I seem to have run into a problem which people have been
pointing out for years, but never gets fixed.
In tty_driver.h, the low-level driver routine wait_until_set()
function takes an "int" as a timeout value:
192 struct tty_operations {
193 int (*open)(struct tty_struct * tty, struct file * filp);
[...]
214 void (*wait_until_sent)(struct tty_struct *tty, int timeout);
[...]
228 };
But, in tty_ioclt.c in the tty_wait_unti_sent() function, the
timeout is a "long":
98 void tty_wait_until_sent(struct tty_struct *tty, long timeout)
99 {
100 #ifdef TTY_DEBUG_WAIT_UNTIL_SENT
101 char buf[64];
102
103 printk(KERN_DEBUG "%s wait until sent...\n", tty_name(tty, buf));
104 #endif
105 if (!timeout)
106 timeout = MAX_SCHEDULE_TIMEOUT;
107 if (wait_event_interruptible_timeout(tty->write_wait,
108 !tty_chars_in_buffer(tty), timeout) >= 0) {
109 if (tty->ops->wait_until_sent)
110 tty->ops->wait_until_sent(tty, timeout);
111 }
112 }
113 EXPORT_SYMBOL(tty_wait_until_sent);
This is fine on 32-bit systems, where "int" and "long" are
equivalent, but it results in breakage on 64-bit systems. At
line 106, timeout is set to MAX_SCHEDULE_TIMEOUT which is
7fffffffffffffff. When that value is passed to the low-level
driver routine at line 110, it gets truncated to ffffffff --
which is -1. That means that waiting until (jiffies+timeout)
returns immediately when the caller's intent was to wait as
long as possible.
People have been pointing out that type mismatch for many years
now. What's the justification for the low-level driver routine
parameter being "int" instead of "long"?
Since this doesn't seem to be something that's going to be
fixed, I guess a work-around for those of us who maintain
serial drivers is to treat a timeout of -1 as a special value
that means "forever"? Is that the intent?
--
Grant Edwards grante Yow! I feel like a wet
at parking meter on Darvon!
visi.com
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