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Re: [PATCH] linux: add support for uname26 personality


On 2015-12-04 15:21, Florian Weimer wrote:
> On 12/03/2015 09:32 PM, Aurelien Jarno wrote:
> 
> >>> +/* When the kernel is running under the uname26 personality (for programs
> >>> +   that cannot handle "Linux 3.0"), it maps version 3.x to 2.6.40+x and
> >>> +   4.x to 2.6.60+x.  We need to convert that back to the standard version
> >>> +   numbering to be able to compare versions.  */
> >>> +static int
> >>> +convert_from_uname26 (int version)
> >>> +{
> >>> +  if ((version & 0xffff00) == 0x020600)
> >>> +    {
> >>> +      /* 2.6.40+x to 3.x */
> >>> +      if ((version & 0xff) >= 60)
> >>> +	version += 0x020000 - 60;
> >>> +      /* 2.6.60+x to 4.x */
> >>> +      else if ((version & 0xff) >= 40)
> >>> +	version += 0x010000 - 40;
> >>> +    }
> >>> +
> >>> +  return version;
> >>> +}
> >>
> >> â this function will have to be changed again for Linux 5.0.
> >>
> >> A long-term solution would map the minimum required version hard-coded
> >> into libc to its 2.6 equivalent, and check that if the kernel reports a
> >> 2.6 version.  This is solves the forward compatibility issue because the
> >> 2.6 mapping for the minimum version is known at the time glibc is compiled.
> > 
> > So you mean that we should have for example two defines in our code, one
> > for the standard version and the other for the 2.6 version and that both
> > would be defined at compilation time. Correct?
> 
> Essentially, yes.
> 
> > That still means we need to do the conversion at compile time to be able
> > to define both values.
> 
> Or you could write the inverse function convert_from_uname26 as an
> inline function or macro, and apply it to the (constant) minimum
> version.  I don't have a preference in either direction.

But then this function will have to be changed again for Linux 5.0â
Which is exactly your argument against the above code.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net


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