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>The <SPAN
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>eCos</SPAN
> Component Writer's Guide</TH
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>Chapter 2. Package Organization</TD
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><DIV
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><H1
CLASS="SECT1"
><A
NAME="PACKAGE.VERSIONS">Package Versioning</H1
><P
>Below each package directory there can be one or more version
sub-directories, named after the versions. This is a requirement of
the component framework: it must be possible for users to install
multiple versions of a package and select which one to use for any
given application. This has a number of advantages to users: most
importantly it allows a single component repository to be shared
between multiple users and multiple projects, as required; also it
facilitates experiments, for example it is relatively easy to try out
the latest version of some package and see if it makes any difference.
There is a potential disadvantage in terms of disk space. However
since <SPAN
CLASS="APPLICATION"
>eCos</SPAN
> packages generally consist of source code intended for
small embedded systems, and given typical modern disk sizes, keeping a
number of different versions of a package installed will usually be
acceptable. The administration tool can be used to remove versions
that are no longer required.</P
><DIV
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><P
><IMG
SRC="version.png"
ALIGN="CENTER"></P
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><P
></P
></DIV
><P
>The version <TT
CLASS="FILENAME"
>current</TT
> is special. Typically it
corresponds to the very latest version of the sources, obtained by
anonymous <SPAN
CLASS="APPLICATION"
>CVS</SPAN
>. These sources may change frequently, unlike full
releases which do not change (or only when patches are produced).
Component writers may also want to work on the
<TT
CLASS="FILENAME"
>current</TT
> version.</P
><P
>All other subdirectories of a package correspond to specific releases
of that package. The component framework allows users to select the
particular version of a package they want to use, but by default the
most recent one will be used. This requires some rules for ordering
version numbers, a difficult task because of the wide variety of ways
in which versions can be identified.</P
><P
></P
><OL
TYPE="1"
><LI
><P
>The version <TT
CLASS="FILENAME"
>current</TT
> is always considered to be
the most recent version.</P
></LI
><LI
><P
>If the first character of both strings are either <TT
CLASS="LITERAL"
>v</TT
>
or <TT
CLASS="LITERAL"
>V</TT
>, these are skipped because it makes little
sense to enforce case sensitivity here. Potentially this could result
in ambiguity if there are two version directories
<TT
CLASS="LITERAL"
>V1.0</TT
> and <TT
CLASS="LITERAL"
>v1.0</TT
>, but this will
match the confusion experienced by any users of such a package.
However if two subsequent releases are called <TT
CLASS="LITERAL"
>V1.0</TT
>
and <TT
CLASS="LITERAL"
>v1.1</TT
>, e.g. because of a minor mix-up when
making the distribution file, then the case difference is ignored.</P
></LI
><LI
><P
>Next the two version strings are compared one character at a time.
If both strings are currently at a digit then a string to number
conversion takes place, and the resulting numbers are compared.
For example <TT
CLASS="LITERAL"
>v10</TT
> is a more recent release than
<TT
CLASS="LITERAL"
>v2</TT
>. If the two numbers are the same then processing
continues, so for <TT
CLASS="LITERAL"
>v2b</TT
> and <TT
CLASS="LITERAL"
>v2c</TT
>
the version comparison code would move on to <TT
CLASS="LITERAL"
>b</TT
> and
<TT
CLASS="LITERAL"
>c</TT
>. </P
></LI
><LI
><P
>The characters dot <TT
CLASS="LITERAL"
>.</TT
>, hyphen <TT
CLASS="LITERAL"
>-</TT
>
and underscore <TT
CLASS="LITERAL"
>_</TT
> are treated as equivalent
separators, so if one release goes out as <TT
CLASS="LITERAL"
>v1_1</TT
> and
the next goes out as <TT
CLASS="LITERAL"
>v1.2</TT
> the separator has no
effect.</P
></LI
><LI
><P
>If neither string has yet terminated but the characters are different,
ASCII comparison is used. For example <TT
CLASS="LITERAL"
>V1.1b</TT
> is
more recent than <TT
CLASS="LITERAL"
>v1.1alpha</TT
>.</P
></LI
><LI
><P
>If one version string terminates before the other, the current
character determines which is the more recent. If the other string is
currently at a separator character, for example
<TT
CLASS="LITERAL"
>v1.3.1</TT
> and <TT
CLASS="LITERAL"
>v1.3</TT
>, then the former
is assumed to be a minor release and hence more recent than the
latter. If the other string is not at a separator character, for
example <TT
CLASS="LITERAL"
>v1.3beta</TT
>, then it is treated as an
experimental version of the <TT
CLASS="LITERAL"
>v1.3</TT
> release and hence
older. </P
></LI
><LI
><P
>There is no special processing of dates, so with two versions
<TT
CLASS="LITERAL"
>ss-20000316</TT
> and <TT
CLASS="LITERAL"
>ss-20001111</TT
>
the numerical values <TT
CLASS="LITERAL"
>20001111</TT
> and
<TT
CLASS="LITERAL"
>20000316</TT
> determine the result: larger values are
more recent. It is suggested that the full year be used in such cases
rather than a shorthand like <TT
CLASS="LITERAL"
>00</TT
>, to avoid
Y2100 problems.</P
></LI
><LI
><P
>There is no limit on how many levels of versioning are used, so
there could in theory be a <TT
CLASS="LITERAL"
>v3.1.4.1.5.9.2.7</TT
> release
of a package. However this is unlikely to be of benefit to typical
users of a package.</P
></LI
></OL
><P
>The version comparison rules of the component framework may not be
suitable for every version numbering scheme in existence, but they
should cope with many common cases.</P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
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><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>There are some issues still to be resolved before it is possible to
combine the <TT
CLASS="FILENAME"
>current</TT
> sources available via
anonymous <SPAN
CLASS="APPLICATION"
>CVS</SPAN
> and full releases of <SPAN
CLASS="APPLICATION"
>eCos</SPAN
> and additional packages in
a single component repository. The first problem relates to the
<SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> database: if a new package is added via
the CVS repository then this requires a database update, but the
administration tool is bypassed. The second problem arises if an
organization chooses to place its component repository under source
code control using <SPAN
CLASS="APPLICATION"
>CVS</SPAN
>, in which case different directories will
belong to different <SPAN
CLASS="APPLICATION"
>CVS</SPAN
> servers. These issues will be addressed in a
future release.</P
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