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, 91 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap-ram.c b/drivers/base/regmap/regmap-ram.c
new file mode 100644
index 000000000..c7356b0d8
--- /dev/null
+++ b/drivers/base/regmap/regmap-ram.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Register map access API - Memory region
+//
+// This is intended for testing only
+//
+// Copyright (c) 2023, Arm Ltd
+
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/swab.h>
+
+#include "internal.h"
+
+static int regmap_ram_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct regmap_ram_data *data = context;
+
+	data->vals[reg] = val;
+	data->written[reg] = true;
+
+	return 0;
+}
+
+static int regmap_ram_read(void *context, unsigned int reg, unsigned int *val)
+{
+	struct regmap_ram_data *data = context;
+
+	*val = data->vals[reg];
+	data->read[reg] = true;
+
+	return 0;
+}
+
+static void regmap_ram_free_context(void *context)
+{
+	struct regmap_ram_data *data = context;
+
+	kfree(data->vals);
+	kfree(data->read);
+	kfree(data->written);
+	kfree(data);
+}
+
+static const struct regmap_bus regmap_ram = {
+	.fast_io = true,
+	.reg_write = regmap_ram_write,
+	.reg_read = regmap_ram_read,
+	.free_context = regmap_ram_free_context,
+};
+
+struct regmap *__regmap_init_ram(struct device *dev,
+				 const struct regmap_config *config,
+				 struct regmap_ram_data *data,
+				 struct lock_class_key *lock_key,
+				 const char *lock_name)
+{
+	struct regmap *map;
+
+	if (!config->max_register) {
+		pr_crit("No max_register specified for RAM regmap\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	data->read = kzalloc_objs(bool, config->max_register + 1);
+	if (!data->read)
+		return ERR_PTR(-ENOMEM);
+
+	data->written = kzalloc_objs(bool, config->max_register + 1);
+	if (!data->written) {
+		kfree(data->read);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	map = __regmap_init(dev, &regmap_ram, data, config,
+			    lock_key, lock_name);
+	if (IS_ERR(map)) {
+		kfree(data->read);
+		kfree(data->written);
+	}
+
+	return map;
+}
+EXPORT_SYMBOL_GPL(__regmap_init_ram);
+
+MODULE_DESCRIPTION("Register map access API - Memory region");
+MODULE_LICENSE("GPL v2");