apt-private: #ifdef HAVE_STRUCT_STATFS_F_TYPE, not #if

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

diff --git a/doc/acquire-additional-files.txt b/doc/acquire-additional-files.txt
index c52955619164dea7f7d6beda0f056cb62d39abeb..c9bea068f4724669174e0140ea4a53d3950aa7a4 100644 (file)
--- a/doc/acquire-additional-files.txt
+++ b/doc/acquire-additional-files.txt
@@ -4,18 +4,18 @@ The download and verification of data from multiple sources in different
 compression formats, with partial downloads and patches is an involved
 process which is hard to implement correctly and securely.
 
 compression formats, with partial downloads and patches is an involved
 process which is hard to implement correctly and securely.
 

-APT frontends share the code and binaries to make this happen in libapt
+APT front-ends share the code and binaries to make this happen in libapt

 with the Acquire system, supported by helpers shipped in the apt package
 itself and additional transports in individual packages like
 apt-transport-https.
 
 For its own operation libapt needs or can make use of Packages, Sources
 and Translation-* files, which it will acquire by default, but
 with the Acquire system, supported by helpers shipped in the apt package
 itself and additional transports in individual packages like
 apt-transport-https.
 
 For its own operation libapt needs or can make use of Packages, Sources
 and Translation-* files, which it will acquire by default, but

-a repository might contain more data files (e.g.  Contents) a frontend
+a repository might contain more data files (e.g.  Contents) a front-end

 (e.g. apt-file) might want to use and would therefore need to be
 downloaded as well.
 
 (e.g. apt-file) might want to use and would therefore need to be
 downloaded as well.
 

-This file describes the configuration scheme such a frontend can use to
+This file describes the configuration scheme such a front-end can use to

 instruct the Acquire system to download those additional files.
 
 # The Configuration Stanza
 instruct the Acquire system to download those additional files.
 
 # The Configuration Stanza


@@ -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').
 
 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
 
 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:
 
 
 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
 * 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


@@ -83,12 +90,18 @@ Additional optional properties:
   regardless of this setting.
 * KeepCompressed: The default is the value of Acquire::GzipIndexes,
   which defaults to false. If true, the acquire system will keep the
   regardless of this setting.
 * KeepCompressed: The default is the value of Acquire::GzipIndexes,
   which defaults to false. If true, the acquire system will keep the

-  file compressed on disk rather than extract it. If your frontend can't
+  file compressed on disk rather than extract it. If your front-end can't

   deal with compressed files transparently you have to explicitly set
   this option to false to avoid problems with users setting the option
   globally. On the other hand, if you set it to true or don't set it you
   deal with compressed files transparently you have to explicitly set
   this option to false to avoid problems with users setting the option
   globally. On the other hand, if you set it to true or don't set it you

-  have to ensure your frontend can deal with all compressed fileformats
-  supported by apt (libapt users can e.g. use FileFd).
+  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
 * 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


@@ -106,20 +119,27 @@ information about the compressed files/PDiffs to make this happen.
 *NO* properties have to be set to enable this!
 
 
 *NO* properties have to be set to enable this!
 
 

-More properties exist, but these should *NOT* be set by frontends
+More properties exist, but these should *NOT* be set by front-ends

 requesting files. They exist for internal and end-user usage only.
 Some of these are – which are documented here only to ensure that they
 requesting files. They exist for internal and end-user usage only.
 Some of these are – which are documented here only to ensure that they

-aren't accidentally used by frontends:
+aren't accidentally used by front-ends:

 * PDiffs: controls if apt will try to use PDiffs for this target.
   Defaults to the value of Acquire::PDiffs which is true by default.
   Can be overridden per-source by the sources.list option of the same
   name. See the documentation for both of these for details.
 * PDiffs: controls if apt will try to use PDiffs for this target.
   Defaults to the value of Acquire::PDiffs which is true by default.
   Can be overridden per-source by the sources.list option of the same
   name. See the documentation for both of these for details.

+* By-Hash: controls if apt will try to use an URI constructed from
+  a hashsum of the file to download. See the documentation for config
+  option Acquire::By-Hash and sources.list option By-Hash for details.

 * CompressionTypes: The default value is a space separated list of
   compression types supported by apt (see Acquire::CompressionTypes).
   You can set this option to prevent apt from downloading a compression
 * CompressionTypes: The default value is a space separated list of
   compression types supported by apt (see Acquire::CompressionTypes).
   You can set this option to prevent apt from downloading a compression

-  type a frontend can't open transparently. This should always be
+  type a front-end can't open transparently. This should always be

   a temporary workaround through and a bug should be reported against
   a temporary workaround through and a bug should be reported against

-  the frontend in question.
+  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
 
 
 # More examples


@@ -194,13 +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:
 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
 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.
 
 and dedicated tools like 'grep-dctrl' if you need more than the basics
 provided.
 


@@ -233,6 +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.
 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.
 * 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.


@@ -254,7 +277,7 @@ about which files they require. It is usually best to have a common
 package ship the configuration needed to get the files, but specific
 needs might require specific solutions. Again: talk to us.
 
 package ship the configuration needed to get the files, but specific
 needs might require specific solutions. Again: talk to us.
 

-Bad things will happen if multiple frontends request the same file(s)
+Bad things will happen if multiple front-ends request the same file(s)

 via different targets, which is another reason why coordination is very
 important!
 
 via different targets, which is another reason why coordination is very
 important!
 


@@ -275,7 +298,7 @@ In other words: We would be opening Pandora's box.
 
 # Acquiring files to a specific location on disk
 
 
 # Acquiring files to a specific location on disk
 

-You can't by design to avoid multiple frontends requesting the same file
+You can't by design to avoid multiple front-ends requesting the same file

 to be downloaded to multiple different places on (different) disks
 (among other reasons).  See the next point for a solution if you really
 have to force a specific location by creating symlinks.
 to be downloaded to multiple different places on (different) disks
 (among other reasons).  See the next point for a solution if you really
 have to force a specific location by creating symlinks.