From dd05add7b2b6004c5fa3a1f276f56d8668f86b65 Mon Sep 17 00:00:00 2001 From: Paulo Alcantara Date: Sat, 26 Sep 2026 19:20:30 -0300 Subject: netfs: zero the tail of a short DIO/unbuffered read 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 Reviewed-by: Namjae Jeon Signed-off-by: Paulo Alcantara Cc: Christian Brauner Cc: Matthew Wilcox Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: Bharath SM Cc: stable@vger.kernel.org --- drivers/tty/ttynull.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 110 insertions(+) create mode 100644 drivers/tty/ttynull.c (limited to 'drivers/tty/ttynull.c') diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c new file mode 100644 index 000000000..6b2f7208b --- /dev/null +++ b/drivers/tty/ttynull.c @@ -0,0 +1,110 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2019 Axis Communications AB + * + * Based on ttyprintk.c: + * Copyright (C) 2010 Samo Pogacnik + */ + +#include +#include +#include + +static const struct tty_port_operations ttynull_port_ops; +static struct tty_driver *ttynull_driver; +static struct tty_port ttynull_port; + +static int ttynull_open(struct tty_struct *tty, struct file *filp) +{ + return tty_port_open(&ttynull_port, tty, filp); +} + +static void ttynull_close(struct tty_struct *tty, struct file *filp) +{ + tty_port_close(&ttynull_port, tty, filp); +} + +static void ttynull_hangup(struct tty_struct *tty) +{ + tty_port_hangup(&ttynull_port); +} + +static ssize_t ttynull_write(struct tty_struct *tty, const u8 *buf, + size_t count) +{ + return count; +} + +static unsigned int ttynull_write_room(struct tty_struct *tty) +{ + return 65536; +} + +static const struct tty_operations ttynull_ops = { + .open = ttynull_open, + .close = ttynull_close, + .hangup = ttynull_hangup, + .write = ttynull_write, + .write_room = ttynull_write_room, +}; + +static struct tty_driver *ttynull_device(struct console *c, int *index) +{ + *index = 0; + return ttynull_driver; +} + +static struct console ttynull_console = { + .name = "ttynull", + .device = ttynull_device, +}; + +static int __init ttynull_init(void) +{ + struct tty_driver *driver; + int ret; + + driver = tty_alloc_driver(1, + TTY_DRIVER_RESET_TERMIOS | + TTY_DRIVER_REAL_RAW | + TTY_DRIVER_UNNUMBERED_NODE); + if (IS_ERR(driver)) + return PTR_ERR(driver); + + tty_port_init(&ttynull_port); + ttynull_port.ops = &ttynull_port_ops; + + driver->driver_name = "ttynull"; + driver->name = "ttynull"; + driver->type = TTY_DRIVER_TYPE_CONSOLE; + driver->init_termios = tty_std_termios; + driver->init_termios.c_oflag = OPOST | OCRNL | ONOCR | ONLRET; + tty_set_operations(driver, &ttynull_ops); + tty_port_link_device(&ttynull_port, driver, 0); + + ret = tty_register_driver(driver); + if (ret < 0) { + tty_driver_kref_put(driver); + tty_port_destroy(&ttynull_port); + return ret; + } + + ttynull_driver = driver; + register_console(&ttynull_console); + + return 0; +} + +static void __exit ttynull_exit(void) +{ + unregister_console(&ttynull_console); + tty_unregister_driver(ttynull_driver); + tty_driver_kref_put(ttynull_driver); + tty_port_destroy(&ttynull_port); +} + +module_init(ttynull_init); +module_exit(ttynull_exit); + +MODULE_DESCRIPTION("NULL TTY driver"); +MODULE_LICENSE("GPL v2"); -- cgit v1.3.1