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From: "Norbert Koch" <nkoch@gmx.com>
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Subject: parameters for tsleep(9)
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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.