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tty: convert tty_ldisc_ops 'read()' function to take a kernel pointer

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[ Upstream commit 3b830a9c34d5897be07176ce4e6f2d75e2c8cfd7 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Linus Torvalds
2021-01-18 13:31:30 -08:00
committed by Greg Kroah-Hartman
parent 65a10cb163
commit 279e54536d
14 changed files with 178 additions and 102 deletions
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3
net/nfc/nci/uart.c
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@@ -292,7 +292,8 @@ static int nci_uart_tty_ioctl(struct tty_struct *tty, struct file *file,
/* We don't provide read/write/poll interface for user space. */
static ssize_t nci_uart_tty_read(struct tty_struct *tty, struct file *file,
unsigned char __user *buf, size_t nr)
unsigned char *buf, size_t nr,
void **cookie, unsigned long offset)
{
return 0;
}