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, 92 insertions, 0 deletions

diff --git a/drivers/rtc/proc.c b/drivers/rtc/proc.c
new file mode 100644
index 000000000..cbcdbb19d
--- /dev/null
+++ b/drivers/rtc/proc.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * RTC subsystem, proc interface
+ *
+ * Copyright (C) 2005-06 Tower Technologies
+ * Author: Alessandro Zummo <a.zummo@towertech.it>
+ *
+ * based on arch/arm/common/rtctime.c
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+
+#include "rtc-core.h"
+
+#define NAME_SIZE	10
+
+#if defined(CONFIG_RTC_HCTOSYS_DEVICE)
+static bool is_rtc_hctosys(struct rtc_device *rtc)
+{
+	int size;
+	char name[NAME_SIZE];
+
+	size = snprintf(name, NAME_SIZE, "rtc%d", rtc->id);
+	if (size >= NAME_SIZE)
+		return false;
+
+	return !strncmp(name, CONFIG_RTC_HCTOSYS_DEVICE, NAME_SIZE);
+}
+#else
+static bool is_rtc_hctosys(struct rtc_device *rtc)
+{
+	return (rtc->id == 0);
+}
+#endif
+
+static int rtc_proc_show(struct seq_file *seq, void *offset)
+{
+	int err;
+	struct rtc_device *rtc = seq->private;
+	const struct rtc_class_ops *ops = rtc->ops;
+	struct rtc_wkalrm alrm;
+	struct rtc_time tm;
+
+	err = rtc_read_time(rtc, &tm);
+	if (err == 0) {
+		seq_printf(seq,
+			   "rtc_time\t: %ptRt\n"
+			   "rtc_date\t: %ptRd\n",
+			   &tm, &tm);
+	}
+
+	err = rtc_read_alarm(rtc, &alrm);
+	if (err == 0) {
+		seq_printf(seq, "alrm_time\t: %ptRt\n", &alrm.time);
+		seq_printf(seq, "alrm_date\t: %ptRd\n", &alrm.time);
+		seq_printf(seq, "alarm_IRQ\t: %s\n",
+			   alrm.enabled ? "yes" : "no");
+		seq_printf(seq, "alrm_pending\t: %s\n",
+			   alrm.pending ? "yes" : "no");
+		seq_printf(seq, "update IRQ enabled\t: %s\n",
+			   (rtc->uie_rtctimer.enabled) ? "yes" : "no");
+		seq_printf(seq, "periodic IRQ enabled\t: %s\n",
+			   (rtc->pie_enabled) ? "yes" : "no");
+		seq_printf(seq, "periodic IRQ frequency\t: %d\n",
+			   rtc->irq_freq);
+		seq_printf(seq, "max user IRQ frequency\t: %d\n",
+			   rtc->max_user_freq);
+	}
+
+	seq_printf(seq, "24hr\t\t: yes\n");
+
+	if (ops->proc)
+		ops->proc(rtc->dev.parent, seq);
+
+	return 0;
+}
+
+void rtc_proc_add_device(struct rtc_device *rtc)
+{
+	if (is_rtc_hctosys(rtc))
+		proc_create_single_data("driver/rtc", 0, NULL, rtc_proc_show,
+					rtc);
+}
+
+void rtc_proc_del_device(struct rtc_device *rtc)
+{
+	if (is_rtc_hctosys(rtc))
+		remove_proc_entry("driver/rtc", NULL);
+}