Messages in this thread | | | Date | Wed, 10 Nov 1999 20:33:54 +0100 | From | Jamie Lokier <> | Subject | Re: FIBMAP ioctl restrictions: why? |
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Alan Cox wrote: > > While we're here, I would like to request FIBMAP on directories, thanks. > > Just fix all of the race conditions with ftruncate, the sanity checking > and other missing map checks in the fs layers and send me a diff 8)
The result of FIBMAP can always be out of date by the time it reaches user space. So you can only use it as a hint for optimising read order, or like Lilo, you have to assume the underlying file is not being changed.
If you use it as a hint there's no big deal if the information is occasionally wrong due to a race. Are there any real race conditions with FIBMAP that cause real problems?
(It's not a great hint for a lot of reasons. One of them is the filesystem's tendancy to read ahead in a file, which tends to break your carefully planned read sequence...)
-- Jamie
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