Hi Jiaying, On 08/16/2011 07:53 AM, Jiaying Zhang wrote: > Hi Michael, > > On Mon, Aug 15, 2011 at 1:56 AM, Michael Tokarev <mjt@xxxxxxxxxx> wrote: >> 15.08.2011 12:00, Michael Tokarev wrote: >> [....] >> >> So, it looks like this (starting with cold cache): >> >> 1. rename the redologs and copy them over - this will >> make a hot copy of redologs >> 2. startup oracle - it will complain that the redologs aren't >> redologs, the header is corrupt >> 3. shut down oracle, start it up again - it will succeed. >> >> If between 1 and 2 you'll issue sync(1) everything will work. >> When shutting down, oracle calls fsync(), so that's like >> sync(1) again. >> >> If there will be some time between 1. and 2., everything >> will work too. >> >> Without dioread_nolock I can't trigger the problem no matter >> how I tried. >> >> >> A smaller test case. I used redo1.odf file (one of the >> redologs) as a test file, any will work. >> >> $ cp -p redo1.odf temp >> $ dd if=temp of=foo iflag=direct count=20 > Isn't this the expected behavior here? When doing > 'cp -p redo1.odf temp', data is copied to temp through > buffer write, but there is no guarantee when data will be > actually written to disk. Then with 'dd if=temp of=foo > iflag=direct count=20', data is read directly from disk. > Very likely, the written data hasn't been flushed to disk > yet so ext4 returns zero in this case. Sorry, but it doesn't sound correct to me. Say we use a buffer write to a file and then use direct i/o read, what we expect(or at least Michael expect) is that we use read the updated data, not the stale one. I thought of a tiny race window in ext4 here, but need to do some test to verify and then fix it. Thanks Tao -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
