tree cd62c595693dc7dc4c8886566145b19a8eecca79
parent 65a10cb163cddad099d663022a24e476fcfb22f3
author Linus Torvalds <torvalds@linux-foundation.org> 1611005490 -0800
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1614854256 +0100

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

[ 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>