[PATCH 3/3] utils: Deprecate inexact fractional suffix sizes

[Eric Blake]

On 2/4/21 1:07 PM, Eric Blake wrote:
> The value '1.1k' is inexact; 1126.4 bytes is not possible, so we
> happen to truncate it to 1126.  Our use of fractional sizes is
> intended for convenience, but when a user specifies a fraction that is
> not a clean translation to binary, truncating/rounding behind their
> backs can cause confusion.  Better is to deprecate inexact values,
> which still leaves '1.5k' as valid, but alerts the user to spell out
> their values as a precise byte number in cases where they are
> currently being rounded.

And I promptly forgot to save my changes in my editor.  Consider this
squashed in:

diff --git i/docs/system/deprecated.rst w/docs/system/deprecated.rst
index c404c3926e6f..8e5e05a10642 100644
--- i/docs/system/deprecated.rst
+++ w/docs/system/deprecated.rst
@@ -154,6 +154,15 @@ Input parameters that take a size value should only
use a size suffix
 the value is hexadecimal.  That is, '0x20M' is deprecated, and should
 be written either as '32M' or as '0x2000000'.

+inexact sizes via scaled fractions (since 6.0)
+''''''''''''''''''''''''''''''''''''''''''''''
+
+Input parameters that take a size value should only use a fractional
+size (such as '1.5M') that will result in an exact byte value.  The
+use of inexact values (such as '1.1M') that require truncation or
+rounding is deprecated, and you should instead consider writing your
+unusual size in bytes (here, '1153433' or '1153434' as desired).
+
 QEMU Machine Protocol (QMP) commands
 ------------------------------------



-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org