Re: Memory mapped files question

Chris Friesen (cfriesen@nortelnetworks.com)
Mon, 14 Apr 2003 17:24:38 -0400

Alan Cox wrote:
> On Llu, 2003-04-14 at 20:42, Bryan Shumsky wrote:
>
>>Rewriting all of our code to manually handle the flushing is a MAJOR
>>undertaking, so I was hoping there might be some sneaky solution you could
>>come up with. Any ideas?
>>
>
> Create a thread that does msync's every so often. Its that simple

How do you deal with ensuring (or even trying to ensure) that the stuff *on
disk* is sane?

If I understand correctly, msync() doesn't guarantee order of writes, so
randomly firing off msync() calls doesn't help.

If I want to update an entry and then set a flag saying that the entry is
correct, I need to have two msyncs, one for the entry data, and one for the
flag. I had hoped that I could avoid this by opening the file with O_SYNC, but
hpa just disabused me of that notion...

Are the mmap semantics different for devices?

Chris

-- 
Chris Friesen                    | MailStop: 043/33/F10
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