Re: [Qemu-devel] [PATCH] ide-test: fix failure for test_flush

[mdroth <mdroth@linux.vnet.ibm.com>]

On Tue, Jun 11, 2013 at 12:05:20PM +0200, Andreas Färber wrote:
> Am 10.06.2013 20:23, schrieb Michael Roth:
> > bd07684aacfb61668ae2c25b7dd00b64f3d7c7f3 added a test to ensure BSY
> > flag is set when a flush request is in flight. It does this by setting
> > a blkdebug breakpoint on flush_to_os before issuing a CMD_FLUSH_CACHE.
> > It then resumes CMD_FLUSH_CACHE operation and checks that BSY is unset.
> > 
> > The actual unsetting of BSY does not occur until ide_flush_cb gets
> > called in a bh, however, so in some cases this check will race with
> > the actual completion.
> > 
> > Fix this by polling the ide status register until BSY flag gets unset
> > before we do our final sanity checks. According to
> > f68ec8379e88502b4841a110c070e9b118d3151c this is in line with how a guest
> > would determine whether or not the device is still busy.
> > 
> > Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> > ---
> >  tests/ide-test.c |    5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tests/ide-test.c b/tests/ide-test.c
> > index 828e71a..7e2eb94 100644
> > --- a/tests/ide-test.c
> > +++ b/tests/ide-test.c
> > @@ -455,7 +455,10 @@ static void test_flush(void)
> >      data = inb(IDE_BASE + reg_device);
> >      g_assert_cmpint(data & DEV, ==, 0);
> >  
> > -    data = inb(IDE_BASE + reg_status);
> > +    do {
> > +        data = inb(IDE_BASE + reg_status);
> > +    } while (data & BSY);
> 
> Is a busy loop really a good idea for a qtest? CC'ing Anthony.

I'm not sure, my main justification was simply that we currently do it
in ide-test for send_dma_request()

> For the theoretical case that BSY is not cleared it might be better to
> terminate the loop with some timeout to get an assertion failure or at
> least use some form of sleep() to yield the thread while waiting?
> 

I don't think yielding/sleeping is too big a deal since we do a blocking
read() on each iteration which i assume will result in a yield while the
inb is being processed by qemu. Timeouts might be nice thing to add later
though. What about something like this?

inb_wait(addr, testfn, opaque, timeout) {
    while (timeout == -1 || timeout-- > 0) {
        val = inb(addr);
        if (testfn(val, opaque)) {
            return val;
        }
        usleep(1000);
    }
    abort()
}

It's not particularly precise, but for imposing a rough limit it should
work.

> > +
> >      assert_bit_set(data, DRDY);
> >      assert_bit_clear(data, BSY | DF | ERR | DRQ);
> 
> This BSY clear assertion will always be true now due to the above while
> condition; it won't if we change it though.
> 
> Regards,
> Andreas
> 
> >  
> 
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