diff options
| -rw-r--r-- | dev/multiarch/design.mdwn | 185 | ||||
| -rw-r--r-- | dev/todo/multiarch.mdwn | 81 |
2 files changed, 203 insertions, 63 deletions
diff --git a/dev/multiarch/design.mdwn b/dev/multiarch/design.mdwn new file mode 100644 index 0000000..fff2864 --- /dev/null +++ b/dev/multiarch/design.mdwn @@ -0,0 +1,185 @@ +[[!meta title="Multiarch Design"]] + +There are three high-level design aspects to this multiarch implementation: the +filesystem hierarchy that primarily enables package coinstallability, control +information documenting package coinstallability and dependency satisfaction, +and coinstallability considerations in package management. + +For reference, see the [specification][wuc-mas] and [other +documentation][wdo-ma] for multiarch in Debian and Ubuntu. + + +Filesystem Hierarchy +==================== + +For packages to be coninstallable with themselves (such that a user can have +multiple architecture builds of one package installed simultaneously), all +architecture-dependent files must be installed in architecture-dependent +locations. The most straightforward way to do this is to embed architecture +strings into filesystem paths. + +Debian and Ubuntu do something similar to this. In a Debian library package +that supports multiarch, shared object files are installed in +`/usr/lib/<triplet>`, where `<triplet>` is a [GNU system type][ac-systemtype]. + +The scope of Debian's and Ubuntu's multiarch work [does not include][wdo-ma-fut] +coinstallable executable programs. + +Such work, however, would help enable cross installation of packages. So a goal +of this multiarch implementation is to support coinstallation of shared object +files, header files, and executable programs. + +There are two proposed filesystem hierarchies (see below) to support this. + +Parts of the toolchain (especially the dynamic linker) need to be configured +and/or patched to use multiarch library paths. Additionally, at least the +native-architecture executable program directories have to be added to the PATH +environment variable. + +Proposal 1: `/usr` Organized Primarily by Architecture +------------------------------------------------------ + +It may be useful to install all architecture-dependent files under +`/usr/<arch>`, where `<arch>` is a distribution architecture string. The +filesystem hierarchy would then look something like this: + + / + +- bin/ + | +- core-linux-eglibc/ + | \- cortexa8-linux-eglibc/ + +- lib/ + | +- core-linux-eglibc/ + | \- cortexa8-linux-eglibc/ + +- sbin/ + | +- core-linux-eglibc/ + | \- cortexa8-linux-eglibc/ + \- usr/ + +- core-linux-eglibc/ + | +- bin/ + | +- games/ + | +- include/ + | +- lib/ + | +- sbin/ + +- cortexa8-linux-eglibc/ + | +- bin/ + | +- games/ + | +- include/ + | +- lib/ + | +- sbin/ + +- bin/ + +- games/ + +- include/ + +- local/ + +- sbin/ + +- share/ + \- src/ + +Note that `/usr/lib` doesn't exist, as no architecture-independent files should +be installed there. + +Proposal 2: `/usr` Organized Secondarily by Architecture +-------------------------------------------------------- + +It may be cleaner and slightly more efficient to install architecture-dependent +files within an architecture-dependent directory under otherwise standard paths. +This is similar to how Debian and Ubuntu have designed their multiarch +filesystem hierarchy. Such an organized filesystem hierarchy would look +something like this: + + / + +- bin/ + | +- core-linux-eglibc/ + | \- cortexa8-linux-eglibc/ + +- lib/ + | +- core-linux-eglibc/ + | \- cortexa8-linux-eglibc/ + +- sbin/ + | +- core-linux-eglibc/ + | \- cortexa8-linux-eglibc/ + \- usr/ + +- bin/ + +- core-linux-eglibc/ + +- cortexa8-linux-eglibc/ + +- games/ + +- core-linux-eglibc/ + +- cortexa8-linux-eglibc/ + +- include/ + +- core-linux-eglibc/ + +- cortexa8-linux-eglibc/ + +- lib/ + +- core-linux-eglibc/ + +- cortexa8-linux-eglibc/ + +- local/ + +- sbin/ + +- core-linux-eglibc/ + +- cortexa8-linux-eglibc/ + +- share/ + \- src/ + + +Control Information +=================== + +New package control information will be needed to indicate whether a package is +coinstallable with itself and to mark its purpose. + +During build-time, there are two possible architectures for any dependent package: + + * Host-architecture (architecture for which packages are built). Packages for + this architecture provide things like libraries and headers. An example is + libexpat.1-dev. + * Build-architecture (architecture on which packages are built). Packages for + this architecture provide things like build utilities An example is + pkg-config. + +During install-time, there are also two possible architectures for any dependent +package: + + * Host-architecture (architecture for which packages are installed). Packages + for this architecture provide things like libraries and utilities. Examples + include libz.1, gcc-4.7-<arch> (dependency of gcc-<arch>), and fakeroot + (recommendation of opkhelper-1.0). + * Install-architecture (architecture on which packages are installed). + Packages for this architecture provide things like utilities used by + maintainer scripts. An example is insserv (or a similar tool). + +Host-architecture packages should be coinstallable with themselves, and they +should satisfy dependencies of the same architecture. For example, the +dependency of libexpat.1-dev:cortexa8-linux-eglibc on libexpat.1 should resolve +to a dependency on libexpat.1:cortexa8-linux-eglibc. + +Build- and install-architecture packages need not be coinstallable with +themselves, and they should satisfy dependencies of any architecture. For +example, the build dependency of glib (built on core-linux-eglibc for +cortexa8-linux-eglibc) on pkg-config should resolve to a build dependency on +pkg-config:core-linux-eglibc. + +Debian and Ubuntu specify such properties in a `Multi-Arch` control field. A +value of `same` indicates that a package satisfies dependencies of the same +architecture; a value of `foreign` indicates that a package satisfies +dependencies of any architecture. We can implement something similar, perhaps +even using the same terminology. + +Logic to handle the new control information will need to be added to opkg and +opkhelper (specifically oh-checkbuilddeps). + +Special design considerations need to be given to install-time dependencies. +Specific use case analysis can help here. + + +Architecture-Independent Files +============================== + +Many packages provide architecture-independent files (configuration files, +documentation, data, etc.). To the extent possible and feasible, these should +simply be provided by architecture-independent packages (with names like +"*-common", "*-data", or "*-base"). + +If this is not possible in all cases, then some modifications to opkg will be +necessary (reference counting, implicit "Breaks" relationships, etc.). + + +[wdo-ma]: http://wiki.debian.org/Multiarch +[wuc-mas]: https://wiki.ubuntu.com/MultiarchSpec +[ac-systemtype]: https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/System-Type.html +[wdo-ma-fut]: http://wiki.debian.org/Multiarch#Future_development diff --git a/dev/todo/multiarch.mdwn b/dev/todo/multiarch.mdwn index 4bf5413..2f34940 100644 --- a/dev/todo/multiarch.mdwn +++ b/dev/todo/multiarch.mdwn @@ -1,77 +1,32 @@ [[!meta title="Multiarch"]] Multiarch refers to the ability to install and use packages built for non-native -architectures. It is currently being [documented and implemented][wdo-ma] in -Debian and Ubuntu. Multiarch is useful for this distribution because it makes -cross compiling easy (see "Package Cross Building Tool" and "Multiarch Cross -Toolchain Packages"). +architectures and the ability to coinstall multiple architecture builds of any +supporting package. -Simply speaking, there are six [aspects of a multiarch implementation][ma-des]: +It is currently being [designed][wuc-mas] and [implemented][wdo-ma] in Debian +and Ubuntu. Multiarch is useful for this distribution because it can make cross +building and cross installing easy. - * **Filesystem Hierarchy** - - To accomodate simultaneous installation of shared libraries built for - different architectures, library paths are suffixed with a directory name - that identifies a particular architecture. For this distribution, that - directory name will be the name of the binary architecture; for example, - library paths for the `cortexa8-linux-eglibc` architecture will be - `/lib/cortexa8-linux-eglibc` and `/usr/lib/cortexa8-linux-eglibc`. - - The toolchain (especially the dynamic linker) needs to be configured to use - these library paths. - * **A `Multi-Arch` Control Field** - - A `Multi-Arch` control field specifies how a package can satisfy - dependencies of other packages. A value of `same` means that a package can - only satisfy dependencies of packages built for the architecture for which - it was built. This is useful for shared libraries, which can only be - dynamically linked against binary objects built for the same architecture. - A value of `foreign` means that a package can satisfy dependencies of - packages built for any architecture. This is useful for utility programs, - which can be used by software built for any architecture. - - The package manager (opkg in our case) and package building tools - (specifically oh-checkbuilddeps of opkhelper) must be able to understand - and use this field in resolving package dependencies. +Design Aspects +============== - * **Architecture Specification in Package Relationships** - - Control fields like `Depends` are extended to support an architecture - specification of either `any` or `same`, allowing a package to specify - whether or not it needs a package of the same architecture. The dependent - package has a `Multi-Arch` field with value `allowed`. - - The package manager and package building tools must be able to understand - and use this architecture syntax in relationship fields. +There are three high-level design aspects to this multiarch implementation: the +filesystem hierarchy that primarily enables package coinstallability, control +information documenting package coinstallability and dependency satisfaction, +and coinstallability considerations in package management. - * **Handling of Packages with `Architecture: all`** - - Dependence on packages installable and usable on any architecture - (especially considering opkg's ability to install packages of multiple - architectures) must be researched. +For more details, see the [[multiarch_design_document|dev/multiarch/design]]. - * **Non-Library Files in Library Packages** - - Library packages provide files outside of system library paths, such as - configuration and package documentation files. A solution must be designed - to allow a package built for one architecture to be co-installable with the - same package built for a different architecture (or to determine if they are - co-installable at all). - * **Ability to Install Packages Built for Non-Native Architectures** - - The package manager must be able to install packages built for multiple - architectures (the whole point of multiarch). Fortunately for us, opkg - already handles this. The `arch` option in `opkg.conf` [allows the user to - specify architectures][opkg-conf-arch] for which packages can be installed. +Goals +===== -In summary, there is much design work to be done, opkg and opkhelper must be -modified to support multiarch, and certain packages will need to be built to -handle multiarch library paths. Of course Debian is a great reference -implementation, but there still remains much original work to be done. +The design and implementation of the filesystem hierarchy is +[[a_goal_for_release_1.0.0|dev/releases/1]]. Package coinstallability is not a +goal for this release. [wdo-ma]: http://wiki.debian.org/Multiarch -[ma-des]: https://wiki.ubuntu.com/MultiarchSpec#Design -[opkg-conf-arch]: http://wiki.openwrt.org/doc/techref/opkg#adjust.architectures +[wuc-mas]: https://wiki.ubuntu.com/MultiarchSpec |