X-Git-Url: https://git.saurik.com/apt.git/blobdiff_plain/90bcac9e663d1a37eb2e0f1ba0878d0a545c9991..08fcf9628806af202e555bd02b3611e4e9a3d757:/doc/external-dependency-solver-protocol.txt diff --git a/doc/external-dependency-solver-protocol.txt b/doc/external-dependency-solver-protocol.txt index 8c13b185c..452212602 100644 --- a/doc/external-dependency-solver-protocol.txt +++ b/doc/external-dependency-solver-protocol.txt @@ -1,10 +1,18 @@ -# APT External Dependency Solver Protocol (EDSP) - version 0.3 +# APT External Dependency Solver Protocol (EDSP) - version 0.5 This document describes the communication protocol between APT and external dependency solvers. The protocol is called APT EDSP, for "APT External Dependency Solver Protocol". +## Terminology + +In the following we use the term **architecture qualified package name** +(or *arch-qualified package names* for short) to refer to package +identifiers of the form "package:arch" where "package" is a package name +and "arch" a dpkg architecture. + + ## Components - **APT**: we know this one. @@ -26,10 +34,12 @@ internal solver, is reserved, and cannot be used by external solvers. ## Installation -Each external solver is installed as a file under -`/usr/lib/apt/solvers`. The naming scheme is -`/usr/lib/apt/solvers/NAME`, where `NAME` is the name of the external -solver. +Each external solver is installed as a file under Dir::Bin::Solvers (see +below), which defaults to `/usr/lib/apt/solvers`. We will assume in the +remainder of this section that such a default value is in effect. + +The naming scheme is `/usr/lib/apt/solvers/NAME`, where `NAME` is the +name of the external solver. Each file under `/usr/lib/apt/solvers` corresponding to an external solver must be executable. @@ -45,17 +55,32 @@ Several APT options can be used to affect dependency solving in APT. An overview of them is given below. Please refer to proper APT configuration documentation for more, and more up to date, information. -- **APT::Solver::Name**: the name of the solver to be used for +- **APT::Solver**: the name of the solver to be used for dependency solving. Defaults to `internal` +- **Dir::Bin::Solvers**: absolute path of the directory where to look for + external solvers. Defaults to `/usr/lib/apt/solvers`. + - **APT::Solver::Strict-Pinning**: whether pinning must be strictly respected (as the internal solver does) or can be slightly deviated from. Defaults to `yes`. -- **APT::Solver::NAME::Preferences** (where NAME is a solver name): - solver-specific user preference string used during dependency solving, - when the solver NAME is in use. Check solver-specific documentation - for what is supported here. Defaults to the empty string. +- **APT::Solver::Preferences**: user preference string used during + dependency solving by the requested solver. Check the documentation + of the solver you are using if and what is supported as a value here. + Defaults to the empty string. + +- **APT::Solver::RunAsUser**: if APT itself is run as root it will + change to this user before executing the solver. Defaults to the value + of APT::Sandbox::User, which itself defaults to `_apt`. Can be + disabled by set this option to `root`. + +The options **Strict-Pinning** and **Preferences** can also be set for +a specific solver only via **APT::Solver::NAME::Strict-Pinning** and +**APT::Solver::NAME::Preferences** respectively where `NAME` is the name +of the external solver this option should apply to. These options if set +override the generic options; for simplicity the documentation will +refer only to the generic options. ## Protocol @@ -106,39 +131,56 @@ Within a dependency solving scenario, a request represents the action on installed packages requested by the user. A request is a single Deb 822 stanza opened by a mandatory Request field -and followed by a mixture of action and preference fields. +and followed by a mixture of action, preference, and global +configuration fields. The value of the **Request:** field is a string describing the EDSP protocol which will be used to communicate. At present, the string must -be `EDSP 0.3`. +be `EDSP 0.5`. Request fields are mainly used to identify the beginning +of a request stanza; their actual values are otherwise not used by the +EDSP protocol. + +The following **configuration fields** are supported in request stanzas: -a unique request identifier, such as an -UUID. Request fields are mainly used to identify the beginning of a -request stanza; their actual values are otherwise not used by the EDSP -protocol. +- **Architecture:** (mandatory) The name of the *native* architecture on + the user machine (see also: `dpkg --print-architecture`) + +- **Architectures:** (optional, defaults to the native architecture) A + space separated list of *all* architectures known to APT (this is + roughly equivalent to the union of `dpkg --print-architecture` and + `dpkg --print-foreign-architectures`) The following **action fields** are supported in request stanzas: - **Install:** (optional, defaults to the empty string) A space - separated list of package names, with *no version attached*, to - install. This field denotes a list of packages that the user wants to - install, usually via an APT `install` request. + separated list of arch-qualified package names, with *no version + attached*, to install. This field denotes a list of packages that the + user wants to install, usually via an APT `install` request. - **Remove:** (optional, defaults to the empty string) Same syntax of Install. This field denotes a list of packages that the user wants to remove, usually via APT `remove` or `purge` requests. -- **Upgrade:** (optional, defaults to `no`). Allowed values: `yes`, +- **Upgrade-All:** (optional, defaults to `no`). Allowed values `yes`, `no`. When set to `yes`, an upgrade of all installed packages has been - requested, usually via an APT `upgrade` request. - -- **Dist-Upgrade:** (optional, defaults to `no`). Allowed values: `yes`, - `no`. Same as Upgrade, but for APT `dist-upgrade` requests. + requested, usually via an upgrade command like 'apt full-upgrade'. - **Autoremove:** (optional, defaults to `no`). Allowed values: `yes`, `no`. When set to `yes`, a clean up of unused automatically installed packages has been requested, usually via an APT `autoremove` request. +- **Upgrade:** (deprecated, optional, defaults to `no`). Allowed values: + `yes`, `no`. When set to `yes`, an upgrade of all installed packages + has been requested, usually via an APT `upgrade` request. A value of + `yes` is equivalent to the fields `Upgrade-All`, + `Forbid-New-Install`and `Forbid-Remove` all set to `yes`. + +- **Dist-Upgrade:** (deprecated, optional, defaults to `no`). Allowed + values: `yes`, `no`. Same as Upgrade, but for APT `dist-upgrade` + requests. A value of `yes` is equivalent to the field `Upgrade-All` + set to `yes` and the fields `Forbid-New-Install`and `Forbid-Remove` + set to `no`. + The following **preference fields** are supported in request stanzas: - **Strict-Pinning:** (optional, defaults to `yes`). Allowed values: @@ -150,8 +192,21 @@ The following **preference fields** are supported in request stanzas: field comes from the `APT::Solver::Strict-Pinning` configuration option. -- **Preferences:** a solver-specific optimization string, usually coming - from the `APT::Solver::Preferences` configuration option. +- **Forbid-New-Install:* (optional, defaults to `no`). Allowed values: + `yes`, `no`. When set to `yes` the resolver is forbidden to install + new packages in its returned solution. + +- **Forbid-Remove:* (optional, defaults to `no`). Allowed values: `yes`, + `no`. When set to `yes` the resolver is forbidden to remove currently + installed packages in its returned solution. + +- **Solver:** (optional, defaults to the empty string) a purely + informational string specifying to which solver this request was send + initially. + +- **Preferences:** (optional, defaults to the empty string) + a solver-specific optimization string, usually coming from the + `APT::Solver::Preferences` configuration option. #### Package universe @@ -189,7 +244,7 @@ field. The following fields are supported in package stanzas: - **APT-Candidate:** (optional, defaults to `no`). Allowed values: `yes`, `no`. When set to `yes`, the corresponding package is the APT candidate for installation among all available packages with the same - name. + name and architecture. - **APT-Automatic:** (optional, defaults to `no`). Allowed values: `yes`, `no`. When set to `yes`, the corresponding package is marked by @@ -197,6 +252,22 @@ field. The following fields are supported in package stanzas: should be removed by the solver only when the Autoremove action is requested (see Request section). +- **APT-Release:** (optional) The releases the package belongs to, according to + APT. The format of this field is multiline with one value per line and the + first line (the one containing the field name) empty. Each subsequent line + corresponds to one of the releases the package belongs to and looks like + this: `o=Debian,a=unstable,n=sid,l=Debian,c=main`. That is, each release line + is a comma-separated list of "key=value" pairs, each of which denotes a + Release file entry (Origin, Label, Codename, etc.) in the format of + APT_PREFERENCES(5). + +- **Source:** (optional) The name of the source package the binary + package this record is for was built from. + This field does NOT include the version of the source package unlike + the Source field in the dpkg database. The version is optionally + available in the **Source-Version:** field. + + ### Answer An answer from the external solver to APT is either a *solution* or an @@ -205,20 +276,20 @@ An answer from the external solver to APT is either a *solution* or an The following invariant on **exit codes** must hold true. When the external solver is *able to find a solution*, it will write the solution to standard output and then exit with an exit code of 0. When the -external solver is *unable to find a solution* (and s aware of that), it -will write an error to standard output and then exit with an exit code -of 0. An exit code other than 0 will be interpreted as a solver crash -with no meaningful error about dependency resolution to convey to the -user. +external solver is *unable to find a solution* (and is aware of that), +it will write an error to standard output and then exit with an exit +code of 0. An exit code other than 0 will be interpreted as a solver +crash with no meaningful error about dependency resolution to convey to +the user. #### Solution -A solution is a list of Deb 822 stanzas. Each of them could be an -install stanza (telling APT to install a specific package), a remove -stanza (telling APT to remove one), or an autoremove stanza (telling APT -about the *future* possibility of removing a package using the -Autoremove action). +A solution is a list of Deb 822 stanzas. Each of them could be an install +stanza (telling APT to install a specific new package or to upgrade or +downgrade a package to a specific version), a remove stanza (telling APT to +remove one), or an autoremove stanza (telling APT about the *future* +possibility of removing a package using the Autoremove action). An **install stanza** starts with an Install field and supports the following fields: @@ -240,6 +311,16 @@ this protocol makes no assumption on the fact that a subsequent invocation of an Autoremove action will actually remove the very same packages indicated by Autoremove stanzas in the former solution. +A package can't be installed in multiple versions at the same time, so +for each package there can at most one version be selected either for +installation or removal. This especially means that a solver is neither +allowed to represent package upgrades as a remove of the installed +version and the installation of another (the remove is implicit and must +be omitted from the solution) nor is it supported to revert previous +actions in the solution with later actions. APT is allowed to show +warnings and might even misbehave in earlier versions if a solver is +violating this assumption. + In terms of expressivity, install and remove stanzas can carry one single field each, as APT-IDs are enough to pinpoint packages to be installed/removed. Nonetheless, for protocol readability, it is