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, 68 insertions, 0 deletions

diff --git a/drivers/extcon/extcon.h b/drivers/extcon/extcon.h
new file mode 100644
index 000000000..946182687
--- /dev/null
+++ b/drivers/extcon/extcon.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_EXTCON_INTERNAL_H__
+#define __LINUX_EXTCON_INTERNAL_H__
+
+#include <linux/extcon-provider.h>
+
+/**
+ * struct extcon_dev - An extcon device represents one external connector.
+ * @name:		The name of this extcon device. Parent device name is
+ *			used if NULL.
+ * @supported_cable:	Array of supported cable names ending with EXTCON_NONE.
+ *			If supported_cable is NULL, cable name related APIs
+ *			are disabled.
+ * @mutually_exclusive:	Array of mutually exclusive set of cables that cannot
+ *			be attached simultaneously. The array should be
+ *			ending with 0 or be NULL (no mutually exclusive cables).
+ *			For example, if it is {0x7, 0x30, 0}, then,
+ *			{0, 1}, {0, 1, 2}, {0, 2}, {1, 2}, or {4, 5} cannot
+ *			be attached simulataneously. {0x7, 0} is equivalent to
+ *			{0x3, 0x6, 0x5, 0}. If it is {0xFFFFFFFF, 0}, there
+ *			can be no simultaneous connections.
+ * @dev:		Device of this extcon.
+ * @id:			Unique device ID of this extcon.
+ * @state:		Attach/detach state of this extcon. Do not provide at
+ *			register-time.
+ * @nh_all:		Notifier for the state change events for all supported
+ *			external connectors from this extcon.
+ * @nh:			Notifier for the state change events from this extcon
+ * @entry:		To support list of extcon devices so that users can
+ *			search for extcon devices based on the extcon name.
+ * @lock:		Protects device state and serialises device registration
+ * @max_supported:	Internal value to store the number of cables.
+ * @extcon_dev_type:	Device_type struct to provide attribute_groups
+ *			customized for each extcon device.
+ * @cables:		Sysfs subdirectories. Each represents one cable.
+ *
+ * In most cases, users only need to provide "User initializing data" of
+ * this struct when registering an extcon. In some exceptional cases,
+ * optional callbacks may be needed. However, the values in "internal data"
+ * are overwritten by register function.
+ */
+struct extcon_dev {
+	/* Optional user initializing data */
+	const char *name;
+	const unsigned int *supported_cable;
+	const u32 *mutually_exclusive;
+
+	/* Internal data. Please do not set. */
+	struct device dev;
+	unsigned int id;
+	struct raw_notifier_head nh_all;
+	struct raw_notifier_head *nh;
+	struct list_head entry;
+	int max_supported;
+	spinlock_t lock;	/* could be called by irq handler */
+	u32 state;
+
+	/* /sys/class/extcon/.../cable.n/... */
+	struct device_type extcon_dev_type;
+	struct extcon_cable *cables;
+
+	/* /sys/class/extcon/.../mutually_exclusive/... */
+	struct attribute_group attr_g_muex;
+	struct attribute **attrs_muex;
+	struct device_attribute *d_attrs_muex;
+};
+
+#endif /* __LINUX_EXTCON_INTERNAL_H__ */