edsp: document unique package identifiers

[apt.git] / doc / external-dependency-solver-protocol.txt

diff --git a/doc/external-dependency-solver-protocol.txt b/doc/external-dependency-solver-protocol.txt
index 14e9528c8469bf588f28cef30a9b5af3592552b3..d914db30930008b1a98c92711e674c974176f687 100644 (file)
--- a/doc/external-dependency-solver-protocol.txt
+++ b/doc/external-dependency-solver-protocol.txt
@@ -58,17 +58,24 @@ configuration documentation for more, and more up to date, information.
 - **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.
 
-- **Dir::Bin::Solvers**: absolute path of the directory where to look for
-  external solvers. Defaults to `/usr/lib/apt/solvers`.
+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
@@ -171,8 +178,13 @@ 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.
+- **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
@@ -227,6 +239,12 @@ field. The following fields are supported in package stanzas:
   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
 
@@ -245,11 +263,11 @@ 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:
@@ -271,6 +289,11 @@ 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.
 
+The package identifiers of install, remove and autoremove stanzas from a single
+solution are unique. That is, a package identifier does not occur more than
+once in the solution. Every package identifier is only associated with a single
+action (either install, remove or autoremove).
+
 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