#ifdef CONFIG_OF
+static const struct of_device_id tsc2004_of_match[] = {
+	{ .compatible = "ti,tsc2004" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, tsc2004_of_match);
+#endif
+
+static struct i2c_driver tsc2004_driver = {
+	.driver = {
+		.name		= "tsc2004",
+		.dev_groups	= tsc200x_groups,
+		.of_match_table	= of_match_ptr(tsc2004_of_match),
+		.pm		= pm_sleep_ptr(&tsc200x_pm_ops),
+	},
+	.id_table       = tsc2004_idtable,
+	.probe          = tsc2004_probe,
+};
+module_i2c_driver(tsc2004_driver);
+
+MODULE_AUTHOR("Michael Welling <mwelling@ieee.org>");
+MODULE_DESCRIPTION("TSC2004 Touchscreen Driver");
+MODULE_LICENSE("GPL");