Date: Fri, 24 Dec 2004 14:53:45 +0100 From: "Norbert Koch" <nkoch@gmx.com> To: <freebsd-hackers@freebsd.org> Subject: parameters for tsleep(9) Message-ID: <000a01c4e9bf$fc7e56a0$fe78a8c0@k62300>
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Hello.
I am just writing a device driver for the i82527 (can-bus) chip.
For testing I need the driver to poll the chip instead of running
in interrupt mode.
My dev_t read function basically looks like this:
for (;;)
{
while (chip_has_data(...))
{
read_chip_data(...);
error = do_uiomove(...);
if (error || enough_read(...))
{
return error;
}
};
if (do_not_block_on_read(...))
{
return EWOULDBLOCK;
}
error = tsleep (XXX, PCATCH|PWAIT, "canrd", hz / 10);
if (error != EWOULDBLOCK)
{
return error;
}
}
XXX should be 'something' which could be used
as parameter to wakeup(9), I read in tsleep(9).
In the kernel source tree I found one
place where tsleep _only_ sleeps: in sys/isa/ppc.c
(which already seems to be in the attic [?] but
still is in my computer's source tree).
Here, the first parameter was set to NULL.
Doing this I found, that tsleep immediately
returns 0 (which means: wakueup was called)
_without_ waiting. I even crashed or
froze the kernel by calling tsleep (NULL, ...)
for a random number of times. After changing
this to the address of the read-function itself,
all worked fine. No more crashes.
Just for my understanding: Is this a bug?
Does the first parameter have to point to
something useful?
Is it allowed to point it to a code position?
Or should I use some kind of dummy data in
the softc structure instead?
What about the second parameter: Is PWAIT
ok here or should I use PZERO or whatever?
(And btw, why has ppc.c been removed?)
Thank you.
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