[OpenAFS-devel] DNS and Freelance features for Windows clients
Jeff Riegel
riegel@almaden.ibm.com
Tue, 2 Oct 2001 22:10:44 -0700
I have just submitted a patch to the gatekeepers. This patch provides
two new features for the Windows clients: DNS lookup of AFSDB records
(as already available for the Unix clients) and an experimental feature
called "Freelance client". The Freelance client avoids the need for
a home cell and stores the mount points for the AFS root directory in
a file on the client's local filesystem. Mount points can be added or
deleted by the user using the Explorer shell extension or by the standard
fs commands "mkmount" and "rmmount". These new features can be selectively
compiled in by defining the macros "AFS_AFSDB_ENV" for the DNS feature and
"AFS_FREELANCE_CLIENT" for the Freelance feature.
This work was done primarily by two former summer students here at IBM
Almaden, Yee-jiun Song (Freelance) and Ahmed Amer (DNS). I have done
some further editing and integration.
This code is still experimental, and we are interested in any feedback.
Please try out these features and send any comments or problem reports
to the mailing list. A binary release incorporating the new code will
be available soon.
The following technical description of the new features has also been
placed in a new file called "NewFeatures-WIN" in the src directory.
Jeff Riegel
riegel@almaden.ibm.com
New features for the Windows Clients
------------------------------------
This file describes new features that have been added to the Windows AFS
clients.
DNS lookup
----------
DNS lookup of cell servers is now available for the Windows AFS clients.
A type 1 AFSDB record is queried to determine the cell server host names.
These names are then resolved to IP addresses.
1. Usage
This feature is enabled at compilation with the switch "AFS_AFSDB_ENV",
as with the Unix clients. It is activated by default, and can be disabled
at runtime by running afsd.exe with the -noafsdb flag for the Win9x client,
or by setting the following registry entry on the NT/2000 client:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TransarcAFSDaemon\Parameters\UseDNS=0
The Windows AFS clients use a configuration file named afsdns.ini (stored in
the same directory as the cell server database) to determine the address
of the DNS server. This file has the following format:
[AFS Domain Name Servers]
ns1=xx.xx.xx.xx
Only one name server is actually used currently. Support for multiple
name servers should be easy to add.
2. Design
Because of the lack of standard resolver libraries on the Win32 and DJGPP
platforms, it was decided to perform DNS queries by manually creating
packets to send to the DNS server. The DNS response is then decoded to
determine the correct cell server addresses.
New files:
WINNT/afsd/cm_dns.c
WINNT/afsd/cm_dns.h
WINNT/afsd/cm_dns_private.h
Changed files:
WINNT/afsd/cm_config.c
WINNT/afsd/cm_cell.c
WINNT/afsd/cm_ioctl.c
WINNT/afsd/afsd_init.c
WINNT/afsd/afsd_init95.c
auth/cellconfig.c
kauth/user_nt.c
3. Future work
Support for multiple DNS servers
Support for resolver libraries, if available for DJGPP and/or Win32
Freelance AFS Client
--------------------
1 Introduction
The current implementation of AFS requires that all AFS clients belong to
a home cell. The home cell provides the client with a starting point to
mount the entire AFS file system. The client's top most level view of AFS
is determined by the home cell server's root.afs volume. Through root.afs,
the home cell also controls which cells clients can access.
To provide a more flexible and relevant view of the AFS file system to the
user, this projects aims to remove the need for a home cell and to allow
each client to customize its view of the AFS file system. To this end,
the current Windows 2000 and 9x clients for AFS have been modified into
a Freelance AFS Client that allows the user to mount and dismount AFS
cells at will, without the need of a home cell.
The new Freelance AFS Client also increases the scalability of the AFS file
system since administrator intervention is no longer required for clients
to access newly established cells. It also removes the client dependency on
the availability of the home cell. Previously, if the home cell were not
available, clients would not be able to access the AFS file system. This
critical dependency is not present in the Freelance AFS Client.
2 Usage
The Freelance feature is available only for the Windows NT/2000 and 9x
clients. In 9x, it can be enabled by running afsd.exe manually with the
"-freelance" flag. It can be enabled in NT/2000 by setting the following
registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TransarcAFSDaemon\Parameters\FreelanceClient=1
(GUI support to activate this feature will be available soon.)
The Freelance client reads the available mount points from a file called
afs_freelance.ini. This file will be created if not found and the list
of mount points will initially be empty. New mount points can be added
using "fs mkmount" or the Explorer shell extension.
Specification of a home cell is unnecessary with the Freelance client
itself, but is still needed by programs such as klog and pts to provide
a default cell argument.
3 Design
This section describes the design approach and provides a high-level
description of the project.
3.1 Design Approach
The main aim of the project was to shift the client's view of the AFS file
system, root.afs, from the home cell onto the client, and thus eliminate the
need for a home cell. This had to be done while maintaining compatibility
with the existing system, so changes to the client were kept to a minimum.
My primary approach has been to trick the current system into thinking
that there is still a home cell by while feeding it fake information that
is generated from a locally stored root.afs directory whenever root.afs of
the home cell is requested. This is accomplished by intercepting function
calls that fetch data from root.afs on the home cell.
3.2 Afs_freelance.ini
The local version of root.afs is represented by a file named
afs_freelance.ini, typically stored in the same directory as the cell
database. The first line of this file is an integer that specifies the
number of mount points there are in this file. The rest of the file is a
list of entries, one on each line, in the form xxx#yyy:zzz, where xxx is the
name of the mount point, yyy is the cell name and zzz is the volume name.
3.3 Directory File Structure
Using the data in afs_freelance.ini, a fake directory is created in memory that
is identical to what an AFS directory containing those mount points. This
fake directory is then fed to the client when necessary. The structure
of the directory is as follows:
1. Each directory is made up of pages, each of a fixed size.
2. Each page is divided into 32 byte chunks, which are indivisible units.
3. The first 13 chunks of the first page, called the directory header page,
are used for header information.
4. The first chunk of all other pages, are also used for header information.
5. Chunks other than those reserved for header information can be used
to store mount points. Mount points are stored in a struct defined as such:
typedef struct cm_localMountPoint {
char* namep;
char* mountPointStringp;
struct cm_localMountPoint* next;
} cm_localMountPoint_t;
3.4 Adding/removing mounts
The fs commands "mkmount" and "rmmount" can be used to add/remove mount
points from the afs_freelance.ini file. These functions can also be
accessed from the Explorer shell extension.
4 Implementation
4.1 Files Changed/Added
Most of the changes have been made in 5 files:
afsd_init.c
cm_callback.c
cm_dcache.c
cm_scache.c
cm_vnodeops.c
Afsd_init.c was changed to include initialization code for the fake
directory and local mount points. Cm_callback.c was changed to handle
callbacks to /afs differently, since it is now local. Cm_dcache was
changed to feed fake information into buffers when the /afs directory is
read. Cm_scache.c was changed to provide fake scp information for the
mount points found under /afs. Finally, cm_vnodeops.c was modified to
make the function trybulkproc skip the fake directory entries.
In addition, the following files were added:
cm_freelance.h
cm_freelance.c
Cm_freelance.h and cm_freelance.c were added to provide functions that
create and handle the fake directory and fake mount points.
4.2 Functions Modified
Below is a list of the functions that have been modified. The list is
not exhaustive but includes most of the major changes.
4.2.1 afsd_InitCM
Several lines of code were added to this function to call the initialization
functions for the fake directory and fake mount points.
4.2.2 cm_HaveCallback
This function is called to check if files have changed. The /afs directory
and mount points on /afs need to handled differently by this function. In
particular, whenever this function is called on mount points on /afs,
the function needs to always return true. This is because local mount
points are only added or removed, never modified.
4.2.3 cm_GetCallBack
Because of the same reasons as in 4.2.2, this function needs to handle
/afs differently. This function should never be called on the local mount
points since the cm_HaveCallBack function always returns true on local
mount points. When this function is called on /afs, we need to load the
status information of /afs if it is the first time that /afs is accessed
since initialization of the fake directory. Otherwise, we simply return.
4.2.4 cm_GetBuffer
This function is used to fetch actual data from a file into memory
buffers. When this function is called on /afs, we need to fill the memory
buffers with data from the fake directory created in memory, rather than
by calling server functions.
4.2.5 cm_GetSCache
This function is used to fetch meta data about files. When it is called
on /afs, we return a hardcoded scache structure. When it is called on
the mount points on /afs, we return fake scache data based on the mount
points in afs_freelance.ini
4.2.6 cm_SyncOp
This function was modified to skip cm_HaveCallback and cm_GetCallback
calls on the mount points on /afs.
4.2.6 cm_MergeStatus
This function was modified to provide fake status data on /afs.
4.2.7 cm_TryBulkProc
This function was modified to skip operations on fake mount points.
4.3 New Functions
4.3.1 cm_InitFakeRootDir
This function uses the array cm_localMountPoints and creates in memory
an image of a fake directory. This directory is then used to fill buffers
when read requests of /afs are made.
4.3.2 cm_getNoLocalMountPoints
This function returns the number of mount points on /afs, based on
afs_freelance.ini.
4.3.3 cm_InitLocalMountPoints
This function reads afs_freelance.ini and creates an array of fake mount points
based on its contents. The array is then used by cm_InitFakeRootDir to
create a fake directory in memory.
4.3.4 reInitLocalMountPoints
This function clears all the fake information in memory and reconstructs
them from afs_freelance.ini.
5 Current Status
This feature is still experimental. Please post problem reports to
the openafs-devel mailing list.
5.1 Future Work
GUI support for activation of the Freelance feature will be available soon.
An auto-mount function could be added. This would work by intercepting
the cm_lookup call so that when a cell is not found in /afs, it would be
automatically added.
Support for Unix clients.