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, 187 insertions, 0 deletions

diff --git a/drivers/mcb/mcb-lpc.c b/drivers/mcb/mcb-lpc.c
new file mode 100644
index 000000000..070aa787a
--- /dev/null
+++ b/drivers/mcb/mcb-lpc.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * MEN Chameleon Bus.
+ *
+ * Copyright (C) 2014 MEN Mikroelektronik GmbH (www.men.de)
+ * Author: Andreas Werner <andreas.werner@men.de>
+ */
+
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <linux/dmi.h>
+#include <linux/mcb.h>
+#include <linux/io.h>
+#include "mcb-internal.h"
+
+struct priv {
+	struct mcb_bus *bus;
+	struct resource *mem;
+	void __iomem *base;
+};
+
+static int mcb_lpc_probe(struct platform_device *pdev)
+{
+	struct resource *res;
+	struct priv *priv;
+	int ret = 0, table_size;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!priv->mem) {
+		dev_err(&pdev->dev, "No Memory resource\n");
+		return -ENODEV;
+	}
+
+	res = devm_request_mem_region(&pdev->dev, priv->mem->start,
+				      resource_size(priv->mem),
+				      KBUILD_MODNAME);
+	if (!res) {
+		dev_err(&pdev->dev, "Failed to request IO memory\n");
+		return -EBUSY;
+	}
+
+	priv->base = devm_ioremap(&pdev->dev, priv->mem->start,
+				  resource_size(priv->mem));
+	if (!priv->base) {
+		dev_err(&pdev->dev, "Cannot ioremap\n");
+		return -ENOMEM;
+	}
+
+	platform_set_drvdata(pdev, priv);
+
+	priv->bus = mcb_alloc_bus(&pdev->dev);
+	if (IS_ERR(priv->bus))
+		return PTR_ERR(priv->bus);
+
+	ret = chameleon_parse_cells(priv->bus, priv->mem->start, priv->base);
+	if (ret < 0) {
+		goto out_mcb_bus;
+	}
+
+	table_size = ret;
+
+	if (table_size < CHAM_HEADER_SIZE) {
+		/* Release the previous resources */
+		devm_iounmap(&pdev->dev, priv->base);
+		devm_release_mem_region(&pdev->dev, priv->mem->start, resource_size(priv->mem));
+
+		/* Then, allocate it again with the actual chameleon table size */
+		res = devm_request_mem_region(&pdev->dev, priv->mem->start,
+					      table_size,
+					      KBUILD_MODNAME);
+		if (!res) {
+			dev_err(&pdev->dev, "Failed to request PCI memory\n");
+			ret = -EBUSY;
+			goto out_mcb_bus;
+		}
+
+		priv->base = devm_ioremap(&pdev->dev, priv->mem->start, table_size);
+		if (!priv->base) {
+			dev_err(&pdev->dev, "Cannot ioremap\n");
+			ret = -ENOMEM;
+			goto out_mcb_bus;
+		}
+
+		platform_set_drvdata(pdev, priv);
+	}
+
+	mcb_bus_add_devices(priv->bus);
+
+	return 0;
+
+out_mcb_bus:
+	mcb_release_bus(priv->bus);
+	return ret;
+}
+
+static void mcb_lpc_remove(struct platform_device *pdev)
+{
+	struct priv *priv = platform_get_drvdata(pdev);
+
+	mcb_release_bus(priv->bus);
+}
+
+static struct platform_device *mcb_lpc_pdev;
+
+static int mcb_lpc_create_platform_device(const struct dmi_system_id *id)
+{
+	struct resource *res = id->driver_data;
+	int ret;
+
+	mcb_lpc_pdev = platform_device_alloc("mcb-lpc", -1);
+	if (!mcb_lpc_pdev)
+		return -ENOMEM;
+
+	ret = platform_device_add_resources(mcb_lpc_pdev, res, 1);
+	if (ret)
+		goto out_put;
+
+	ret = platform_device_add(mcb_lpc_pdev);
+	if (ret)
+		goto out_put;
+
+	return 0;
+
+out_put:
+	platform_device_put(mcb_lpc_pdev);
+	return ret;
+}
+
+static struct resource sc24_fpga_resource = DEFINE_RES_MEM(0xe000e000, CHAM_HEADER_SIZE);
+static struct resource sc31_fpga_resource = DEFINE_RES_MEM(0xf000e000, CHAM_HEADER_SIZE);
+
+static struct platform_driver mcb_lpc_driver = {
+	.driver		= {
+		.name = "mcb-lpc",
+	},
+	.probe		= mcb_lpc_probe,
+	.remove		= mcb_lpc_remove,
+};
+
+static const struct dmi_system_id mcb_lpc_dmi_table[] = {
+	{
+		.ident = "SC24",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "MEN"),
+			DMI_MATCH(DMI_PRODUCT_VERSION, "14SC24"),
+		},
+		.driver_data = (void *)&sc24_fpga_resource,
+		.callback = mcb_lpc_create_platform_device,
+	},
+	{
+		.ident = "SC31",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "MEN"),
+			DMI_MATCH(DMI_PRODUCT_VERSION, "14SC31"),
+		},
+		.driver_data = (void *)&sc31_fpga_resource,
+		.callback = mcb_lpc_create_platform_device,
+	},
+	{}
+};
+MODULE_DEVICE_TABLE(dmi, mcb_lpc_dmi_table);
+
+static int __init mcb_lpc_init(void)
+{
+	if (!dmi_check_system(mcb_lpc_dmi_table))
+		return -ENODEV;
+
+	return platform_driver_register(&mcb_lpc_driver);
+}
+
+static void __exit mcb_lpc_exit(void)
+{
+	platform_device_unregister(mcb_lpc_pdev);
+	platform_driver_unregister(&mcb_lpc_driver);
+}
+
+module_init(mcb_lpc_init);
+module_exit(mcb_lpc_exit);
+
+MODULE_AUTHOR("Andreas Werner <andreas.werner@men.de>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("MCB over LPC support");
+MODULE_IMPORT_NS("MCB");