On Tue, Jun 05, 2018 at 04:05:38PM +0200, Andrea Bolognani wrote: > On Mon, 2018-06-04 at 11:33 +1000, David Gibson wrote: > > On Thu, May 24, 2018 at 07:34:25AM +0200, Peter Krempa wrote: > > > On Wed, May 23, 2018 at 19:09:59 +0200, Andrea Bolognani wrote: > > > > To be fair, it would perhaps make sense to perform the conversion > > > > directly inside QEMU, in order to make it more convenient not only > > > > for libvirt but for for people driving it directly as well. > > > > > > If strictly only powers of two make sense for this knob then this gives > > > you input validation for free. On the other hand, specifying a big > > > number can overflow internally if it is ever used in the non-exponent > > > form. I think the format does not matter much, since libvirt's job is to > > > shield users from such weirdness. > > > > Yeah, the above is basically my reasoning for using the exponent, not > > the final page size. > > As Peter mentioned, what format is used doesn't matter much from > libvirt's point of view, and in fact this RFC already implements > the necessary format conversion; however, it might be convenient > for people spawning QEMU directly to be able to specify the page > size in a more human-friendly format. > > How do you feel about that? If that's off the table, we'll just > go ahead with the current implementation. So, I need to keep the internal representation as a shift, since we only have 8 bits in the capability field. But that doesn't prevent changing the command line representation, since we could convert in the getter/setter functions. Personally I think the shift is *more* usable than a raw page size, since the latter is inevitably going to involve counting a bunch of zeroes to see if it's the number you meant. Allowing forms like "16M" / "16G" could be nicer; not sure if we have existing helper functions which will make that easy. TBH, if the user is already thinking about page sizes at this low level, I don't think doing it by shift is much of a stretch. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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