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, 103 insertions, 0 deletions

diff --git a/drivers/hid/hid-picolcd_backlight.c b/drivers/hid/hid-picolcd_backlight.c
new file mode 100644
index 000000000..4b43b6453
--- /dev/null
+++ b/drivers/hid/hid-picolcd_backlight.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/***************************************************************************
+ *   Copyright (C) 2010-2012 by Bruno Prémont <bonbons@linux-vserver.org>  *
+ *                                                                         *
+ *   Based on Logitech G13 driver (v0.4)                                   *
+ *     Copyright (C) 2009 by Rick L. Vinyard, Jr. <rvinyard@cs.nmsu.edu>   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include <linux/hid.h>
+
+#include <linux/backlight.h>
+
+#include "hid-picolcd.h"
+
+static int picolcd_get_brightness(struct backlight_device *bdev)
+{
+	struct picolcd_data *data = bl_get_data(bdev);
+	return data->lcd_brightness;
+}
+
+static int picolcd_set_brightness(struct backlight_device *bdev)
+{
+	struct picolcd_data *data = bl_get_data(bdev);
+	struct hid_report *report = picolcd_out_report(REPORT_BRIGHTNESS, data->hdev);
+	unsigned long flags;
+
+	if (!report || report->maxfield != 1 || report->field[0]->report_count != 1)
+		return -ENODEV;
+
+	data->lcd_brightness = bdev->props.brightness & 0x0ff;
+	data->lcd_power      = bdev->props.power;
+	spin_lock_irqsave(&data->lock, flags);
+	hid_set_field(report->field[0], 0,
+		      data->lcd_power == BACKLIGHT_POWER_ON ? data->lcd_brightness : 0);
+	if (!(data->status & PICOLCD_FAILED))
+		hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
+	spin_unlock_irqrestore(&data->lock, flags);
+	return 0;
+}
+
+static const struct backlight_ops picolcd_blops = {
+	.update_status  = picolcd_set_brightness,
+	.get_brightness = picolcd_get_brightness,
+};
+
+int picolcd_init_backlight(struct picolcd_data *data, struct hid_report *report)
+{
+	struct device *dev = &data->hdev->dev;
+	struct backlight_device *bdev;
+	struct backlight_properties props;
+	if (!report)
+		return -ENODEV;
+	if (report->maxfield != 1 || report->field[0]->report_count != 1 ||
+			report->field[0]->report_size != 8) {
+		dev_err(dev, "unsupported BRIGHTNESS report");
+		return -EINVAL;
+	}
+
+	memset(&props, 0, sizeof(props));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = 0xff;
+	bdev = backlight_device_register(dev_name(dev), dev, data,
+			&picolcd_blops, &props);
+	if (IS_ERR(bdev)) {
+		dev_err(dev, "failed to register backlight\n");
+		return PTR_ERR(bdev);
+	}
+	bdev->props.brightness     = 0xff;
+	data->lcd_brightness       = 0xff;
+	data->backlight            = bdev;
+	picolcd_set_brightness(bdev);
+	return 0;
+}
+
+void picolcd_exit_backlight(struct picolcd_data *data)
+{
+	struct backlight_device *bdev = data->backlight;
+
+	data->backlight = NULL;
+	backlight_device_unregister(bdev);
+}
+
+int picolcd_resume_backlight(struct picolcd_data *data)
+{
+	if (!data->backlight)
+		return 0;
+	return picolcd_set_brightness(data->backlight);
+}
+
+#ifdef CONFIG_PM
+void picolcd_suspend_backlight(struct picolcd_data *data)
+{
+	int bl_power = data->lcd_power;
+	if (!data->backlight)
+		return;
+
+	data->backlight->props.power = BACKLIGHT_POWER_OFF;
+	picolcd_set_brightness(data->backlight);
+	data->lcd_power = data->backlight->props.power = bl_power;
+}
+#endif /* CONFIG_PM */
+