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, 74 insertions, 0 deletions

diff --git a/drivers/comedi/proc.c b/drivers/comedi/proc.c
new file mode 100644
index 000000000..2e4496633
--- /dev/null
+++ b/drivers/comedi/proc.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * /proc interface for comedi
+ *
+ * COMEDI - Linux Control and Measurement Device Interface
+ * Copyright (C) 1998 David A. Schleef <ds@schleef.org>
+ */
+
+/*
+ * This is some serious bloatware.
+ *
+ * Taken from Dave A.'s PCL-711 driver, 'cuz I thought it
+ * was cool.
+ */
+
+#include <linux/comedi/comedidev.h>
+#include "comedi_internal.h"
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+
+static int comedi_read(struct seq_file *m, void *v)
+{
+	int i;
+	int devices_q = 0;
+	struct comedi_driver *driv;
+
+	seq_printf(m, "comedi version " COMEDI_RELEASE "\nformat string: %s\n",
+		   "\"%2d: %-20s %-20s %4d\", i, driver_name, board_name, n_subdevices");
+
+	for (i = 0; i < COMEDI_NUM_BOARD_MINORS; i++) {
+		struct comedi_device *dev = comedi_dev_get_from_minor(i);
+
+		if (!dev)
+			continue;
+
+		down_read(&dev->attach_lock);
+		if (dev->attached) {
+			devices_q = 1;
+			seq_printf(m, "%2d: %-20s %-20s %4d\n",
+				   i, dev->driver->driver_name,
+				   dev->board_name, dev->n_subdevices);
+		}
+		up_read(&dev->attach_lock);
+		comedi_dev_put(dev);
+	}
+	if (!devices_q)
+		seq_puts(m, "no devices\n");
+
+	mutex_lock(&comedi_drivers_list_lock);
+	for (driv = comedi_drivers; driv; driv = driv->next) {
+		seq_printf(m, "%s:\n", driv->driver_name);
+		for (i = 0; i < driv->num_names; i++)
+			seq_printf(m, " %s\n",
+				   *(char **)((char *)driv->board_name +
+					      i * driv->offset));
+
+		if (!driv->num_names)
+			seq_printf(m, " %s\n", driv->driver_name);
+	}
+	mutex_unlock(&comedi_drivers_list_lock);
+
+	return 0;
+}
+
+void __init comedi_proc_init(void)
+{
+	if (!proc_create_single("comedi", 0444, NULL, comedi_read))
+		pr_warn("comedi: unable to create proc entry\n");
+}
+
+void comedi_proc_cleanup(void)
+{
+	remove_proc_entry("comedi", NULL);
+}