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@c Copyright (c) 2002 Kungliga Tekniska H�gskolan
@c (Royal Institute of Technology, Stockholm, Sweden).
@c All rights reserved.
@c $arla: prog-disco.texi,v 1.1 2002/05/27 13:08:31 lha Exp $
@cindex Disconected operation
@chapter Disco with arla
Disconnected operation of arla.
@section The Log
The binary log is written to a file. All entries are of variable size.
A entry is never removed from the log @pxref{Log entry optimization}.
@subsection One log entry
One log entry consists of a log header with magic cookie, opcode,
checksum, and length. The entry is is always 4 byte aligned in the
logfile. The checksum is a simple one, its just to verify that for
data corruption hasn't occured and to make sure the entry is a valid
one.
@subsection Disconnected vs connected nodes
A FCacheNode is either a @dfn{disconnected node} or a @dfn{connected
node}. The later means that the node was created when arla was in
connected mode and thus (potentially) exist on the file server.
A disconnected node on the other hand was created when is disconnected
operation. A disconnected node always have one or more entries in the
log.
@subsection Log entry offset
The offset of the entry, a unsigned 32 bit number, is called
@dfn{disco_id}. Its stored in the FCacheNode so it can be updated when
there is a operation on this node. All nodes for a FCacheEntry are
single linked list (from the newest log entry to the oldest), the
optimizer uses this to modify all previous entries from a FCacheNode.
A FCacheNode with disco_id equal to 0 is a connected node that there
have been no disconnected operation made on.
The first entry in the log is a nop entry to make sure not a
log-offset that is for a ``real'' entry.
The limit of number of entries in the log are 2^32 / the size of the
largest entry since the offset is a 32 bit number.
@c @subsection Dump log / Backup of log
@c
@c It should be possible to extract a dump of the current state of
@c disconnected operation (all adding operations that is). This is to
@c make a backup of all changes before reitegration.
@section Log entry optimization
@anchor{Log entry optimization}
To try to preserve bandwith when reinterating there are dependencies
between entries. First we try to avoid storing data to the fileserver
that was never meant to got there. For example a file that was created
and then removed in disconnected mode, ie @code{DISCO_HEADER_NOP} is
set in the flags field in the header.
@subsection Removal operations
When a node is removed and the node is a disconnected node, the all
previous entries are optizmied away by setting a flags in their entry
headers. This make this entry/nodes be ignored by the reintergration
code and never commited to the fileserver.
@subsection Moveing a disconnected node
If a disconnected node is moved, it will be created in the target
directory instead of first being created and then moved.
@subsection Storestatus and storedata
Also, all entries for one node storestate/storestatus are compressed
to one createnode (and if needed storedata).
@section data storage
@subsection common data types
fid - VenusFid equivalent
storestatus - AFSStoreStatus equivalent
@enumerate
@item
@code{nop}
needs to be smaller or equal in size then the rest
data storage:
header
flags
fid
@item
@code{storedata}
(truncation is a storedata)
data storage:
header
fid
storestatus
size
@item
@code{storestatus}
data storage:
header
fid
storestatus
@item
@code{createfile}
data storage:
header
parentfid
fid
storestatus
name[AFSNAMEMAX]
@item
@code{createsymlink}
data storage:
header
parentfid
fid
storestatus
name[AFSNAMEMAX]
targetname[AFSNAMEMAX]
@item
@code{createlink}
data storage:
header
parentfid
fid
storestatus
name[AFSNAMEMAX]
targetfid
@item
@code{unlink}
data storage:
header
parentfid
fid /* dup info */
name[AFSNAMEMAX]
@item
@code{createdir}
data storage:
header
parentfid
fid /* dup info */
storestatus
name[AFSNAMEMAX]
@item
@code{removedir}
data storage:
header
parentfid
fid /* dup info */
name[AFSNAMEMAX]
@end enumerate
@section reintegration
@subsection Cook-book
@enumerate
@item
make sure first entry in the log is a nop entry
@item
if nop entry or @code{DISCO_HEADER_NOP} is set, continue to next
@item
the parent fid is transformed to a connected fid (if needed)
it this failes, we are unhappy and save this node for collision
recovery
@item
the fid is transformed to a connected fid (if needed)
it this failes, we are unhappy and save this node for collision
recovery
@item
operation is performed
@item
if there is change on a fid
@enumerate
@item
update kernelhandle
@item
update fcachehandle
@item
update directory fid for this name (if needed)
@item
transformed fids are stored in the transformation table
@end enumerate
@end enumerate
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