path: root/bitbake/doc/bitbake-user-manual/bitbake-user-manual-fetching.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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<chapter>
<title>File Download Support</title>

    <para>
        BitBake's fetch module is a standalone piece of library code
        that deals with the intricacies of downloading source code
        and files from remote systems.
        Fetching source code is one of the cornerstones of building software.
        As such, this module forms an important part of BitBake.
    </para>

    <para>
        The current fetch module is called "fetch2" and refers to the
        fact that it is the second major version of the API.
        The original version is obsolete and has been removed from the codebase.
        Thus, in all cases, "fetch" refers to "fetch2" in this
        manual.
    </para>

    <section id='the-download-fetch'>
        <title>The Download (Fetch)</title>

        <para>
            BitBake takes several steps when fetching source code or files.
            The fetcher codebase deals with two distinct processes in order:
            obtaining the files from somewhere (cached or otherwise)
            and then unpacking those files into a specific location and
            perhaps in a specific way.
            Getting and unpacking the files is often optionally followed
            by patching.
            Patching, however, is not covered by this module.
        </para>

        <para>
            The code to execute the first part of this process, a fetch,
            looks something like the following:
            <literallayout class='monospaced'>
     src_uri = (d.getVar('SRC_URI', True) or "").split()
     fetcher = bb.fetch2.Fetch(src_uri, d)
     fetcher.download()
            </literallayout>
            This code sets up an instance of the fetch class.
            The instance uses a space-separated list of URLs from the
            <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
            variable and then calls the <filename>download</filename>
            method to download the files.
        </para>

        <para>
            The instantiation of the fetch class is usually followed by:
            <literallayout class='monospaced'>
     rootdir = l.getVar('WORKDIR', True)
     fetcher.unpack(rootdir)
            </literallayout>
            This code unpacks the downloaded files to the
            specified by <filename>WORKDIR</filename>.
            <note>
                For convenience, the naming in these examples matches
                the variables used by OpenEmbedded.
                If you want to see the above code in action, examine
                the OpenEmbedded class file <filename>base.bbclass</filename>.
            </note>
            The <filename>SRC_URI</filename> and <filename>WORKDIR</filename>
            variables are not hardcoded into the fetcher, since those fetcher
            methods can be (and are) called with different variable names.
            In OpenEmbedded for example, the shared state (sstate) code uses
            the fetch module to fetch the sstate files.
        </para>

        <para>
            When the <filename>download()</filename> method is called,
            BitBake tries to resolve the URLs by looking for source files
            in a specific search order:
            <itemizedlist>
                <listitem><para><emphasis>Pre-mirror Sites:</emphasis>
                    BitBake first uses pre-mirrors to try and find source files.
                    These locations are defined using the
                    <link linkend='var-PREMIRRORS'><filename>PREMIRRORS</filename></link>
                    variable.
                    </para></listitem>
                <listitem><para><emphasis>Source URI:</emphasis>
                    If pre-mirrors fail, BitBake uses the original URL (e.g from
                    <filename>SRC_URI</filename>).
                    </para></listitem>
                <listitem><para><emphasis>Mirror Sites:</emphasis>
                    If fetch failures occur, BitBake next uses mirror locations as
                    defined by the
                    <link linkend='var-MIRRORS'><filename>MIRRORS</filename></link>
                    variable.
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            For each URL passed to the fetcher, the fetcher
            calls the submodule that handles that particular URL type.
            This behavior can be the source of some confusion when you
            are providing URLs for the <filename>SRC_URI</filename>
            variable.
            Consider the following two URLs:
            <literallayout class='monospaced'>
     http://git.yoctoproject.org/git/poky;protocol=git
     git://git.yoctoproject.org/git/poky;protocol=http
            </literallayout>
            In the former case, the URL is passed to the
            <filename>wget</filename> fetcher, which does not
            understand "git".
            Therefore, the latter case is the correct form since the
            Git fetcher does know how to use HTTP as a transport.
        </para>

        <para>
            Here are some examples that show commonly used mirror
            definitions:
            <literallayout class='monospaced'>
     PREMIRRORS ?= "\
         bzr://.*/.*   http://somemirror.org/sources/ \n \
         cvs://.*/.*   http://somemirror.org/sources/ \n \
         git://.*/.*   http://somemirror.org/sources/ \n \
         hg://.*/.*    http://somemirror.org/sources/ \n \
         osc://.*/.*   http://somemirror.org/sources/ \n \
         p4://.*/.*    http://somemirror.org/sources/ \n \
         svn://.*/.*   http://somemirror.org/sources/ \n"

     MIRRORS =+ "\
         ftp://.*/.*      http://somemirror.org/sources/ \n \
         http://.*/.*     http://somemirror.org/sources/ \n \
         https://.*/.*    http://somemirror.org/sources/ \n"
            </literallayout>
            It is useful to note that BitBake supports
            cross-URLs.
            It is possible to mirror a Git repository on an HTTP
            server as a tarball.
            This is what the <filename>git://</filename> mapping in
            the previous example does.
        </para>

        <para>
            Since network accesses are slow, Bitbake maintains a
            cache of files downloaded from the network.
            Any source files that are not local (i.e.
            downloaded from the Internet) are placed into the download
            directory, which is specified by the
            <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
            variable.
        </para>

        <para>
            File integrity is of key importance for reproducing builds.
            For non-local archive downloads, the fetcher code can verify
            SHA-256 and MD5 checksums to ensure the archives have been
            downloaded correctly.
            You can specify these checksums by using the
            <filename>SRC_URI</filename> variable with the appropriate
            varflags as follows:
            <literallayout class='monospaced'>
     SRC_URI[md5sum] = "<replaceable>value</replaceable>"
     SRC_URI[sha256sum] = "<replaceable>value</replaceable>"
            </literallayout>
            You can also specify the checksums as parameters on the
            <filename>SRC_URI</filename> as shown below:
            <literallayout class='monospaced'>
     SRC_URI = "http://example.com/foobar.tar.bz2;md5sum=4a8e0f237e961fd7785d19d07fdb994d"
            </literallayout>
            If multiple URIs exist, you can specify the checksums either
            directly as in the previous example, or you can name the URLs.
            The following syntax shows how you name the URIs:
            <literallayout class='monospaced'>
     SRC_URI = "http://example.com/foobar.tar.bz2;name=foo"
     SRC_URI[foo.md5sum] = 4a8e0f237e961fd7785d19d07fdb994d
            </literallayout>
            After a file has been downloaded and has had its checksum checked,
            a ".done" stamp is placed in <filename>DL_DIR</filename>.
            BitBake uses this stamp during subsequent builds to avoid
            downloading or comparing a checksum for the file again.
            <note>
                It is assumed that local storage is safe from data corruption.
                If this were not the case, there would be bigger issues to worry about.
            </note>
        </para>

        <para>
            If
            <link linkend='var-BB_STRICT_CHECKSUM'><filename>BB_STRICT_CHECKSUM</filename></link>
            is set, any download without a checksum triggers an
            error message.
            The
            <link linkend='var-BB_NO_NETWORK'><filename>BB_NO_NETWORK</filename></link>
            variable can be used to make any attempted network access a fatal
            error, which is useful for checking that mirrors are complete
            as well as other things.
        </para>
    </section>

    <section id='bb-the-unpack'>
        <title>The Unpack</title>

        <para>
            The unpack process usually immediately follows the download.
            For all URLs except Git URLs, BitBake uses the common
            <filename>unpack</filename> method.
        </para>

        <para>
            A number of parameters exist that you can specify within the
            URL to govern the behavior of the unpack stage:
            <itemizedlist>
                <listitem><para><emphasis>unpack:</emphasis>
                    Controls whether the URL components are unpacked.
                    If set to "1", which is the default, the components
                    are unpacked.
                    If set to "0", the unpack stage leaves the file alone.
                    This parameter is useful when you want an archive to be
                    copied in and not be unpacked.
                    </para></listitem>
                <listitem><para><emphasis>dos:</emphasis>
                    Applies to <filename>.zip</filename> and
                    <filename>.jar</filename> files and specifies whether to
                    use DOS line ending conversion on text files.
                    </para></listitem>
                <listitem><para><emphasis>basepath:</emphasis>
                    Instructs the unpack stage to strip the specified
                    directories from the source path when unpacking.
                    </para></listitem>
                <listitem><para><emphasis>subdir:</emphasis>
                    Unpacks the specific URL to the specified subdirectory
                    within the root directory.
                    </para></listitem>
            </itemizedlist>
            The unpack call automatically decompresses and extracts files
            with ".Z", ".z", ".gz", ".xz", ".zip", ".jar", ".ipk", ".rpm".
            ".srpm", ".deb" and ".bz2" extensions as well as various combinations
            of tarball extensions.
        </para>

        <para>
            As mentioned, the Git fetcher has its own unpack method that
            is optimized to work with Git trees.
            Basically, this method works by cloning the tree into the final
            directory.
            The process is completed using references so that there is
            only one central copy of the Git metadata needed.
        </para>
    </section>

    <section id='bb-fetchers'>
        <title>Fetchers</title>

        <para>
            As mentioned earlier, the URL prefix determines which
            fetcher submodule BitBake uses.
            Each submodule can support different URL parameters,
            which are described in the following sections.
        </para>

        <section id='local-file-fetcher'>
            <title>Local file fetcher (<filename>file://</filename>)</title>

            <para>
                This submodule handles URLs that begin with
                <filename>file://</filename>.
                The filename you specify within the URL can be
                either an absolute or relative path to a file.
                If the filename is relative, the contents of the
                <link linkend='var-FILESPATH'><filename>FILESPATH</filename></link>
                variable is used in the same way
                <filename>PATH</filename> is used to find executables.
                Failing that,
                <link linkend='var-FILESDIR'><filename>FILESDIR</filename></link>
                is used to find the appropriate relative file.
                <note>
                    <filename>FILESDIR</filename> is deprecated and can
                    be replaced with <filename>FILESPATH</filename>.
                    Because <filename>FILESDIR</filename> is likely to be
                    removed, you should not use this variable in any new code.
                </note>
                If the file cannot be found, it is assumed that it is available in
                <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
                by the time the <filename>download()</filename> method is called.
            </para>

            <para>
                If you specify a directory, the entire directory is
                unpacked.
            </para>

            <para>
                Here are a couple of example URLs, the first relative and
                the second absolute:
                <literallayout class='monospaced'>
     SRC_URI = "file://relativefile.patch"
     SRC_URI = "file:///Users/ich/very_important_software"
                </literallayout>
            </para>
        </section>

        <section id='http-ftp-fetcher'>
            <title>HTTP/FTP wget fetcher (<filename>http://</filename>, <filename>ftp://</filename>, <filename>https://</filename>)</title>

            <para>
                This fetcher obtains files from web and FTP servers.
                Internally, the fetcher uses the wget utility.
            </para>

            <para>
                The executable and parameters used are specified by the
                <filename>FETCHCMD_wget</filename> variable, which defaults
                to sensible values.
                The fetcher supports a parameter "downloadfilename" that
                allows the name of the downloaded file to be specified.
                Specifying the name of the downloaded file is useful
                for avoiding collisions in
                <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
                when dealing with multiple files that have the same name.
            </para>

            <para>
                Some example URLs are as follows:
                <literallayout class='monospaced'>
     SRC_URI = "http://oe.handhelds.org/not_there.aac"
     SRC_URI = "ftp://oe.handhelds.org/not_there_as_well.aac"
     SRC_URI = "ftp://you@oe.handhelds.org/home/you/secret.plan"
                </literallayout>
            </para>
            <note>
               Because URL parameters are delimited by semi-colons, this can
               introduce ambiguity when parsing URLs that also contain semi-colons,
               for example:
                <literallayout class='monospaced'>
     SRC_URI = "http://abc123.org/git/?p=gcc/gcc.git;a=snapshot;h=a5dd47"
                </literallayout>
               Such URLs should should be modified by replacing semi-colons with '&amp;' characters:
               <literallayout class='monospaced'>
     SRC_URI = "http://abc123.org/git/?p=gcc/gcc.git&amp;a=snapshot&amp;h=a5dd47"
                </literallayout>
                In most cases this should work. Treating semi-colons and '&amp;' in queries
                identically is recommended by the World Wide Web Consortium (W3C).
                Note that due to the nature of the URL, you may have to specify the name
                of the downloaded file as well:
              <literallayout class='monospaced'>
     SRC_URI = "http://abc123.org/git/?p=gcc/gcc.git&amp;a=snapshot&amp;h=a5dd47;downloadfilename=myfile.bz2"
                </literallayout>
            </note>
        </section>

        <section id='cvs-fetcher'>
            <title>CVS fetcher (<filename>(cvs://</filename>)</title>

            <para>
                This submodule handles checking out files from the
                CVS version control system.
                You can configure it using a number of different variables:
                <itemizedlist>
                    <listitem><para><emphasis><filename>FETCHCMD_cvs</filename>:</emphasis>
                        The name of the executable to use when running
                        the <filename>cvs</filename> command.
                        This name is usually "cvs".
                        </para></listitem>
                    <listitem><para><emphasis><filename>SRCDATE</filename>:</emphasis>
                        The date to use when fetching the CVS source code.
                        A special value of "now" causes the checkout to
                        be updated on every build.
                        </para></listitem>
                    <listitem><para><emphasis><link linkend='var-CVSDIR'><filename>CVSDIR</filename></link>:</emphasis>
                        Specifies where a temporary checkout is saved.
                        The location is often <filename>DL_DIR/cvs</filename>.
                        </para></listitem>
                    <listitem><para><emphasis><filename>CVS_PROXY_HOST</filename>:</emphasis>
                        The name to use as a "proxy=" parameter to the
                        <filename>cvs</filename> command.
                        </para></listitem>
                    <listitem><para><emphasis><filename>CVS_PROXY_PORT</filename>:</emphasis>
                        The port number to use as a "proxyport=" parameter to
                        the <filename>cvs</filename> command.
                        </para></listitem>
                </itemizedlist>
                As well as the standard username and password URL syntax,
                you can also configure the fetcher with various URL parameters:
            </para>

            <para>
                The supported parameters are as follows:
                <itemizedlist>
                    <listitem><para><emphasis>"method":</emphasis>
                        The protocol over which to communicate with the CVS server.
                        By default, this protocol is "pserver".
                        If "method" is set to "ext", BitBake examines the
                        "rsh" parameter and sets <filename>CVS_RSH</filename>.
                        You can use "dir" for local directories.
                        </para></listitem>
                    <listitem><para><emphasis>"module":</emphasis>
                        Specifies the module to check out.
                        You must supply this parameter.
                        </para></listitem>
                    <listitem><para><emphasis>"tag":</emphasis>
                        Describes which CVS TAG should be used for
                        the checkout.
                        By default, the TAG is empty.
                        </para></listitem>
                    <listitem><para><emphasis>"date":</emphasis>
                        Specifies a date.
                        If no "date" is specified, the
                        <link linkend='var-SRCDATE'><filename>SRCDATE</filename></link>
                        of the configuration is used to checkout a specific date.
                        The special value of "now" causes the checkout to be
                        updated on every build.
                        </para></listitem>
                    <listitem><para><emphasis>"localdir":</emphasis>
                        Used to rename the module.
                        Effectively, you are renaming the output directory
                        to which the module is unpacked.
                        You are forcing the module into a special
                        directory relative to
                        <link linkend='var-CVSDIR'><filename>CVSDIR</filename></link>.
                        </para></listitem>
                    <listitem><para><emphasis>"rsh"</emphasis>
                        Used in conjunction with the "method" parameter.
                        </para></listitem>
                    <listitem><para><emphasis>"scmdata":</emphasis>
                        Causes the CVS metadata to be maintained in the tarball
                        the fetcher creates when set to "keep".
                        The tarball is expanded into the work directory.
                        By default, the CVS metadata is removed.
                        </para></listitem>
                    <listitem><para><emphasis>"fullpath":</emphasis>
                        Controls whether the resulting checkout is at the
                        module level, which is the default, or is at deeper
                        paths.
                        </para></listitem>
                    <listitem><para><emphasis>"norecurse":</emphasis>
                        Causes the fetcher to only checkout the specified
                        directory with no recurse into any subdirectories.
                        </para></listitem>
                    <listitem><para><emphasis>"port":</emphasis>
                        The port to which the CVS server connects.
                        </para></listitem>
                </itemizedlist>
                Some example URLs are as follows:
                <literallayout class='monospaced'>
     SRC_URI = "cvs://CVSROOT;module=mymodule;tag=some-version;method=ext"
     SRC_URI = "cvs://CVSROOT;module=mymodule;date=20060126;localdir=usethat"
                </literallayout>
            </para>
        </section>

        <section id='svn-fetcher'>
            <title>Subversion (SVN) Fetcher (<filename>svn://</filename>)</title>

            <para>
                This fetcher submodule fetches code from the
                Subversion source control system.
                The executable used is specified by
                <filename>FETCHCMD_svn</filename>, which defaults
                to "svn".
                The fetcher's temporary working directory is set by
                <link linkend='var-SVNDIR'><filename>SVNDIR</filename></link>,
                which is usually <filename>DL_DIR/svn</filename>.
            </para>

            <para>
                The supported parameters are as follows:
                <itemizedlist>
                    <listitem><para><emphasis>"module":</emphasis>
                        The name of the svn module to checkout.
                        You must provide this parameter.
                        You can think of this parameter as the top-level
                        directory of the repository data you want.
                        </para></listitem>
                    <listitem><para><emphasis>"protocol":</emphasis>
                        The protocol to use, which defaults to "svn".
                        Other options are "svn+ssh" and "rsh".
                        For "rsh", the "rsh" parameter is also used.
                        </para></listitem>
                    <listitem><para><emphasis>"rev":</emphasis>
                        The revision of the source code to checkout.
                        </para></listitem>
                    <listitem><para><emphasis>"date":</emphasis>
                        The date of the source code to checkout.
                        Specific revisions are generally much safer to checkout
                        rather than by date as they do not involve timezones
                        (e.g. they are much more deterministic).
                        </para></listitem>
                    <listitem><para><emphasis>"scmdata":</emphasis>
                        Causes the “.svn” directories to be available during
                        compile-time when set to "keep".
                        By default, these directories are removed.
                        </para></listitem>
                    <listitem><para><emphasis>"transportuser":</emphasis>
                        When required, sets the username for the transport.
                        By default, this parameter is empty.
                        The transport username is different than the username
                        used in the main URL, which is passed to the subversion
                        command.
                        </para></listitem>
                </itemizedlist>
                Following are two examples using svn:
                <literallayout class='monospaced'>
     SRC_URI = "svn://svn.oe.handhelds.org/svn;module=vip;proto=http;rev=667"
     SRC_URI = "svn://svn.oe.handhelds.org/svn/;module=opie;proto=svn+ssh;date=20060126"
                </literallayout>
            </para>
        </section>

        <section id='git-fetcher'>
            <title>Git Fetcher (<filename>git://</filename>)</title>

            <para>
                This fetcher submodule fetches code from the Git
                source control system.
                The fetcher works by creating a bare clone of the
                remote into
                <link linkend='var-GITDIR'><filename>GITDIR</filename></link>,
                which is usually <filename>DL_DIR/git2</filename>.
                This bare clone is then cloned into the work directory during the
                unpack stage when a specific tree is checked out.
                This is done using alternates and by reference to
                minimize the amount of duplicate data on the disk and
                make the unpack process fast.
                The executable used can be set with
                <filename>FETCHCMD_git</filename>.
            </para>

            <para>
                This fetcher supports the following parameters:
                <itemizedlist>
                    <listitem><para><emphasis>"protocol":</emphasis>
                        The protocol used to fetch the files.
                        The default is "git" when a hostname is set.
                        If a hostname is not set, the Git protocol is "file".
                        You can also use "http", "https", "ssh" and "rsync".
                        </para></listitem>
                    <listitem><para><emphasis>"nocheckout":</emphasis>
                        Tells the fetcher to not checkout source code when
                        unpacking when set to "1".
                        Set this option for the URL where there is a custom
                        routine to checkout code.
                        The default is "0".
                        </para></listitem>
                    <listitem><para><emphasis>"rebaseable":</emphasis>
                        Indicates that the upstream Git repository can be rebased.
                        You should set this parameter to "1" if
                        revisions can become detached from branches.
                        In this case, the source mirror tarball is done per
                        revision, which has a loss of efficiency.
                        Rebasing the upstream Git repository could cause the
                        current revision to disappear from the upstream repository.
                        This option reminds the fetcher to preserve the local cache
                        carefully for future use.
                        The default value for this parameter is "0".
                        </para></listitem>
                    <listitem><para><emphasis>"nobranch":</emphasis>
                        Tells the fetcher to not check the SHA validation
                        for the branch when set to "1".
                        The default is "0".
                        Set this option for the recipe that refers to
                        the commit that is valid for a tag instead of
                        the branch.
                        </para></listitem>
                    <listitem><para><emphasis>"bareclone":</emphasis>
                        Tells the fetcher to clone a bare clone into the
                        destination directory without checking out a working tree.
                        Only the raw Git metadata is provided.
                        This parameter implies the "nocheckout" parameter as well.
                        </para></listitem>
                    <listitem><para><emphasis>"branch":</emphasis>
                        The branch(es) of the Git tree to clone.
                        If unset, this is assumed to be "master".
                        The number of branch parameters much match the number of
                        name parameters.
                        </para></listitem>
                    <listitem><para><emphasis>"rev":</emphasis>
                        The revision to use for the checkout.
                        The default is "master".
                        </para></listitem>
                    <listitem><para><emphasis>"tag":</emphasis>
                        Specifies a tag to use for the checkout.
                        To correctly resolve tags, BitBake must access the
                        network.
                        For that reason, tags are often not used.
                        As far as Git is concerned, the "tag" parameter behaves
                        effectively the same as the "rev" parameter.
                        </para></listitem>
                    <listitem><para><emphasis>"subpath":</emphasis>
                        Limits the checkout to a specific subpath of the tree.
                        By default, the whole tree is checked out.
                        </para></listitem>
                    <listitem><para><emphasis>"destsuffix":</emphasis>
                        The name of the path in which to place the checkout.
                        By default, the path is <filename>git/</filename>.
                        </para></listitem>
                </itemizedlist>
                Here are some example URLs:
                <literallayout class='monospaced'>
     SRC_URI = "git://git.oe.handhelds.org/git/vip.git;tag=version-1"
     SRC_URI = "git://git.oe.handhelds.org/git/vip.git;protocol=http"
                </literallayout>
            </para>
        </section>

        <section id='gitsm-fetcher'>
            <title>Git Submodule Fetcher (<filename>gitsm://</filename>)</title>

            <para>
                This fetcher submodule inherits from the
                <link linkend='git-fetcher'>Git fetcher</link> and extends
                that fetcher's behavior by fetching a repository's submodules.
                <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
                is passed to the Git fetcher as described in the
                "<link linkend='git-fetcher'>Git Fetcher (<filename>git://</filename>)</link>"
                section.
                <note>
                    <title>Notes and Warnings</title>
                    <para>
                        You must clean a recipe when switching between
                        '<filename>git://</filename>' and
                        '<filename>gitsm://</filename>' URLs.
                    </para>

                    <para>
                        The Git Submodules fetcher is not a complete fetcher
                        implementation.
                        The fetcher has known issues where it does not use the
                        normal source mirroring infrastructure properly.
                    </para>
                </note>
            </para>
        </section>

        <section id='clearcase-fetcher'>
            <title>ClearCase Fetcher (<filename>ccrc://</filename>)</title>

            <para>
                This fetcher submodule fetches code from a
                <ulink url='http://en.wikipedia.org/wiki/Rational_ClearCase'>ClearCase</ulink>
                repository.
            </para>

            <para>
                To use this fetcher, make sure your recipe has proper
                <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>,
                <link linkend='var-SRCREV'><filename>SRCREV</filename></link>, and
                <link linkend='var-PV'><filename>PV</filename></link> settings.
                Here is an example:
                <literallayout class='monospaced'>
     SRC_URI = "ccrc://cc.example.org/ccrc;vob=/example_vob;module=/example_module"
     SRCREV = "EXAMPLE_CLEARCASE_TAG"
     PV = "${@d.getVar("SRCREV", False).replace("/", "+")}"
                </literallayout>
                The fetcher uses the <filename>rcleartool</filename> or
                <filename>cleartool</filename> remote client, depending on
                which one is available.
            </para>

            <para>
                Following are options for the <filename>SRC_URI</filename>
                statement:
                <itemizedlist>
                    <listitem><para><emphasis><filename>vob</filename></emphasis>:
                        The name, which must include the
                        prepending "/" character, of the ClearCase VOB.
                        This option is required.
                        </para></listitem>
                    <listitem><para><emphasis><filename>module</filename></emphasis>:
                        The module, which must include the
                        prepending "/" character, in the selected VOB.
                        <note>
                            The <filename>module</filename> and <filename>vob</filename>
                            options are combined to create the <filename>load</filename> rule in
                            the view config spec.
                            As an example, consider the <filename>vob</filename> and
                            <filename>module</filename> values from the
                            <filename>SRC_URI</filename> statement at the start of this section.
                            Combining those values results in the following:
                            <literallayout class='monospaced'>
     load /example_vob/example_module
                            </literallayout>
                        </note>
                        </para></listitem>
                    <listitem><para><emphasis><filename>proto</filename></emphasis>:
                        The protocol, which can be either <filename>http</filename> or
                        <filename>https</filename>.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                By default, the fetcher creates a configuration specification.
                If you want this specification written to an area other than the default,
                use the <filename>CCASE_CUSTOM_CONFIG_SPEC</filename> variable
                in your recipe to define where the specification is written.
                <note>
                    the <filename>SRCREV</filename> loses its functionality if you
                    specify this variable.
                    However, <filename>SRCREV</filename> is still used to label the
                    archive after a fetch even though it does not define what is
                    fetched.
                </note>
            </para>

            <para>
                Here are a couple of other behaviors worth mentioning:
                <itemizedlist>
                    <listitem><para>
                        When using <filename>cleartool</filename>, the login of
                        <filename>cleartool</filename> is handled by the system.
                        The login require no special steps.
                        </para></listitem>
                    <listitem><para>
                        In order to use <filename>rcleartool</filename> with authenticated
                        users, an "rcleartool login" is necessary before using the fetcher.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='perforce-fetcher'>
            <title>Perforce Fetcher (<filename>p4://</filename>)</title>

            <para>
                This fetcher submodule fetches code from the
                <ulink url='https://www.perforce.com/'>Perforce</ulink>
                source control system.
                The executable used is specified by
                <filename>FETCHCMD_p4</filename>, which defaults
                to "p4".
                The fetcher's temporary working directory is set by
                <link linkend='var-P4DIR'><filename>P4DIR</filename></link>,
                which defaults to "DL_DIR/p4".
            </para>

            <para>
                To use this fetcher, make sure your recipe has proper
                <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>,
                <link linkend='var-SRCREV'><filename>SRCREV</filename></link>, and
                <link linkend='var-PV'><filename>PV</filename></link> values.
                The p4 executable is able to use the config file defined by your
                system's <filename>P4CONFIG</filename> environment variable in
                order to define the Perforce server URL and port, username, and
                password if you do not wish to keep those values in a recipe
                itself.
                If you choose not to use <filename>P4CONFIG</filename>,
                or to explicitly set variables that <filename>P4CONFIG</filename>
                can contain, you can specify the <filename>P4PORT</filename> value,
                which is the server's URL and port number, and you can
                specify a username and password directly in your recipe within
                <filename>SRC_URI</filename>.
            </para>

            <para>
                Here is an example that relies on <filename>P4CONFIG</filename>
                to specify the server URL and port, username, and password, and
                fetches the Head Revision:
                <literallayout class='monospaced'>
    SRC_URI = "p4://example-depot/main/source/..."
    SRCREV = "${AUTOREV}"
    PV = "p4-${SRCPV}"
    S = "${WORKDIR}/p4"
                </literallayout>
            </para>

            <para>
                Here is an example that specifies the server URL and port,
                username, and password, and fetches a Revision based on a Label:
                <literallayout class='monospaced'>
    P4PORT = "tcp:p4server.example.net:1666"
    SRC_URI = "p4://user:passwd@example-depot/main/source/..."
    SRCREV = "release-1.0"
    PV = "p4-${SRCPV}"
    S = "${WORKDIR}/p4"
                </literallayout>
                <note>
                    You should always set <filename>S</filename>
                    to <filename>"${WORKDIR}/p4"</filename> in your recipe.
                </note>
            </para>
        </section>

        <section id='other-fetchers'>
            <title>Other Fetchers</title>

            <para>
                Fetch submodules also exist for the following:
                <itemizedlist>
                    <listitem><para>
                        Bazaar (<filename>bzr://</filename>)
                        </para></listitem>
                    <listitem><para>
                        Trees using Git Annex (<filename>gitannex://</filename>)
                        </para></listitem>
                    <listitem><para>
                        Secure FTP (<filename>sftp://</filename>)
                        </para></listitem>
                    <listitem><para>
                        Secure Shell (<filename>ssh://</filename>)
                        </para></listitem>
                    <listitem><para>
                        Repo (<filename>repo://</filename>)
                        </para></listitem>
                    <listitem><para>
                        OSC (<filename>osc://</filename>)
                        </para></listitem>
                    <listitem><para>
                        Mercurial (<filename>hg://</filename>)
                        </para></listitem>
                </itemizedlist>
                No documentation currently exists for these lesser used
                fetcher submodules.
                However, you might find the code helpful and readable.
            </para>
        </section>
    </section>

    <section id='auto-revisions'>
        <title>Auto Revisions</title>

        <para>
            We need to document <filename>AUTOREV</filename> and
            <filename>SRCREV_FORMAT</filename> here.
        </para>
    </section>
</chapter>