path: root/docs/package-set.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">

<chapter id="file-format">
  <title>Package Set File Format</title>
  
  <sect2 id="file-header">
    <title>File header</title>
    
    <para>
      The repo starts with a header, containing some number of
      sections, terminated by a section with type 0:
    </para>

    <programlisting><![CDATA[
struct razor_set_header {
	uint32_t magic;
	uint32_t version;
	struct razor_set_section sections[0];
};

struct razor_set_section {
	uint32_t type;
	uint32_t offset;
	uint32_t size;
};
]]></programlisting>

    <para>
      razor_set_open() mmaps the repo file, and creates a struct razor_set:
    </para>

    <programlisting><![CDATA[
struct razor_set {
	struct array string_pool;
 	struct array packages;
 	struct array properties;
 	struct array files;
	struct array package_pool;
 	struct array property_pool;
 	struct array file_pool;
	struct razor_set_header *header;
};
]]></programlisting>

    <para>
      by finding the sections with those IDs and creating struct
      array's pointing to the right places in the mmapped data. (This
      is the only processing needed when reading in the file;
      everything else is used exactly as-is.)
    </para>

  </sect2>

  <sect2 id="sections">
    <title>The sections</title>

    <itemizedlist>
      <listitem>
        <para>
          <emphasis>RAZOR_STRING_POOL</emphasis> Stores one copy of
	  each string that appears in the repo. (At the moment, this
	  is: package names, package versions, property names,
	  property versions, and (basenames of) filenames.) The
	  strings are arbitrarily-sized, 0-terminated, and not in any
	  particular order (although the empty string always ends up
	  being at offset 0).
	</para>
      </listitem>

      <listitem>
        <para>
          <emphasis>RAZOR_PACKAGES</emphasis> Array of struct
	  razor_package; one for each package in the set, sorted by
	  name.
	</para>
      </listitem>

      <listitem>
        <para>
          <emphasis>RAZOR_PROPERTIES</emphasis> Array of struct
	  razor_property; one for each unique property in the set,
	  sorted by type, then name, then relation type (eg, "&lt;" or
	  "&gt;="), then version. (Properties with no version have
	  relation type RAZOR_VERSION_EQUAL, and version "".)
	</para>
      </listitem>
	    
      <listitem>
        <para>
          <emphasis>RAZOR_FILES</emphasis> Array of struct
	  razor_entry; one for each file owned by any package in the
	  set. The current sort order (which is subject to change)
	  is breadth-first, sorted by basename. So eg: /, /bin,
	  /dev, /etc, /bin/false, /bin/true, /dev/null, /etc/passwd.
	</para>
      </listitem>

      <listitem>
        <para>
          <emphasis>RAZOR_PACKAGE_POOL</emphasis> Array of struct
	  list, with each list item containing the index of a struct
	  razor_package in the packages section. See the discussion
	  of lists below.
	</para>
      </listitem>

      <listitem>
        <para>
          <emphasis>RAZOR_PROPERTY_POOL</emphasis> Array of struct
	  list, with each list item containing the index of a struct
	  razor_property in the properties section. See the
	  discussion of lists below.
	</para>
      </listitem>

      <listitem>
        <para>
          <emphasis>RAZOR_FILE_POOL</emphasis> Array of struct list,
	  with each list item containing the index of a struct
	  razor_entry in the files section. See the discussion of
	  lists below.
	</para>
      </listitem>
    </itemizedlist>
  </sect2>

  <sect2 id="data-types">
    <title>Data types</title>

    <para>
      Note that the exact layout of bits involves some historical
      accidents.  (Particularly the fact that the "name" field in most
      structs loses its high bits to a flags field.)
    </para>

    <programlisting><![CDATA[
struct list_head
	uint list_ptr : 24;
	uint flags    : 8;

struct list
	uint data  : 24;
	uint flags : 8;
]]></programlisting>

    <para>
      Used to store lists of package, property, or file IDs. "struct
      list_head" stores the head of the list, which points to one or
      more "struct list"s in the appropriate "pool" section.  ("struct
      list" should probably be called "struct list_item".)
    </para>

    <para>
      "list_first(&amp;head, &amp;pool)" returns a "struct list *"
      pointing to the first element of the list (or NULL for an empty
      list), and "list_next(list)" will return successive elements,
      until NULL is returned. Each "list->data" contains the index of
      a package, property, or file in the corresponding section of the
      set.
    </para>

    <para>
      Peeking underneath the abstraction, a list_head's "flags" is
      0xff if the list is empty, 0x80 if it contains a single element,
      or 0x00 if it contains more than one element. In the
      single-element case, that element is actually stored in the
      list_head directly rather than being stored in a pool (and so
      list_first() just casts the list_head* to a list* and returns
      it). For multi-element lists, list_ptr is the index in the pool
      of the first element of this list; the list continues through
      successive elements of the pool until one with non-zero flags is
      reached, indicating the end of the list.
    </para>

    <programlisting><![CDATA[
struct razor_package
	uint name    : 24;
	uint flags   : 8;
	uint version : 32;
	struct list_head properties;
	struct list_head files;
]]></programlisting>

    <para>
      name and version are indexes into string_pool. properties is a
      list of all of the package's properties, and files is a list of
      its files. flags is currently only used during razor_set
      merging, to keep track of which set a package came from.
    </para>

    <programlisting><![CDATA[
struct razor_property
	uint name     : 24;
	uint flags    : 6;
	uint type     : 2;
	uint relation : 32;
	uint version  : 32;
	struct list_head packages;
]]></programlisting>

    <para>
      name and version are indexes into string_pool. type is an enum
      razor_property_type (eg, RAZOR_PROPERTY_REQUIRES), and relation
      is an enum razor_version_relation (eg,
      RAZOR_VERSION_GREATER_OR_EQUAL). packages is a list of the
      packages that have this property. flags is currently unused.
    </para>

    <programlisting><![CDATA[
struct razor_entry
	uint name  : 24;
	uint flags : 8;
	uint start : 32;
	struct list_head packages;
]]></programlisting>

    <para>
      name is an index into string_pool, giving the basename of the
      file. start is either 0, or an index pointing to another
      razor_entry that is the first child of this entry (for a
      non-empty directory). (Entry 0 is always the root of the tree,
      so no entry could have entry 0 as a child.) flags is 0x80
      (RAZOR_ENTRY_LAST) if an entry is the last entry in its
      directory. Otherwise it is 0.
    </para>

    <para>
      Note that given a pointer to a struct_razor_entry (eg, from a
      package's "files" list), there is no way to reconstruct its full
      name without walking the entire files array up to that
      point. Because of this and other problems (fix_file_map()), it
      seems like razor_entry should be modified to include a pointer
      to its parent. (Storing full paths instead of just basenames
      would also fix this problem, but that would use much more
      memory.)
    </para>
  </sect2>
</chapter>