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, 99 insertions, 0 deletions

diff --git a/drivers/pps/sysfs.c b/drivers/pps/sysfs.c
new file mode 100644
index 000000000..134bc33f6
--- /dev/null
+++ b/drivers/pps/sysfs.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PPS sysfs support
+ *
+ * Copyright (C) 2007-2009   Rodolfo Giometti <giometti@linux.it>
+ */
+
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/pps_kernel.h>
+
+/*
+ * Attribute functions
+ */
+
+static ssize_t assert_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	if (!(pps->info.mode & PPS_CAPTUREASSERT))
+		return 0;
+
+	return sprintf(buf, "%lld.%09d#%d\n",
+			(long long) pps->assert_tu.sec, pps->assert_tu.nsec,
+			pps->assert_sequence);
+}
+static DEVICE_ATTR_RO(assert);
+
+static ssize_t clear_show(struct device *dev, struct device_attribute *attr,
+			  char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	if (!(pps->info.mode & PPS_CAPTURECLEAR))
+		return 0;
+
+	return sprintf(buf, "%lld.%09d#%d\n",
+			(long long) pps->clear_tu.sec, pps->clear_tu.nsec,
+			pps->clear_sequence);
+}
+static DEVICE_ATTR_RO(clear);
+
+static ssize_t mode_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%4x\n", pps->info.mode);
+}
+static DEVICE_ATTR_RO(mode);
+
+static ssize_t echo_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%d\n", !!pps->info.echo);
+}
+static DEVICE_ATTR_RO(echo);
+
+static ssize_t name_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", pps->info.name);
+}
+static DEVICE_ATTR_RO(name);
+
+static ssize_t path_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", pps->info.path);
+}
+static DEVICE_ATTR_RO(path);
+
+static struct attribute *pps_attrs[] = {
+	&dev_attr_assert.attr,
+	&dev_attr_clear.attr,
+	&dev_attr_mode.attr,
+	&dev_attr_echo.attr,
+	&dev_attr_name.attr,
+	&dev_attr_path.attr,
+	NULL,
+};
+
+static const struct attribute_group pps_group = {
+	.attrs = pps_attrs,
+};
+
+const struct attribute_group *pps_groups[] = {
+	&pps_group,
+	NULL,
+};