boinc/doc/files.php

<?php
require_once("docutil.php");
page_head("Storage");
echo "
<h3>Files and data servers</h3> 
<p>
The BOINC storage model is based on <b>files</b>.
Examples of files:
<ul>
<li> The inputs and outputs of applications;
<li> Application executables, libraries, etc.
</ul>
<p>
The BOINC core client transfers files to and from project-operated
<b>data servers</b> using HTTP.
<p>
A file is described by an XML element of the form 
".html_text("
<file_info>
    <name>foobar</name>
    <url>http://a.b.c/foobar</url>
    <url>http://x.y.z/foobar</url>
    ...
    <md5_cksum>123123123123</md5_cksum>
    <nbytes>134423</nbytes>
    <max_nbytes>200000</max_nbytes>
    <status>1</status>
    [ <generated_locally/> ]
    [ <executable/> ]
    [ <upload_when_present/> ]
    [ <sticky/> ]
    [ <signature_required/> ]
    [ <no_delete/> ]
    [ <report_on_rpc/> ]
</file_info>
")."
The elements are as follows:
";
list_start();
list_item(
    "name", "The file's name, which must be unique within the project."
);
list_item("url",
    "a URL where the file is (or will be) located on a data server."
);
list_item("md5_cksum", "The MD5 checksum of the file."
);
list_item("nbytes",
    "the size of the file in bytes (may be greater than 2^32)."
);
list_item("max_nbytes",
    "The maximum allowable size of the file in bytes (may be greater than 2^32).
    This is used to prevent flooding data servers with bogus data."
);
list_item("status",
    "0 if the file is not present,
    1 if the file is present, or a negative error code if there was a
    problem in downloading or generating the file."
);
list_item("generated_locally",
    "If present, indicates that the file will be generated by an application on
    the client, as opposed to being downloaded."
);
list_item("executable",
    "If present, indicates that the file protections should be set to allow
    execution."
);
list_item("upload_when_present",
    "If present, indicates that the file should be uploaded
     when the application that generates it exits.
");
list_item("sticky",
    "If present, indicates that the file should be retained
    on the client after its initial use."
);
list_item("signature_required",
    "If present, indicates that the file should be verified with an
    RSA signature.
    This generally only applies to executable files."
);
list_item("no_delete",
    "If present for an input (workunit) file,
    indicates that the file should NOT be removed from the data server's
    download directory when the workunit is completed.
    Use this if a particular input file or files are used by more than one
    workunit, or will be used by future workunits."
);
list_item("no_delete",
    "If present for an output (result) file,
    indicates that the file should NOT be removed from the data server's upload
    directory when the corresponding workunit is completed.
    Use with caution - this may cause your upload directory to overflow."
);
list_item("report_on_rpc",
    "Include a description of this file in scheduler RPC requests,
    so that the scheduler may send appropriate work
    using <a href=sched_locality.php>locality scheduling</a>."
);
list_end();
echo "
<p>
Once a file is created (on a data server or a participant host) it
is <b>immutable</b>.
This means that all replicas of that file are assumed to be identical.

<h3>File references</h3> 
<p>
Files may be associated with <a href=work.php>workunits</a>,
<a href=result.php>results</a> and
<a href=app.php>application versions</a>.
Each such association is represented by an XML element of the form 
".html_text("
<file_ref>
    <file_name>foobar</file_name>
    [ <open_name>input</open_name> ]
    [ <main_program/> ]
</file_ref>
")."
The elements are as follows: 
";
list_start();
list_item("file_name", "Specifies a file.");
list_item("open_name", "The name by
which the application will refer to the file.");
list_item("main_program", "Used for files
associated with application versions.
It indicates that this file is the application's main program.");
list_end();

echo "
<h3>File management</h3>
<p>
BOINC's default behavior is to delete files around
when they aren't needed any more.
Specifically:
<ul>
<li> On the client, input files are deleted when no workunit refers to them,
and output files are deleted when no result refers to them.
Application-version files are deleted when they are referenced
only from superceded application versions.
<li> On the client, the 'sticky' flag overrides the above mechanisms
and suppresses the deletion of the file.
The file may deleted by an explicit
<a href=delete_file.php>server request</a>.
The file may also be deleted at any time by the core client
in order to honor limits on disk-space usage.
<li> On the server, the <a href=file_deleter.php>file deleter daemon</a>
deletes input and output files that are no longer needed.
This can be suppressed using the 'no_delete' flag,
or using command-line options to the file deleter.
</ul>
";
page_tail();
?>