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authorJohannes 'josch' Schauer <josch@mister-muffin.de>2016-05-12 13:07:59 +0200
committerDavid Kalnischkies <david@kalnischkies.de>2016-05-12 14:52:29 +0200
commitd67db03c2ab853eba7b67c8870af41796eea387c (patch)
treeb1d49d1db6a6675fca3bf5211d3464843b6e2970 /doc
parent5b0577488ff60e7163fe7dc62a044329d398d726 (diff)
edsp: document unique package identifiers
Document that package identifiers must be unique (apt only uses the last action for a given identifier) and that install requests do also imply upgrades and downgrades (and thus removal of the old version). This is to prevent that solvers express an upgrade or downgrade instruction as two stanzas: a removal of the old version and an installation of the new version. Instead, a single install stanza is sufficient to express upgrade or downgrade requests.
Diffstat (limited to 'doc')
-rw-r--r--doc/external-dependency-solver-protocol.txt15
1 files changed, 10 insertions, 5 deletions
diff --git a/doc/external-dependency-solver-protocol.txt b/doc/external-dependency-solver-protocol.txt
index e2bd95866..d914db309 100644
--- a/doc/external-dependency-solver-protocol.txt
+++ b/doc/external-dependency-solver-protocol.txt
@@ -263,11 +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:
@@ -289,6 +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