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, 160 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1672.c b/drivers/rtc/rtc-ds1672.c
new file mode 100644
index 000000000..c610beb55
--- /dev/null
+++ b/drivers/rtc/rtc-ds1672.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * An rtc/i2c driver for the Dallas DS1672
+ * Copyright 2005-06 Tower Technologies
+ *
+ * Author: Alessandro Zummo <a.zummo@towertech.it>
+ */
+
+#include <linux/i2c.h>
+#include <linux/rtc.h>
+#include <linux/module.h>
+
+/* Registers */
+
+#define DS1672_REG_CNT_BASE	0
+#define DS1672_REG_CONTROL	4
+#define DS1672_REG_TRICKLE	5
+
+#define DS1672_REG_CONTROL_EOSC	0x80
+
+/*
+ * In the routines that deal directly with the ds1672 hardware, we use
+ * rtc_time -- month 0-11, hour 0-23, yr = calendar year-epoch
+ * Time is set to UTC.
+ */
+static int ds1672_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	unsigned long time;
+	unsigned char addr = DS1672_REG_CONTROL;
+	unsigned char buf[4];
+
+	struct i2c_msg msgs[] = {
+		{/* setup read ptr */
+			.addr = client->addr,
+			.len = 1,
+			.buf = &addr
+		},
+		{/* read date */
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.len = 1,
+			.buf = buf
+		},
+	};
+
+	/* read control register */
+	if ((i2c_transfer(client->adapter, &msgs[0], 2)) != 2) {
+		dev_warn(&client->dev, "Unable to read the control register\n");
+		return -EIO;
+	}
+
+	if (buf[0] & DS1672_REG_CONTROL_EOSC) {
+		dev_warn(&client->dev, "Oscillator not enabled. Set time to enable.\n");
+		return -EINVAL;
+	}
+
+	addr = DS1672_REG_CNT_BASE;
+	msgs[1].len = 4;
+
+	/* read date registers */
+	if ((i2c_transfer(client->adapter, &msgs[0], 2)) != 2) {
+		dev_err(&client->dev, "%s: read error\n", __func__);
+		return -EIO;
+	}
+
+	dev_dbg(&client->dev,
+		"%s: raw read data - counters=%02x,%02x,%02x,%02x\n",
+		__func__, buf[0], buf[1], buf[2], buf[3]);
+
+	time = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+	       (buf[1] << 8) | buf[0];
+
+	rtc_time64_to_tm(time, tm);
+
+	dev_dbg(&client->dev, "%s: tm is %ptR\n", __func__, tm);
+
+	return 0;
+}
+
+static int ds1672_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int xfer;
+	unsigned char buf[6];
+	unsigned long secs = rtc_tm_to_time64(tm);
+
+	buf[0] = DS1672_REG_CNT_BASE;
+	buf[1] = secs & 0x000000FF;
+	buf[2] = (secs & 0x0000FF00) >> 8;
+	buf[3] = (secs & 0x00FF0000) >> 16;
+	buf[4] = (secs & 0xFF000000) >> 24;
+	buf[5] = 0;		/* set control reg to enable counting */
+
+	xfer = i2c_master_send(client, buf, 6);
+	if (xfer != 6) {
+		dev_err(&client->dev, "%s: send: %d\n", __func__, xfer);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static const struct rtc_class_ops ds1672_rtc_ops = {
+	.read_time = ds1672_read_time,
+	.set_time = ds1672_set_time,
+};
+
+static int ds1672_probe(struct i2c_client *client)
+{
+	int err = 0;
+	struct rtc_device *rtc;
+
+	dev_dbg(&client->dev, "%s\n", __func__);
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	rtc = devm_rtc_allocate_device(&client->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &ds1672_rtc_ops;
+	rtc->range_max = U32_MAX;
+
+	err = devm_rtc_register_device(rtc);
+	if (err)
+		return err;
+
+	i2c_set_clientdata(client, rtc);
+
+	return 0;
+}
+
+static const struct i2c_device_id ds1672_id[] = {
+	{ .name = "ds1672" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ds1672_id);
+
+static const __maybe_unused struct of_device_id ds1672_of_match[] = {
+	{ .compatible = "dallas,ds1672" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ds1672_of_match);
+
+static struct i2c_driver ds1672_driver = {
+	.driver = {
+		   .name = "rtc-ds1672",
+		   .of_match_table = of_match_ptr(ds1672_of_match),
+	},
+	.probe = ds1672_probe,
+	.id_table = ds1672_id,
+};
+
+module_i2c_driver(ds1672_driver);
+
+MODULE_AUTHOR("Alessandro Zummo <a.zummo@towertech.it>");
+MODULE_DESCRIPTION("Dallas/Maxim DS1672 timekeeper driver");
+MODULE_LICENSE("GPL");