Gentoo Archives: gentoo-dev

From: Ciaran McCreesh <ciaranm@g.o>
To: gentoo-dev@l.g.o
Subject: [gentoo-dev] use.mask and no* flags
Date: Mon, 27 Sep 2004 17:31:46
Message-Id: 20040927182758.3b03109e@snowdrop.home
1 Looks like some people aren't sure about how use.mask works, or why arch
2 developers tend to hate noblah USE flags... Hopefully this'll clear
3 things up.
5 Consider a hypothetical package named 'vplayer' which plays videos [1].
6 This package has optional support, via USE flags, for various sound and
7 video output modes, video codecs and so on.
9 One of vplayer's optional features is support for the 'fakemedia' codec,
10 which is unfortunately only available as a dodgy x86 binary. So how do
11 we handle this? We *could* do something like the following: >
13 RDEPEND="x86? ( fakemedia? ( >=media-libs/fakemedia-1.1 ) )"
15 < However, that's not really very nice -- what happens when an amd64
16 binary is made as well? Also, users on other archs will see the
17 fakemedia flag listed in emerge -pv output, even though it's not
18 actually available.
20 Or, from the other side... vplayer supports output via ALSA as one
21 option. Unfortunately, ALSA isn't available on sparc [2] or alpha. So,
22 you could do: >
24 DEPEND="!sparc? ( !alpha? ( media-libs/alsa-lib ) )"
26 < Again, this is messy, and alsa still shows up as an option in emerge
27 -pv. Also, when we get ALSA working on sparc, we'd have to go through
28 every single ebuild that does this and remove the !sparc? stuff.
30 The solution is use.mask. Each profile can have a use.mask file which
31 can be used to force certain USE flags to be disabled on a given arch
32 (or, for that matter, on, say, selinux systems or a particular subarch).
33 Say the'fakemedia' USE flag was masked on non-x86, the following would
34 be totally legal and wouldn't break anything: >
36 RDEPEND="fakemedia? ( >=media-libs/fakemedia-1-1 )"
38 < Anyone on a non-x86 box would see the following when doing emerge -pv
39 vplayer: >
41 [ebuild R ] media-video/vplayer-1.2 alsa -arts (-fakemedia)
43 < So, if you're thinking about doing an arch? DEPEND, please think
44 again. It's easy to get things added to use.mask, just file a bug or ask
45 the arch people on IRC. We'd much rather add a line into a couple of
46 textfiles than have to screw around with arch? flags. Really, the only
47 time you should be using arch? flags for *DEPEND [3] is when a
48 particular feature usually works on a given arch but doesn't for one
49 particular package (for example, maybe vplayer's opengl support is
50 broken on 64bit systems).
52 Now we get onto those pesky no* flags. Currently there is no way for us
53 to force a USE flag on on a given profile [4]. So, if you do something
54 like this: >
56 RDEPEND="!noalsa? ( media-libs/alsa )"
58 < you're screwing over those archs that don't have alsa support, and
59 there's nothing we can do about it short of those hideous arch? flags.
61 [1]: This isn't a dig at the mplayer guys, just that sound/video apps
62 are an easy example here :)
64 [2]: Well... Not entirely true... ALSA itself will mostly work on some
65 sparc boxes with a 2.6.x kernel, but the mixer hates our userland.
67 [3]: In other places it does of course have perfectly valid uses.
69 [4]: This may or may not be a portage deficiency. Point is, it's an
70 issue, and whilst complaining that portage needs to be fixed is a viable
71 long term solution, right now it's no use. Although if someone files a
72 bug requesting a use.force, please Cc: me.
74 --
75 Ciaran McCreesh : Gentoo Developer (Sparc, MIPS, Vim, Fluxbox)
76 Mail : ciaranm at
77 Web :


Subject Author
Re: [gentoo-dev] use.mask and no* flags Luke-Jr <luke-jr@×××××××.org>
Re: [gentoo-dev] use.mask and no* flags Mike Frysinger <vapier@g.o>