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, 49 insertions, 0 deletions

diff --git a/drivers/usb/class/Kconfig b/drivers/usb/class/Kconfig
new file mode 100644
index 000000000..d3f5162bd
--- /dev/null
+++ b/drivers/usb/class/Kconfig
@@ -0,0 +1,49 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# USB Class driver configuration
+#
+comment "USB Device Class drivers"
+
+config USB_ACM
+	tristate "USB Modem (CDC ACM) support"
+	depends on TTY
+	help
+	  This driver supports USB modems and ISDN adapters which support the
+	  Communication Device Class Abstract Control Model interface.
+	  Please read <file:Documentation/usb/acm.rst> for details.
+
+	  If your modem only reports "Cls=ff(vend.)" in the descriptors in
+	  /sys/kernel/debug/usb/devices, then your modem will not work with this
+	  driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cdc-acm.
+
+config USB_PRINTER
+	tristate "USB Printer support"
+	help
+	  Say Y here if you want to connect a USB printer to your computer's
+	  USB port.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called usblp.
+
+config USB_WDM
+	tristate "USB Wireless Device Management support"
+	help
+	  This driver supports the WMC Device Management functionality
+	  of cell phones compliant to the CDC WMC specification. You can use
+	  AT commands over this device.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cdc-wdm.
+
+config USB_TMC
+	tristate "USB Test and Measurement Class support"
+	help
+	  Say Y here if you want to connect a USB device that follows
+	  the USB.org specification for USB Test and Measurement devices
+	  to your computer's USB port.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called usbtmc.