On Wed, Jun 09, 2021 at 08:46:22AM -0700, Richard Henderson wrote:
> On 6/8/21 1:20 PM, Daniel P. Berrangé wrote:
> > On Tue, Jun 08, 2021 at 12:45:51PM -0700, Richard Henderson wrote:
> > > On 6/8/21 4:22 AM, Paolo Bonzini wrote:
> > > > +pam = not_found
> > > > +if not get_option('auth_pam').auto() or have_system
> > > > + pam = cc.find_library('pam', has_headers: ['security/pam_appl.h'],
> > >
> > > The condition doesn't look right.
> > > Why are we looking for pam if --disable-pam-auth?
> > >
> > > Surely
> > >
> > > if not get_option('auth_pam').disabled() and have_system
> >
> > This isn't entirely obvious at first glance, but the line after
> > the one you quote with the 'required' param makes it "do the
> > right thing (tm)".
> >
> > The 'auth_pam' option is a tri-state taking 'enabled', 'disabled'
> > and 'auto', with 'auto' being the default state. When a tri-state
> > value is passed as the value of the 'required' parameter, then
> >
> > required==enabled is interpreted as 'required=true'
> > required==auto is interpreted as 'required=false'
> > required==disabled means the entire call is a no-op
> >
> > So this logic:
> >
> > if not get_option('auth_pam').auto() or have_system
> > pam = cc.find_library('pam', has_headers: ['security/pam_appl.h'],
> > required: get_option('auth_pam'),
> > ...)
> >
> > Means
> >
> > => If 'auto' is set, then only look for the library if we're
> > building system emulators. In this case 'required:' will
> > evaluate to 'false', and so we'll gracefully degrade
> > if the library is missing.
>
> If not have_system, there's no point in looking for pam *at all* regardless
> of get_option().
In theory we can simplify to
if have_system
pam = cc.find_library('pam', has_headers: ['security/pam_appl.h'],
required: get_option('auth_pam'),
...)
and this will be fine for builds with system emulators. The only
caveat is that if someone disables system emulators while also
passing -Dpam=enabled, we won't check for pam. That is a
nonsense combination of course, so probably doesn't matter
>
> > => If 'disabled' is set, then the 'find_library' call
> > will not look for anything, immediately return a
> > 'not found' result and let the caller carry on.
>
> This is not true. If 'required: false', find_library *will* look for the
> library, but it will allow it to be missing.
feature==disabled does not map to required: false
https://mesonbuild.com/Build-options.html#features
[quote]
enabled is the same as passing required : true.
auto is the same as passing required : false.
disabled do not look for the dependency and always return 'not-found'.
[/quote]
Regards,
Daniel
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