development.dbk

bochs : one pc simulator.

</section>
<section>
<title>
        Extent
</title>
<para>
	 &FIXME;
</para>
</section>
</section>

<section>
<title>Parameters
</title>
<para>
The following tables shows what parameters are used when creating redologs or creating "growing" images :
<table>   
<title>
        How number of entries in the catalog and number of blocks by extents are computed
</title>
<tgroup cols="5">
<thead>
<row>
<entry>Catalog entries</entry> <entry>Catalog size(KiB)</entry> <entry>Bitmap size (B)</entry> <entry>Extent size (KiB)</entry> <entry>Disk Max Size</entry>
</row>
</thead>

<tbody>
<row>
<entry>512</entry> <entry>2</entry> <entry>1</entry> <entry>4</entry> <entry>2MiB</entry>
</row>
<row>
<entry>512</entry> <entry>2</entry> <entry>2</entry> <entry>8</entry> <entry>4MiB</entry>
</row>
<row>
<entry>1k</entry> <entry>4</entry> <entry>2</entry> <entry>8</entry> <entry>8MiB</entry>
</row>
<row>
<entry>1k</entry> <entry>4</entry> <entry>4</entry> <entry>16</entry> <entry>16MiB</entry>
</row>
<row>
<entry>2k</entry> <entry>8</entry> <entry>4</entry> <entry>16</entry> <entry>32MiB</entry>
</row>
<row>
<entry>2k</entry> <entry>8</entry> <entry>8</entry> <entry>32</entry> <entry>64MiB</entry>
</row>
<row>
<entry>4k</entry> <entry>16</entry> <entry>8</entry> <entry>32</entry> <entry>128MiB</entry>
</row>
<row>
<entry>4k</entry> <entry>16</entry> <entry>16</entry> <entry>64</entry> <entry>256MiB</entry>
</row>
<row>
<entry>8k</entry> <entry>32</entry> <entry>16</entry> <entry>64</entry> <entry>512MiB</entry>
</row>
<row>
<entry>8k</entry> <entry>32</entry> <entry>32</entry> <entry>128</entry> <entry>1GiB</entry>
</row>
<row>
<entry>16k</entry> <entry>64</entry> <entry>32</entry> <entry>128</entry> <entry>2GiB</entry>
</row>
<row>
<entry>16k</entry> <entry>64</entry> <entry>64</entry> <entry>256</entry> <entry>4GiB</entry>
</row>
<row>
<entry>32k</entry> <entry>128</entry> <entry>64</entry> <entry>256</entry> <entry>8GiB</entry>
</row>
<row>
<entry>32k</entry> <entry>128</entry> <entry>128</entry> <entry>512</entry> <entry>16GiB</entry>
</row>
<row>
<entry>64k</entry> <entry>256</entry> <entry>128</entry> <entry>512</entry> <entry>32GiB</entry>
</row>
<row>
<entry>64k</entry> <entry>256</entry> <entry>256</entry> <entry>1024</entry> <entry>64GiB</entry>
</row>
<row>
<entry>128k</entry> <entry>512</entry> <entry>256</entry> <entry>1024</entry> <entry>128GiB</entry>
</row>
<row>
<entry>128k</entry> <entry>512</entry> <entry>512</entry> <entry>2048</entry> <entry>256GiB</entry>
</row>
<row>
<entry>256k</entry> <entry>1024</entry> <entry>512</entry> <entry>2048</entry> <entry>512GiB</entry>
</row>
<row>
<entry>256k</entry> <entry>1024</entry> <entry>1024</entry> <entry>4096</entry> <entry>1TiB</entry>
</row>
<row>
<entry>512k</entry> <entry>2048</entry> <entry>1024</entry> <entry>4096</entry> <entry>2TiB</entry>
</row>
<row>
<entry>512k</entry> <entry>2048</entry> <entry>2048</entry> <entry>8192</entry> <entry>4TiB</entry>
</row>
<row>
<entry>1024k</entry> <entry>4096</entry> <entry>2048</entry> <entry>8192</entry> <entry>8TiB</entry>
</row>
<row>
<entry>1024k</entry> <entry>4096</entry> <entry>4096</entry> <entry>16384</entry> <entry>16TiB</entry>
</row>
<row>
<entry>2048k</entry> <entry>8192</entry> <entry>4096</entry> <entry>16384</entry> <entry>32TiB</entry>
</row>
</tbody>
</tgroup>
</table>
</para>

</section>

<section>
<title>
        Redolog class description
</title>
<para>
The class <emphasis>redolog_t();</emphasis> implements the necessary
methods to create, open, close, read and write data to a redolog.
Managment of header catalog and sector bitmaps is done internally
by the class.
</para>
<section>
<title>
        Constants
</title>
<para>
<screen>
#define STANDARD_HEADER_MAGIC     "Bochs Virtual HD Image"
#define STANDARD_HEADER_VERSION   (0x00010000)
#define STANDARD_HEADER_SIZE      (512)
</screen>
These constants are used in the generic part of the header.
</para>

<para>
<screen>
#define REDOLOG_TYPE "Redolog"
#define REDOLOG_SUBTYPE_UNDOABLE "Undoable"
#define REDOLOG_SUBTYPE_VOLATILE "Volatile"
#define REDOLOG_SUBTYPE_GROWING  "Growing"
</screen>
These constants are used in the specific part of the header.
</para>

<para>
<screen>
#define REDOLOG_PAGE_NOT_ALLOCATED (0xffffffff)
</screen>
This constant is used in the catalog for an unwritten extent.
</para>

</section> <!-- Constants -->

<section> <title>Methods</title>
<para>
<emphasis>redolog_t();</emphasis> instanciates a new redolog.
</para>
<para>
<emphasis>int make_header (const char* type, Bit64u size);</emphasis> creates a header 
structure in memory, and sets its <emphasis>type</emphasis> and parameters based on the
disk image <emphasis>size</emphasis>. Returns 0.
</para>
<para>
<emphasis>int create (const char* filename, const char* type, Bit64u size);</emphasis> 
creates a new empty redolog file, with header and catalog, named <emphasis>filename</emphasis>
of type <emphasis>type</emphasis> for a <emphasis>size</emphasis> bytes image.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int create (int filedes, const char* type, Bit64u size);</emphasis>
creates a new empty redolog file, with header and catalog, in a previously 
opened file described by <emphasis>filedes</emphasis>, of type <emphasis>type</emphasis> 
for a <emphasis>size</emphasis> bytes image.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>int open (const char* filename, const char* type, Bit64u size);</emphasis>
opens a redolog file named <emphasis>filename</emphasis>, and checks
for consistency of header values against a <emphasis>type</emphasis> and
<emphasis>size</emphasis>.
Returns 0 for OK or -1 if a problem occured.
</para>
<para>
<emphasis>void close ();</emphasis>
closes a redolog file.
</para>
<para>
<emphasis>off_t lseek (off_t offset, int whence);</emphasis>
seeks at logical data offset <emphasis>offset</emphasis> in a redolog.
<emphasis>offset</emphasis> must be a multiple of 512.
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the redolog.
</para>
<para>
<emphasis>ssize_t read (void* buf, size_t count);</emphasis>
reads <emphasis>count</emphasis> bytes of data of the redolog, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read, that can be 0 if the data
has not previously be written to the redolog.
</para>
<para>
<emphasis>ssize_t write (const void* buf, size_t count);</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the redolog, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
</para>

</section> 

</section> <!-- Redolog class description -->

<section>
<title>
        Disk image classes description
</title>
<para>
"volatile" and "undoable" disk images are easily implemented
by instanciating a <emphasis>default_image_t</emphasis> object (flat image) 
and a <emphasis>redolog_t</emphasis> object (redolog).
</para>
<para>
"growing" disk images only instanciates a <emphasis>redolog_t</emphasis> object.
</para>
<para>
Classe names are <emphasis>undoable_image_t</emphasis>, <emphasis>volatile_image_t</emphasis>
and <emphasis>growing_image_t</emphasis>.
</para>
<para>
When using these disk images, the underlying data structure and layout
is completely
hidden to the caller. Then, all offset and size values are "logical" values,
as if the disk was a flat file.
</para>
<section>
<title>
        Constants
</title>
<para>
<screen>
#define UNDOABLE_REDOLOG_EXTENSION ".redolog"
#define UNDOABLE_REDOLOG_EXTENSION_LENGTH (strlen(UNDOABLE_REDOLOG_EXTENSION))
#define VOLATILE_REDOLOG_EXTENSION ".XXXXXX"
#define VOLATILE_REDOLOG_EXTENSION_LENGTH (strlen(VOLATILE_REDOLOG_EXTENSION))
</screen>
These constants are used when building redolog file names
</para>
</section>

<section>
<title>
        undoable_image_t methods
</title>
<para>
<emphasis>
undoable_image_t(Bit64u size, const char* redolog_name);
</emphasis>
instanciates a new <emphasis>undoable_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes and
the redolog filename is <emphasis>redolog_name</emphasis>. 
</para>

<para>
<emphasis>
int open (const char* pathname);
</emphasis>
opens the flat disk image <emphasis>pathname</emphasis>,
as an undoable disk image. The associated redolog will
be named <emphasis>pathname</emphasis> with a 
<emphasis>UNDOABLE_REDOLOG_EXTENSION</emphasis>
suffix, unless set in the constructor.
Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close ();
</emphasis>
closes the flat image and its redolog.
</para>

<para>
<emphasis>
off_t lseek (off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the undoable disk image. 
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical
offset in the undoable disk image.
</para>

<para>
<emphasis>
ssize_t read (void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data 
from the undoable disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
Data will be read from the redolog if it has
been previously written or from the flat image
otherwise.
</para>

<para>
<emphasis>
ssize_t write (const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the undoable disk image, at current logical offset.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes written.
Data will always be written to the redolog.
</para>
</section>

<section>
<title>
        volatile_image_t methods
</title>
<para>
<emphasis>
volatile_image_t(Bit64u size, const char* redolog_name);
</emphasis>
instanciates a new <emphasis>volatile_image_t</emphasis>
object. This disk image logical length is <emphasis>size</emphasis> bytes and
the redolog filename is <emphasis>redolog_name</emphasis> plus a 
random suffix. 
</para>

<para>
<emphasis>
int open (const char* pathname);
</emphasis>
opens the flat disk image <emphasis>pathname</emphasis>,
as a volatile disk image. The associated redolog will
be named <emphasis>pathname</emphasis> with a 
random suffix, unless set in the constructor.
Returns 0 for OK or -1 if a problem occured.
</para>

<para>
<emphasis>
void close ();
</emphasis>
closes the flat image and its redolog.
The redolog is deleted/lost after close is called.
</para>

<para>
<emphasis>
off_t lseek (off_t offset, int whence);
</emphasis>
seeks at logical data position <emphasis>offset</emphasis> in
the volatile disk image. 
Only SEEK_SET is supported for <emphasis>whence</emphasis>.
Returns -1 if a problem occured, or the current logical offset in
the volatile disk image.
</para>

<para>
<emphasis>
ssize_t read (void* buf, size_t count);
</emphasis>
reads <emphasis>count</emphasis> bytes of data 
from the volatile disk image, from current logical offset,
and copies it into <emphasis>buf</emphasis>.
<emphasis>count</emphasis> must be 512.
Returns the number of bytes read.
Data will be read from the redolog if it has
been previously written or from the flat image
otherwise.
</para>

<para>
<emphasis>
ssize_t write (const void* buf, size_t count);
</emphasis>
writes <emphasis>count</emphasis> bytes of data from <emphasis>buf</emphasis> 
to the volatile disk image,