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change semantics of ldisc ->compat_ioctl()

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First of all, make it return int.  Returning long when native method
had never allowed that is ridiculous and inconvenient.

More importantly, change the caller; if ldisc ->compat_ioctl() is NULL
or returns -ENOIOCTLCMD, tty_compat_ioctl() will try to feed cmd and
compat_ptr(arg) to ldisc's native ->ioctl().

That simplifies ->compat_ioctl() instances quite a bit - they only
need to deal with ioctls that are neither generic tty ones (those
would get shunted off to tty_ioctl()) nor simple compat pointer ones.

Note that something like TCFLSH won't reach ->compat_ioctl(),
even if ldisc ->ioctl() does handle it - it will be recognized
earlier and passed to tty_ioctl() (and ultimately - ldisc ->ioctl()).

For many ldiscs it means that NULL ->compat_ioctl() does the
right thing.  Those where it won't serve (see e.g. n_r3964.c) are
also easily dealt with - we need to handle the numeric-argument
ioctls (calling the native instance) and, if such would exist,
the ioctls that need layout conversion, etc.

All in-tree ldiscs dealt with.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2018-09-13 22:12:15 -04:00
parent 7ee3296551
commit f0193d3ea7
11 changed files with 36 additions and 100 deletions
Download patch file Download diff file Expand all files Collapse all files

10
include/linux/tty_ldisc.h
View file

@ -54,11 +54,17 @@
* low-level driver can "grab" an ioctl request before the line
* discpline has a chance to see it.
*
* long (*compat_ioctl)(struct tty_struct * tty, struct file * file,
* int (*compat_ioctl)(struct tty_struct * tty, struct file * file,
* unsigned int cmd, unsigned long arg);
*
* Process ioctl calls from 32-bit process on 64-bit system
*
* NOTE: only ioctls that are neither "pointer to compatible
* structure" nor tty-generic. Something private that takes
* an integer or a pointer to wordsize-sensitive structure
* belongs here, but most of ldiscs will happily leave
* it NULL.
*
* void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
*
* This function notifies the line discpline that a change has
@ -184,7 +190,7 @@ struct tty_ldisc_ops {
const unsigned char *buf, size_t nr);
int (*ioctl)(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg);
long (*compat_ioctl)(struct tty_struct *tty, struct file *file,
int (*compat_ioctl)(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg);
void (*set_termios)(struct tty_struct *tty, struct ktermios *old);
__poll_t (*poll)(struct tty_struct *, struct file *,