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, 145 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-r9701.c b/drivers/rtc/rtc-r9701.c
new file mode 100644
index 000000000..60a3c3d74
--- /dev/null
+++ b/drivers/rtc/rtc-r9701.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for Epson RTC-9701JE
+ *
+ * Copyright (C) 2008 Magnus Damm
+ *
+ * Based on rtc-max6902.c
+ *
+ * Copyright (C) 2006 8D Technologies inc.
+ * Copyright (C) 2004 Compulab Ltd.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+#include <linux/delay.h>
+#include <linux/bitops.h>
+
+#define RSECCNT	0x00	/* Second Counter */
+#define RMINCNT	0x01	/* Minute Counter */
+#define RHRCNT	0x02	/* Hour Counter */
+#define RWKCNT	0x03	/* Week Counter */
+#define RDAYCNT	0x04	/* Day Counter */
+#define RMONCNT	0x05	/* Month Counter */
+#define RYRCNT	0x06	/* Year Counter */
+#define R100CNT	0x07	/* Y100 Counter */
+#define RMINAR	0x08	/* Minute Alarm */
+#define RHRAR	0x09	/* Hour Alarm */
+#define RWKAR	0x0a	/* Week/Day Alarm */
+#define RTIMCNT	0x0c	/* Interval Timer */
+#define REXT	0x0d	/* Extension Register */
+#define RFLAG	0x0e	/* RTC Flag Register */
+#define RCR	0x0f	/* RTC Control Register */
+
+static int write_reg(struct device *dev, int address, unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	buf[0] = address & 0x7f;
+	buf[1] = data;
+
+	return spi_write(spi, buf, ARRAY_SIZE(buf));
+}
+
+static int read_regs(struct device *dev, unsigned char *regs, int no_regs)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	u8 txbuf[1], rxbuf[1];
+	int k, ret;
+
+	ret = 0;
+
+	for (k = 0; ret == 0 && k < no_regs; k++) {
+		txbuf[0] = 0x80 | regs[k];
+		ret = spi_write_then_read(spi, txbuf, 1, rxbuf, 1);
+		regs[k] = rxbuf[0];
+	}
+
+	return ret;
+}
+
+static int r9701_get_datetime(struct device *dev, struct rtc_time *dt)
+{
+	int ret;
+	unsigned char buf[] = { RSECCNT, RMINCNT, RHRCNT,
+				RDAYCNT, RMONCNT, RYRCNT };
+
+	ret = read_regs(dev, buf, ARRAY_SIZE(buf));
+	if (ret)
+		return ret;
+
+	dt->tm_sec = bcd2bin(buf[0]); /* RSECCNT */
+	dt->tm_min = bcd2bin(buf[1]); /* RMINCNT */
+	dt->tm_hour = bcd2bin(buf[2]); /* RHRCNT */
+
+	dt->tm_mday = bcd2bin(buf[3]); /* RDAYCNT */
+	dt->tm_mon = bcd2bin(buf[4]) - 1; /* RMONCNT */
+	dt->tm_year = bcd2bin(buf[5]) + 100; /* RYRCNT */
+
+	return 0;
+}
+
+static int r9701_set_datetime(struct device *dev, struct rtc_time *dt)
+{
+	int ret;
+
+	ret = write_reg(dev, RHRCNT, bin2bcd(dt->tm_hour));
+	ret = ret ? ret : write_reg(dev, RMINCNT, bin2bcd(dt->tm_min));
+	ret = ret ? ret : write_reg(dev, RSECCNT, bin2bcd(dt->tm_sec));
+	ret = ret ? ret : write_reg(dev, RDAYCNT, bin2bcd(dt->tm_mday));
+	ret = ret ? ret : write_reg(dev, RMONCNT, bin2bcd(dt->tm_mon + 1));
+	ret = ret ? ret : write_reg(dev, RYRCNT, bin2bcd(dt->tm_year - 100));
+
+	return ret;
+}
+
+static const struct rtc_class_ops r9701_rtc_ops = {
+	.read_time	= r9701_get_datetime,
+	.set_time	= r9701_set_datetime,
+};
+
+static int r9701_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char tmp;
+	int res;
+
+	tmp = R100CNT;
+	res = read_regs(&spi->dev, &tmp, 1);
+	if (res || tmp != 0x20) {
+		dev_err(&spi->dev, "cannot read RTC register\n");
+		return -ENODEV;
+	}
+
+	rtc = devm_rtc_allocate_device(&spi->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+	rtc->ops = &r9701_rtc_ops;
+	rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	return devm_rtc_register_device(rtc);
+}
+
+static struct spi_driver r9701_driver = {
+	.driver = {
+		.name	= "rtc-r9701",
+	},
+	.probe	= r9701_probe,
+};
+
+module_spi_driver(r9701_driver);
+
+MODULE_DESCRIPTION("r9701 spi RTC driver");
+MODULE_AUTHOR("Magnus Damm <damm@opensource.se>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-r9701");