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/rtc/rtc-ps3.c b/drivers/rtc/rtc-ps3.c
new file mode 100644
index 000000000..6b098734c
--- /dev/null
+++ b/drivers/rtc/rtc-ps3.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * PS3 RTC Driver
+ *
+ * Copyright 2009 Sony Corporation
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#include <asm/lv1call.h>
+#include <asm/ps3.h>
+
+
+static u64 read_rtc(void)
+{
+	int result;
+	u64 rtc_val;
+	u64 tb_val;
+
+	result = lv1_get_rtc(&rtc_val, &tb_val);
+	BUG_ON(result);
+
+	return rtc_val;
+}
+
+static int ps3_get_time(struct device *dev, struct rtc_time *tm)
+{
+	rtc_time64_to_tm(read_rtc() + ps3_os_area_get_rtc_diff(), tm);
+	return 0;
+}
+
+static int ps3_set_time(struct device *dev, struct rtc_time *tm)
+{
+	ps3_os_area_set_rtc_diff(rtc_tm_to_time64(tm) - read_rtc());
+	return 0;
+}
+
+static const struct rtc_class_ops ps3_rtc_ops = {
+	.read_time = ps3_get_time,
+	.set_time = ps3_set_time,
+};
+
+static int __init ps3_rtc_probe(struct platform_device *dev)
+{
+	struct rtc_device *rtc;
+
+	rtc = devm_rtc_allocate_device(&dev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &ps3_rtc_ops;
+	rtc->range_max = U64_MAX;
+
+	platform_set_drvdata(dev, rtc);
+
+	return devm_rtc_register_device(rtc);
+}
+
+static struct platform_driver ps3_rtc_driver = {
+	.driver = {
+		.name = "rtc-ps3",
+	},
+};
+
+module_platform_driver_probe(ps3_rtc_driver, ps3_rtc_probe);
+
+MODULE_AUTHOR("Sony Corporation");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ps3 RTC driver");
+MODULE_ALIAS("platform:rtc-ps3");