acquire: Use priority queues and a 3 stage pipeline design

[apt.git] / doc / acquire-additional-files.txt

diff --git a/doc/acquire-additional-files.txt b/doc/acquire-additional-files.txt
index 32b0e4470b144c837bf865eac165d5138bb9697f..c9bea068f4724669174e0140ea4a53d3950aa7a4 100644 (file)
--- a/doc/acquire-additional-files.txt
+++ b/doc/acquire-additional-files.txt
@@ -46,10 +46,11 @@ multiple types!
 
 After the type you can pick any valid and unique string which preferable
 refers to the file it downloads (In the example we picked 'Packages').
-This string is used as identifier for the target class and accessible as
-'Created-By' e.g. in the "apt-get indextargets" output as detailed
-below.  It is also used to allow user to enable/disable targets per
-sources.list entry.
+This string is used as identifier (if not explicitly set otherwise) for
+the target class and accessible as 'Identifier' and 'Created-By' e.g.
+in the "apt-get indextargets" output as detailed below. The identifier
+is also used to allow user to enable/disable targets per sources.list
+entry.
 
 All targets have three main properties you can define:
 * MetaKey: The identifier of the file to be downloaded as used in the
@@ -71,6 +72,12 @@ All targets have three main properties you can define:
 
 
 Additional optional properties:
+* Identifier: The default value is the unique string identifying this
+  file (in the example above it was 'Packages') also accessible as
+  Created-By. The difference is that using this property multiple files
+  can be subsumed under one identifier e.g. if you configure multiple
+  possible locations for the files (with Fallback-Of), but the front-end
+  doesn't need to handle files from the different locations differently.
 * DefaultEnabled: The default value is 'yes' which means that apt will
   try to acquire this target from all sources. If set to 'no' the user
   has to explicitly enable this target in the sources.list file with the
@@ -90,6 +97,11 @@ Additional optional properties:
   have to ensure your front-end can deal with all compressed fileformats
   supported by apt (libapt users can e.g. use FileFd, others can use
   the cat-file command of /usr/lib/apt/apt-helper).
+* Fallback-Of: Is by default not set. If it is set and specifies another
+  target name (see Created-By) which was found in the Release file the
+  download of this target will be skipped. This can be used to implement
+  fallback(chain)s to allow transitions like the rename of target files.
+  The behavior if cycles are formed with Fallback-Of is undefined!
 * flat{MetaKey,Description}: APT supports two types of repositories:
   dists-style repositories which are the default and by far the most
   common which are named after the fact that the files are in an
@@ -124,6 +136,10 @@ aren't accidentally used by front-ends:
   type a front-end can't open transparently. This should always be
   a temporary workaround through and a bug should be reported against
   the front-end in question.
+* KeepCompressedAs: The default value is a space separated list of
+  compression types supported by apt (see previous option) which is
+  sorted by the cost-value of the compression in ascending order,
+  except that cost=0 "compressions" (like uncompressed) are listed last.
 
 
 # More examples
@@ -198,13 +214,13 @@ own output style. The variables are what you see in the output, just all
 uppercase and wrapped in $(), as in the configuration file.
 
 To get all the filenames of all Translation-en files you can e.g. call:
-       apt-get indextargets --format '$(FILENAME)' "Created-By: Translations" "Language: en"
+       apt-get indextargets --format '$(FILENAME)' "Identifier: Translations" "Language: en"
 
-The line-based filtering and the formating is rather crude and feature-
+The line-based filtering and the formatting is rather crude and feature-
 less by design: The default format is Debians standard format deb822 (in
 particular: Field names are case-insensitive and the order of fields in
 the stanza is undefined), so instead of apt reimplementing powerful
-filters and formating for this command, it is recommend to use piping
+filters and formatting for this command, it is recommend to use piping
 and dedicated tools like 'grep-dctrl' if you need more than the basics
 provided.
 
@@ -237,6 +253,9 @@ Remarks on fields only available in (default) --release-info mode:
 Remarks on other available fields:
 * MetaKey, ShortDesc, Description, Site, Release: as defined
   by the configuration and described further above.
+* Identifier: Defaults to the value of Created-By, but can be set
+  explicitly in the configuration (see above). Prefer this field over
+  Created-By to subsume multiple file(location)s (see Fallback-Of).
 * Created-By: configuration entity responsible for this target
 * Target-Of: type of the sources.list entry
 * URI, Repo-URI: avoid using. Contains potentially username/password.