Re: [PATCH] ip2: fix compile warnings

From: Randy.Dunlap
Date: Mon Dec 20 2004 - 02:59:47 EST

Jim Nelson wrote:
Randy.Dunlap wrote:

james4765@xxxxxxxxxxx wrote:

This fixes the following compile errors in the ip2 and ip2main drivers:

CC drivers/char/ip2main.o
drivers/char/ip2main.c:470: warning: initialization from incompatible pointer type

diff -urN --exclude='*~' linux-2.6.10-rc3-mm1-original/drivers/char/ip2main.c linux-2.6.10-rc3-mm1/drivers/char/ip2main.c
--- linux-2.6.10-rc3-mm1-original/drivers/char/ip2main.c 2004-12-03 16:55:03.000000000 -0500
+++ linux-2.6.10-rc3-mm1/drivers/char/ip2main.c 2004-12-17 16:24:24.094730049 -0500
@@ -467,7 +466,7 @@
static struct tty_operations ip2_ops = {
.open = ip2_open,
.close = ip2_close,
- .write = ip2_write,
+ .write = (void *) ip2_write,
.put_char = ip2_putchar,
.flush_chars = ip2_flush_chars,
.write_room = ip2_write_room,

The write() prototype in tty_operations is:
int (*write)(struct tty_struct * tty,
const unsigned char *buf, int count);

Somehow the cast does eliminate the compiler warning (and give
a false sense of correctness).

However, ip2main.c::ip2_write() should be modified like so:

static int
ip2_write( PTTY tty, const unsigned char *pData, int count)

and drop the cast and fix the ip2_write comment (drop old arg 2),
and fix the ip2_write() prototype.
But then you (someone) will have to decide how to handle the
dropped <user> parameter when calling i2Output()...
I don't know the answer to that.
I just changed <user> to 0 to get a clean build of ip2main.o,
but ip2/i2lib.c still needs some work.

Sorry for the constant n00b questions, but:

Is there anything outside the kernel that could call tty_operations.write?

Sorry, I don't know the path to get to that code.

drivers/input/serio/serport.c uses: (as an example)

static int serport_serio_write(struct serio *serio, unsigned char data)
struct serport *serport = serio->port_data;
return -(serport->tty->driver->write(serport->tty, &data, 1) != 1);

I'm guessing that something does copy_from_user() before tty_operations.write is called, but I don't know quite what that is.

Can anyone to point me in the direction of where the user/kernel interface for tty devices is?

Given the way this is set up -

int (*write)(struct tty_struct * tty, const unsigned char *buf, int count);


ip2_write( PTTY tty, int user, const unsigned char *pData, int count)

I don't even know if the driver would work - I think you'd have serious problems as it tries to dereference a pointer that is half-integer.

I didn't quite get the "half-integer" part...
Unless you mean that the function interface is just broken.
Yes, it is.

Am I reading this wrong?

It looks to me like the Kconfig entry for CONFIG_COMPUTONE
should just use BROKEN instead of BROKEN_ON_SMP since its
.write function interface hasn't been updated.

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