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, 194 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-wilco-ec.c b/drivers/rtc/rtc-wilco-ec.c
new file mode 100644
index 000000000..2a205a646
--- /dev/null
+++ b/drivers/rtc/rtc-wilco-ec.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * RTC interface for Wilco Embedded Controller with R/W abilities
+ *
+ * Copyright 2018 Google LLC
+ *
+ * The corresponding platform device is typically registered in
+ * drivers/platform/chrome/wilco_ec/core.c
+ */
+
+#include <linux/bcd.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/platform_data/wilco-ec.h>
+#include <linux/rtc.h>
+#include <linux/timekeeping.h>
+
+#define EC_COMMAND_CMOS			0x7c
+#define EC_CMOS_TOD_WRITE		0x02
+#define EC_CMOS_TOD_READ		0x08
+
+/* Message sent to the EC to request the current time. */
+struct ec_rtc_read_request {
+	u8 command;
+	u8 reserved;
+	u8 param;
+} __packed;
+static struct ec_rtc_read_request read_rq = {
+	.command = EC_COMMAND_CMOS,
+	.param = EC_CMOS_TOD_READ,
+};
+
+/**
+ * struct ec_rtc_read_response - Format of RTC returned by EC.
+ * @reserved: Unused byte
+ * @second: Second value (0..59)
+ * @minute: Minute value (0..59)
+ * @hour: Hour value (0..23)
+ * @day: Day value (1..31)
+ * @month: Month value (1..12)
+ * @year: Year value (full year % 100)
+ * @century: Century value (full year / 100)
+ *
+ * All values are presented in binary (not BCD).
+ */
+struct ec_rtc_read_response {
+	u8 reserved;
+	u8 second;
+	u8 minute;
+	u8 hour;
+	u8 day;
+	u8 month;
+	u8 year;
+	u8 century;
+} __packed;
+
+/**
+ * struct ec_rtc_write_request - Format of RTC sent to the EC.
+ * @command: Always EC_COMMAND_CMOS
+ * @reserved: Unused byte
+ * @param: Always EC_CMOS_TOD_WRITE
+ * @century: Century value (full year / 100)
+ * @year: Year value (full year % 100)
+ * @month: Month value (1..12)
+ * @day: Day value (1..31)
+ * @hour: Hour value (0..23)
+ * @minute: Minute value (0..59)
+ * @second: Second value (0..59)
+ * @weekday: Day of the week (0=Saturday)
+ *
+ * All values are presented in BCD.
+ */
+struct ec_rtc_write_request {
+	u8 command;
+	u8 reserved;
+	u8 param;
+	u8 century;
+	u8 year;
+	u8 month;
+	u8 day;
+	u8 hour;
+	u8 minute;
+	u8 second;
+	u8 weekday;
+} __packed;
+
+static int wilco_ec_rtc_read(struct device *dev, struct rtc_time *tm)
+{
+	struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
+	struct ec_rtc_read_response rtc;
+	struct wilco_ec_message msg;
+	int ret;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.type = WILCO_EC_MSG_LEGACY;
+	msg.request_data = &read_rq;
+	msg.request_size = sizeof(read_rq);
+	msg.response_data = &rtc;
+	msg.response_size = sizeof(rtc);
+
+	ret = wilco_ec_mailbox(ec, &msg);
+	if (ret < 0)
+		return ret;
+
+	tm->tm_sec	= rtc.second;
+	tm->tm_min	= rtc.minute;
+	tm->tm_hour	= rtc.hour;
+	tm->tm_mday	= rtc.day;
+	tm->tm_mon	= rtc.month - 1;
+	tm->tm_year	= rtc.year + (rtc.century * 100) - 1900;
+	/* Ignore other tm fields, man rtc says userspace shouldn't use them. */
+
+	if (rtc_valid_tm(tm)) {
+		dev_err(dev, "Time from RTC is invalid: %ptRr\n", tm);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int wilco_ec_rtc_write(struct device *dev, struct rtc_time *tm)
+{
+	struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
+	struct ec_rtc_write_request rtc;
+	struct wilco_ec_message msg;
+	int year = tm->tm_year + 1900;
+	/*
+	 * Convert from 0=Sunday to 0=Saturday for the EC
+	 * We DO need to set weekday because the EC controls battery charging
+	 * schedules that depend on the day of the week.
+	 */
+	int wday = tm->tm_wday == 6 ? 0 : tm->tm_wday + 1;
+	int ret;
+
+	rtc.command	= EC_COMMAND_CMOS;
+	rtc.param	= EC_CMOS_TOD_WRITE;
+	rtc.century	= bin2bcd(year / 100);
+	rtc.year	= bin2bcd(year % 100);
+	rtc.month	= bin2bcd(tm->tm_mon + 1);
+	rtc.day		= bin2bcd(tm->tm_mday);
+	rtc.hour	= bin2bcd(tm->tm_hour);
+	rtc.minute	= bin2bcd(tm->tm_min);
+	rtc.second	= bin2bcd(tm->tm_sec);
+	rtc.weekday	= bin2bcd(wday);
+
+	memset(&msg, 0, sizeof(msg));
+	msg.type = WILCO_EC_MSG_LEGACY;
+	msg.request_data = &rtc;
+	msg.request_size = sizeof(rtc);
+
+	ret = wilco_ec_mailbox(ec, &msg);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static const struct rtc_class_ops wilco_ec_rtc_ops = {
+	.read_time = wilco_ec_rtc_read,
+	.set_time = wilco_ec_rtc_write,
+};
+
+static int wilco_ec_rtc_probe(struct platform_device *pdev)
+{
+	struct rtc_device *rtc;
+
+	rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &wilco_ec_rtc_ops;
+	/* EC only supports this century */
+	rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rtc->range_max = RTC_TIMESTAMP_END_2099;
+	rtc->owner = THIS_MODULE;
+
+	return devm_rtc_register_device(rtc);
+}
+
+static struct platform_driver wilco_ec_rtc_driver = {
+	.driver = {
+		.name = "rtc-wilco-ec",
+	},
+	.probe = wilco_ec_rtc_probe,
+};
+
+module_platform_driver(wilco_ec_rtc_driver);
+
+MODULE_ALIAS("platform:rtc-wilco-ec");
+MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Wilco EC RTC driver");