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3b830a9c34
The tty line discipline .read() function was passed the final user pointer destination as an argument, which doesn't match the 'write()' function, and makes it very inconvenient to do a splice method for ttys. This is a conversion to use a kernel buffer instead. NOTE! It does this by passing the tty line discipline ->read() function an additional "cookie" to fill in, and an offset into the cookie data. The line discipline can fill in the cookie data with its own private information, and then the reader will repeat the read until either the cookie is cleared or it runs out of data. The only real user of this is N_HDLC, which can use this to handle big packets, even if the kernel buffer is smaller than the whole packet. Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
69 lines
1.3 KiB
C
69 lines
1.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/types.h>
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#include <linux/errno.h>
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#include <linux/tty.h>
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#include <linux/module.h>
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/*
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* n_null.c - Null line discipline used in the failure path
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*
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* Copyright (C) Intel 2017
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*/
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static int n_null_open(struct tty_struct *tty)
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{
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return 0;
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}
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static void n_null_close(struct tty_struct *tty)
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{
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}
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static ssize_t n_null_read(struct tty_struct *tty, struct file *file,
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unsigned char *buf, size_t nr,
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void **cookie, unsigned long offset)
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{
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return -EOPNOTSUPP;
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}
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static ssize_t n_null_write(struct tty_struct *tty, struct file *file,
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const unsigned char *buf, size_t nr)
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{
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return -EOPNOTSUPP;
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}
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static void n_null_receivebuf(struct tty_struct *tty,
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const unsigned char *cp, char *fp,
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int cnt)
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{
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}
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static struct tty_ldisc_ops null_ldisc = {
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.owner = THIS_MODULE,
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.magic = TTY_LDISC_MAGIC,
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.name = "n_null",
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.open = n_null_open,
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.close = n_null_close,
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.read = n_null_read,
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.write = n_null_write,
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.receive_buf = n_null_receivebuf
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};
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static int __init n_null_init(void)
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{
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BUG_ON(tty_register_ldisc(N_NULL, &null_ldisc));
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return 0;
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}
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static void __exit n_null_exit(void)
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{
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tty_unregister_ldisc(N_NULL);
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}
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module_init(n_null_init);
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module_exit(n_null_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Alan Cox");
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MODULE_ALIAS_LDISC(N_NULL);
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MODULE_DESCRIPTION("Null ldisc driver");
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