In message <20051114233622.GA12603@gurney.reilly.home>, Andrew Reilly writes:
>On Sun, Nov 13, 2005 at 07:49:38PM -0500, Steven M. Bellovin wrote:
>> It seems likely that nothing will make this work short of a real byte 
>> offset in d_off.  This in turn suggests that either the linux emulation 
>> layer has to have a way of knowing if it needs to do a conversion, or 
>> the file system layer needs to do the conversion, possibly as a result 
>> of a mount-time flag.  I'd really rather avoid the latter if possible 
>> -- how expensive would it be for tmpfs to maintain a real byte count?  
>> (Seeking to that point need not be cheap; it's an infrequent operation, 
>> I suspect.)
>
>Is it not possible to have the emulated lseek understand the
>opaque cookies (perhaps with a hash lookup) and do the right
>thing?

I haven't looked at the code, but I suspect that that doesn't work well 
-- when do you purge the table?  
>
>What is the good of passing an opaque cookie out to user-land if
>it's not subsequently useful for something?
>
Good question, unless it's the sort of cookie used by telldir()/
seekdir().


		--Steven M. Bellovin, http://www.cs.columbia.edu/~smb