Re: Memory mapped files question

[Chris Friesen <cfriesen@nortelnetworks.com>]

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



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