Re: [Qemu-devel] [PATCH v9 2/9] include: Add a lookup table of sizes

[Leonid Bloch]

On 9/21/18 3:17 PM, Alberto Garcia wrote:
> On Tue 18 Sep 2018 05:29:16 PM CEST, Leonid Bloch wrote:
> > Adding a lookup table for the powers of two, with the appropriate size
> > prefixes. This is needed when a size has to be stringified, in which
> > case something like '(1 * KiB)' would become a literal '(1 * (1L <<
> > 10))' string. Powers of two are used very often for sizes, so such a
> > table will also make it easier and more intuitive to write them.
>
> I wonder in what cases you want to stringify those literals... if it's
> something that you want to show the user you either:
>
>    a) know the value in advance, and then you probably want to show
>       "4 GiB" instead of "4294967296 bytes"

Then the value will need to be set in two places at any future change.

>    b) don't know the value in advance (it's a variable), but then you
>       can't use these macros.
>
> Am I missing anything?

This is needed in some places:

$ ag 'stringify\(DEFAULT_CLUSTER_SIZE\)'
block/parallels.c
99:            .def_value_str = stringify(DEFAULT_CLUSTER_SIZE),

block/vdi.c
988:            .def_value_str = stringify(DEFAULT_CLUSTER_SIZE)

block/qcow2.c
4726:            .def_value_str = stringify(DEFAULT_CLUSTER_SIZE)

The latter causes failure in test case 137 if defined as (64 * KiB).

Of course the values in block/parallels.h and block/vdi.c will need to 
be changed as well, I'll do it in a separate patch.

Besides resolving the cases with the necessity to stringify, It also 
creates nice shortcuts for all feasible power-of-two sizes, which are 
very common.

Leonid.

> Berto