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, 95 insertions, 0 deletions

diff --git a/drivers/mtd/maps/solutionengine.c b/drivers/mtd/maps/solutionengine.c
new file mode 100644
index 000000000..c07f21b20
--- /dev/null
+++ b/drivers/mtd/maps/solutionengine.c
@@ -0,0 +1,95 @@
+/*
+ * Flash and EPROM on Hitachi Solution Engine and similar boards.
+ *
+ * (C) 2001 Red Hat, Inc.
+ *
+ * GPL'd
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <asm/io.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/partitions.h>
+#include <linux/errno.h>
+
+static struct mtd_info *flash_mtd;
+static struct mtd_info *eprom_mtd;
+
+struct map_info soleng_eprom_map = {
+	.name = "Solution Engine EPROM",
+	.size = 0x400000,
+	.bankwidth = 4,
+};
+
+struct map_info soleng_flash_map = {
+	.name = "Solution Engine FLASH",
+	.size = 0x400000,
+	.bankwidth = 4,
+};
+
+static const char * const probes[] = { "RedBoot", "cmdlinepart", NULL };
+
+static int __init init_soleng_maps(void)
+{
+	/* First probe at offset 0 */
+	soleng_flash_map.phys = 0;
+	soleng_flash_map.virt = (void __iomem *)P2SEGADDR(0);
+	soleng_eprom_map.phys = 0x01000000;
+	soleng_eprom_map.virt = (void __iomem *)P1SEGADDR(0x01000000);
+	simple_map_init(&soleng_eprom_map);
+	simple_map_init(&soleng_flash_map);
+
+	printk(KERN_NOTICE "Probing for flash chips at 0x00000000:\n");
+	flash_mtd = do_map_probe("cfi_probe", &soleng_flash_map);
+	if (!flash_mtd) {
+		/* Not there. Try swapping */
+		printk(KERN_NOTICE "Probing for flash chips at 0x01000000:\n");
+		soleng_flash_map.phys = 0x01000000;
+		soleng_flash_map.virt = P2SEGADDR(0x01000000);
+		soleng_eprom_map.phys = 0;
+		soleng_eprom_map.virt = P1SEGADDR(0);
+		flash_mtd = do_map_probe("cfi_probe", &soleng_flash_map);
+		if (!flash_mtd) {
+			/* Eep. */
+			printk(KERN_NOTICE "Flash chips not detected at either possible location.\n");
+			return -ENXIO;
+		}
+	}
+	printk(KERN_NOTICE "Solution Engine: Flash at 0x%pap, EPROM at 0x%pap\n",
+	       &soleng_flash_map.phys,
+	       &soleng_eprom_map.phys);
+	flash_mtd->owner = THIS_MODULE;
+
+	eprom_mtd = do_map_probe("map_rom", &soleng_eprom_map);
+	if (eprom_mtd) {
+		eprom_mtd->owner = THIS_MODULE;
+		mtd_device_register(eprom_mtd, NULL, 0);
+	}
+
+	mtd_device_parse_register(flash_mtd, probes, NULL, NULL, 0);
+
+	return 0;
+}
+
+static void __exit cleanup_soleng_maps(void)
+{
+	if (eprom_mtd) {
+		mtd_device_unregister(eprom_mtd);
+		map_destroy(eprom_mtd);
+	}
+
+	mtd_device_unregister(flash_mtd);
+	map_destroy(flash_mtd);
+}
+
+module_init(init_soleng_maps);
+module_exit(cleanup_soleng_maps);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
+MODULE_DESCRIPTION("MTD map driver for Hitachi SolutionEngine (and similar) boards");
+