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NOTE: This file is very out of date.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