Re: FIBMAP ioctl restrictions: why?

Alan Cox (alan@lxorguk.ukuu.org.uk)
Mon, 8 Nov 1999 00:59:22 +0000 (GMT)


> to GDBM) and I want to sort file accesses before feeding them to the kernel,
> so that they will be executed in linear sector order and seek time will be
> minimized. Unfortunately, this plan breaks on the FIBMAP ioctl requiring
> CAP_SYS_RAWIO capability. To be honest, I don't see why -- can the kernel
> gurus advise me what deep reasons are behind this restriction?

Well firstly you should think very hard before trying this because most
operations will be filled from cache and many file systems dont have
constant block numbering - NFS for example. Block numbers may also be in
a logical not physical space so not relate to the media.

To answer the detail question. Several parts of the linux system do
insufficient checking for FIBMAP currently to be user accessible.

Alan

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