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, 130 insertions, 0 deletions

diff --git a/drivers/tty/serial/dz.h b/drivers/tty/serial/dz.h
new file mode 100644
index 000000000..3b3e31954
--- /dev/null
+++ b/drivers/tty/serial/dz.h
@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * dz.h: Serial port driver for DECstations equipped
+ *       with the DZ chipset.
+ *
+ * Copyright (C) 1998 Olivier A. D. Lebaillif 
+ *             
+ * Email: olivier.lebaillif@ifrsys.com
+ *
+ * Copyright (C) 2004, 2006  Maciej W. Rozycki
+ */
+#ifndef DZ_SERIAL_H
+#define DZ_SERIAL_H
+
+/*
+ * Definitions for the Control and Status Register.
+ */
+#define DZ_TRDY        0x8000                 /* Transmitter empty */
+#define DZ_TIE         0x4000                 /* Transmitter Interrupt Enbl */
+#define DZ_TLINE       0x0300                 /* Transmitter Line Number */
+#define DZ_RDONE       0x0080                 /* Receiver data ready */
+#define DZ_RIE         0x0040                 /* Receive Interrupt Enable */
+#define DZ_MSE         0x0020                 /* Master Scan Enable */
+#define DZ_CLR         0x0010                 /* Master reset */
+#define DZ_MAINT       0x0008                 /* Loop Back Mode */
+
+/*
+ * Definitions for the Receiver Buffer Register.
+ */
+#define DZ_RBUF_MASK   0x00FF                 /* Data Mask */
+#define DZ_LINE_MASK   0x0300                 /* Line Mask */
+#define DZ_DVAL        0x8000                 /* Valid Data indicator */
+#define DZ_OERR        0x4000                 /* Overrun error indicator */
+#define DZ_FERR        0x2000                 /* Frame error indicator */
+#define DZ_PERR        0x1000                 /* Parity error indicator */
+
+#define DZ_BREAK       0x0800                 /* BREAK event software flag */
+
+#define LINE(x) ((x & DZ_LINE_MASK) >> 8)     /* Get the line number
+                                                 from the input buffer */
+#define UCHAR(x) ((unsigned char)(x & DZ_RBUF_MASK))
+
+/*
+ * Definitions for the Transmit Control Register.
+ */
+#define DZ_LINE_KEYBOARD 0x0001
+#define DZ_LINE_MOUSE    0x0002
+#define DZ_LINE_MODEM    0x0004
+#define DZ_LINE_PRINTER  0x0008
+
+#define DZ_MODEM_RTS     0x0800               /* RTS for the modem line (2) */
+#define DZ_MODEM_DTR     0x0400               /* DTR for the modem line (2) */
+#define DZ_PRINT_RTS     0x0200               /* RTS for the prntr line (3) */
+#define DZ_PRINT_DTR     0x0100               /* DTR for the prntr line (3) */
+#define DZ_LNENB         0x000f               /* Transmitter Line Enable */
+
+/*
+ * Definitions for the Modem Status Register.
+ */
+#define DZ_MODEM_RI      0x0800               /* RI for the modem line (2) */
+#define DZ_MODEM_CD      0x0400               /* CD for the modem line (2) */
+#define DZ_MODEM_DSR     0x0200               /* DSR for the modem line (2) */
+#define DZ_MODEM_CTS     0x0100               /* CTS for the modem line (2) */
+#define DZ_PRINT_RI      0x0008               /* RI for the printer line (3) */
+#define DZ_PRINT_CD      0x0004               /* CD for the printer line (3) */
+#define DZ_PRINT_DSR     0x0002               /* DSR for the prntr line (3) */
+#define DZ_PRINT_CTS     0x0001               /* CTS for the prntr line (3) */
+
+/*
+ * Definitions for the Transmit Data Register.
+ */
+#define DZ_BRK0          0x0100               /* Break assertion for line 0 */
+#define DZ_BRK1          0x0200               /* Break assertion for line 1 */
+#define DZ_BRK2          0x0400               /* Break assertion for line 2 */
+#define DZ_BRK3          0x0800               /* Break assertion for line 3 */
+
+/*
+ * Definitions for the Line Parameter Register.
+ */
+#define DZ_KEYBOARD      0x0000               /* line 0 = keyboard */
+#define DZ_MOUSE         0x0001               /* line 1 = mouse */
+#define DZ_MODEM         0x0002               /* line 2 = modem */
+#define DZ_PRINTER       0x0003               /* line 3 = printer */
+
+#define DZ_CSIZE         0x0018               /* Number of bits per byte (mask) */
+#define DZ_CS5           0x0000               /* 5 bits per byte */
+#define DZ_CS6           0x0008               /* 6 bits per byte */
+#define DZ_CS7           0x0010               /* 7 bits per byte */
+#define DZ_CS8           0x0018               /* 8 bits per byte */
+
+#define DZ_CSTOPB        0x0020               /* 2 stop bits instead of one */ 
+
+#define DZ_PARENB        0x0040               /* Parity enable */
+#define DZ_PARODD        0x0080               /* Odd parity instead of even */
+
+#define DZ_CBAUD         0x0E00               /* Baud Rate (mask) */
+#define DZ_B50           0x0000
+#define DZ_B75           0x0100
+#define DZ_B110          0x0200
+#define DZ_B134          0x0300
+#define DZ_B150          0x0400
+#define DZ_B300          0x0500
+#define DZ_B600          0x0600
+#define DZ_B1200         0x0700 
+#define DZ_B1800         0x0800
+#define DZ_B2000         0x0900
+#define DZ_B2400         0x0A00
+#define DZ_B3600         0x0B00
+#define DZ_B4800         0x0C00
+#define DZ_B7200         0x0D00
+#define DZ_B9600         0x0E00
+
+#define DZ_RXENAB        0x1000               /* Receiver Enable */
+
+/*
+ * Addresses for the DZ registers
+ */
+#define DZ_CSR       0x00            /* Control and Status Register */
+#define DZ_RBUF      0x08            /* Receive Buffer */
+#define DZ_LPR       0x08            /* Line Parameters Register */
+#define DZ_TCR       0x10            /* Transmitter Control Register */
+#define DZ_MSR       0x18            /* Modem Status Register */
+#define DZ_TDR       0x18            /* Transmit Data Register */
+
+#define DZ_NB_PORT 4
+
+#define DZ_XMIT_SIZE   4096                 /* buffer size */
+#define DZ_WAKEUP_CHARS   DZ_XMIT_SIZE/4
+
+#endif /* DZ_SERIAL_H */