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, 40 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/serialio.h b/drivers/accessibility/speakup/serialio.h
new file mode 100644
index 000000000..b4f9a1925
--- /dev/null
+++ b/drivers/accessibility/speakup/serialio.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _SPEAKUP_SERIAL_H
+#define _SPEAKUP_SERIAL_H
+
+#include <linux/serial.h>	/* for rs_table, serial constants */
+#include <linux/serial_reg.h>	/* for more serial constants */
+#include <linux/serial_core.h>
+
+#include "spk_priv.h"
+
+/*
+ * this is cut&paste from 8250.h. Get rid of the structure, the definitions
+ * and this whole broken driver.
+ */
+struct old_serial_port {
+	unsigned int uart; /* unused */
+	unsigned int baud_base;
+	unsigned int port;
+	unsigned int irq;
+	upf_t flags; /* unused */
+};
+
+/* countdown values for serial timeouts in us */
+#define SPK_SERIAL_TIMEOUT SPK_SYNTH_TIMEOUT
+/* countdown values transmitter/dsr timeouts in us */
+#define SPK_XMITR_TIMEOUT 100000
+/* countdown values cts timeouts in us */
+#define SPK_CTS_TIMEOUT 100000
+/* check ttyS0 ... ttyS3 */
+#define SPK_LO_TTY 0
+#define SPK_HI_TTY 3
+/* # of timeouts permitted before disable */
+#define NUM_DISABLE_TIMEOUTS 3
+/* buffer timeout in ms */
+#define SPK_TIMEOUT 100
+
+#define spk_serial_tx_busy() \
+	(!uart_lsr_tx_empty(inb(speakup_info.port_tts + UART_LSR)))
+
+#endif