NOTE: 
  This is one of the technical documents describing a component of
  Coda -- this document describes the client kernel-Venus interface.
  
  For more information:
    http://www.coda.cs.cmu.edu
  For user level software needed to run Coda:
    ftp://ftp.coda.cs.cmu.edu
  
  To run Coda you need to get a user level cache manager for the client,
  named Venus, as well as tools to manipulate ACLs, to log in, etc.  The
  client needs to have the Coda filesystem selected in the kernel
  configuration.
  
  The server needs a user level server and at present does not depend on
  kernel support.
  
  
  
  
  
  
  
    The Venus kernel interface
    Peter J. Braam
    v1.0, Nov 9, 1997
  
    This document describes the communication between Venus and kernel
    level filesystem code needed for the operation of the Coda file sys-
    tem.  This document version is meant to describe the current interface
    (version 1.0) as well as improvements we envisage.
    ______________________________________________________________________
  
    Table of Contents
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    1. Introduction
  
    2. Servicing Coda filesystem calls
  
    3. The message layer
  
       3.1 Implementation details
  
    4. The interface at the call level
  
       4.1 Data structures shared by the kernel and Venus
       4.2 The pioctl interface
       4.3 root
       4.4 lookup
       4.5 getattr
       4.6 setattr
       4.7 access
       4.8 create
       4.9 mkdir
       4.10 link
       4.11 symlink
       4.12 remove
       4.13 rmdir
       4.14 readlink
       4.15 open
       4.16 close
       4.17 ioctl
       4.18 rename
       4.19 readdir
       4.20 vget
       4.21 fsync
       4.22 inactive
       4.23 rdwr
       4.24 odymount
       4.25 ody_lookup
       4.26 ody_expand
       4.27 prefetch
       4.28 signal
  
    5. The minicache and downcalls
  
       5.1 INVALIDATE
       5.2 FLUSH
       5.3 PURGEUSER
       5.4 ZAPFILE
       5.5 ZAPDIR
       5.6 ZAPVNODE
       5.7 PURGEFID
       5.8 REPLACE
  
    6. Initialization and cleanup
  
       6.1 Requirements
  
  
    ______________________________________________________________________
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    11..  IInnttrroodduuccttiioonn
  
  
  
    A key component in the Coda Distributed File System is the cache
    manager, _V_e_n_u_s.
  
  
    When processes on a Coda enabled system access files in the Coda
    filesystem, requests are directed at the filesystem layer in the
    operating system. The operating system will communicate with Venus to
    service the request for the process.  Venus manages a persistent
    client cache and makes remote procedure calls to Coda file servers and
    related servers (such as authentication servers) to service these
    requests it receives from the operating system.  When Venus has
    serviced a request it replies to the operating system with appropriate
    return codes, and other data related to the request.  Optionally the
    kernel support for Coda may maintain a minicache of recently processed
    requests to limit the number of interactions with Venus.  Venus
    possesses the facility to inform the kernel when elements from its
    minicache are no longer valid.
  
    This document describes precisely this communication between the
    kernel and Venus.  The definitions of so called upcalls and downcalls
    will be given with the format of the data they handle. We shall also
    describe the semantic invariants resulting from the calls.
  
    Historically Coda was implemented in a BSD file system in Mach 2.6.
    The interface between the kernel and Venus is very similar to the BSD
    VFS interface.  Similar functionality is provided, and the format of
    the parameters and returned data is very similar to the BSD VFS.  This
    leads to an almost natural environment for implementing a kernel-level
    filesystem driver for Coda in a BSD system.  However, other operating
    systems such as Linux and Windows 95 and NT have virtual filesystem
    with different interfaces.
  
    To implement Coda on these systems some reverse engineering of the
    Venus/Kernel protocol is necessary.  Also it came to light that other
    systems could profit significantly from certain small optimizations
    and modifications to the protocol. To facilitate this work as well as
    to make future ports easier, communication between Venus and the
    kernel should be documented in great detail.  This is the aim of this
    document.
  
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    22..  SSeerrvviicciinngg CCooddaa ffiilleessyysstteemm ccaallllss
  
    The service of a request for a Coda file system service originates in
    a process PP which accessing a Coda file. It makes a system call which
    traps to the OS kernel. Examples of such calls trapping to the kernel
    are _r_e_a_d_, _w_r_i_t_e_, _o_p_e_n_, _c_l_o_s_e_, _c_r_e_a_t_e_, _m_k_d_i_r_, _r_m_d_i_r_, _c_h_m_o_d in a Unix
    context.  Similar calls exist in the Win32 environment, and are named
    _C_r_e_a_t_e_F_i_l_e_, .
  
    Generally the operating system handles the request in a virtual
    filesystem (VFS) layer, which is named I/O Manager in NT and IFS
    manager in Windows 95.  The VFS is responsible for partial processing
    of the request and for locating the specific filesystem(s) which will
    service parts of the request.  Usually the information in the path
    assists in locating the correct FS drivers.  Sometimes after extensive
    pre-processing, the VFS starts invoking exported routines in the FS
    driver.  This is the point where the FS specific processing of the
    request starts, and here the Coda specific kernel code comes into
    play.
  
    The FS layer for Coda must expose and implement several interfaces.
    First and foremost the VFS must be able to make all necessary calls to
    the Coda FS layer, so the Coda FS driver must expose the VFS interface
    as applicable in the operating system. These differ very significantly
    among operating systems, but share features such as facilities to
    read/write and create and remove objects.  The Coda FS layer services
    such VFS requests by invoking one or more well defined services
    offered by the cache manager Venus.  When the replies from Venus have
    come back to the FS driver, servicing of the VFS call continues and
    finishes with a reply to the kernel's VFS. Finally the VFS layer
    returns to the process.
  
    As a result of this design a basic interface exposed by the FS driver
    must allow Venus to manage message traffic.  In particular Venus must
    be able to retrieve and place messages and to be notified of the
    arrival of a new message. The notification must be through a mechanism
    which does not block Venus since Venus must attend to other tasks even
    when no messages are waiting or being processed.
  
  
  
  
  
  
                       Interfaces of the Coda FS Driver
  
    Furthermore the FS layer provides for a special path of communication
    between a user process and Venus, called the pioctl interface. The
    pioctl interface is used for Coda specific services, such as
    requesting detailed information about the persistent cache managed by
    Venus. Here the involvement of the kernel is minimal.  It identifies
    the calling process and passes the information on to Venus.  When
    Venus replies the response is passed back to the caller in unmodified
    form.
  
    Finally Venus allows the kernel FS driver to cache the results from
    certain services.  This is done to avoid excessive context switches
    and results in an efficient system.  However, Venus may acquire
    information, for example from the network which implies that cached
    information must be flushed or replaced. Venus then makes a downcall
    to the Coda FS layer to request flushes or updates in the cache.  The
    kernel FS driver handles such requests synchronously.
  
    Among these interfaces the VFS interface and the facility to place,
    receive and be notified of messages are platform specific.  We will
    not go into the calls exported to the VFS layer but we will state the
    requirements of the message exchange mechanism.
  
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    33..  TThhee mmeessssaaggee llaayyeerr
  
  
  
    At the lowest level the communication between Venus and the FS driver
    proceeds through messages.  The synchronization between processes
    requesting Coda file service and Venus relies on blocking and waking
    up processes.  The Coda FS driver processes VFS- and pioctl-requests
    on behalf of a process P, creates messages for Venus, awaits replies
    and finally returns to the caller.  The implementation of the exchange
    of messages is platform specific, but the semantics have (so far)
    appeared to be generally applicable.  Data buffers are created by the
    FS Driver in kernel memory on behalf of P and copied to user memory in
    Venus.
  
    The FS Driver while servicing P makes upcalls to Venus.  Such an
    upcall is dispatched to Venus by creating a message structure.  The
    structure contains the identification of P, the message sequence
    number, the size of the request and a pointer to the data in kernel
    memory for the request.  Since the data buffer is re-used to hold the
    reply from Venus, there is a field for the size of the reply.  A flags
    field is used in the message to precisely record the status of the
    message.  Additional platform dependent structures involve pointers to
    determine the position of the message on queues and pointers to
    synchronization objects.  In the upcall routine the message structure
    is filled in, flags are set to 0, and it is placed on the _p_e_n_d_i_n_g
    queue.  The routine calling upcall is responsible for allocating the
    data buffer; its structure will be described in the next section.
  
    A facility must exist to notify Venus that the message has been
    created, and implemented using available synchronization objects in
    the OS. This notification is done in the upcall context of the process
    P. When the message is on the pending queue, process P cannot proceed
    in upcall.  The (kernel mode) processing of P in the filesystem
    request routine must be suspended until Venus has replied.  Therefore
    the calling thread in P is blocked in upcall.  A pointer in the
    message structure will locate the synchronization object on which P is
    sleeping.
  
    Venus detects the notification that a message has arrived, and the FS
    driver allow Venus to retrieve the message with a getmsg_from_kernel
    call. This action finishes in the kernel by putting the message on the
    queue of processing messages and setting flags to READ.  Venus is
    passed the contents of the data buffer. The getmsg_from_kernel call
    now returns and Venus processes the request.
  
    At some later point the FS driver receives a message from Venus,
    namely when Venus calls sendmsg_to_kernel.  At this moment the Coda FS
    driver looks at the contents of the message and decides if:
  
  
    +o  the message is a reply for a suspended thread P.  If so it removes
       the message from the processing queue and marks the message as
       WRITTEN.  Finally, the FS driver unblocks P (still in the kernel
       mode context of Venus) and the sendmsg_to_kernel call returns to
       Venus.  The process P will be scheduled at some point and continues
       processing its upcall with the data buffer replaced with the reply
       from Venus.
  
    +o  The message is a _d_o_w_n_c_a_l_l.  A downcall is a request from Venus to
       the FS Driver. The FS driver processes the request immediately
       (usually a cache eviction or replacement) and when it finishes
       sendmsg_to_kernel returns.
  
    Now P awakes and continues processing upcall.  There are some
    subtleties to take account of. First P will determine if it was woken
    up in upcall by a signal from some other source (for example an
    attempt to terminate P) or as is normally the case by Venus in its
    sendmsg_to_kernel call.  In the normal case, the upcall routine will
    deallocate the message structure and return.  The FS routine can proceed
    with its processing.
  
  
  
  
  
  
  
                        Sleeping and IPC arrangements
  
    In case P is woken up by a signal and not by Venus, it will first look
    at the flags field.  If the message is not yet READ, the process P can
    handle its signal without notifying Venus.  If Venus has READ, and
    the request should not be processed, P can send Venus a signal message
    to indicate that it should disregard the previous message.  Such
    signals are put in the queue at the head, and read first by Venus.  If
    the message is already marked as WRITTEN it is too late to stop the
    processing.  The VFS routine will now continue.  (-- If a VFS request
    involves more than one upcall, this can lead to complicated state, an
    extra field "handle_signals" could be added in the message structure
    to indicate points of no return have been passed.--)
  
  
  
    33..11..  IImmpplleemmeennttaattiioonn ddeettaaiillss
  
    The Unix implementation of this mechanism has been through the
    implementation of a character device associated with Coda.  Venus
    retrieves messages by doing a read on the device, replies are sent
    with a write and notification is through the select system call on the
    file descriptor for the device.  The process P is kept waiting on an
    interruptible wait queue object.
  
    In Windows NT and the DPMI Windows 95 implementation a DeviceIoControl
    call is used.  The DeviceIoControl call is designed to copy buffers
    from user memory to kernel memory with OPCODES. The sendmsg_to_kernel
    is issued as a synchronous call, while the getmsg_from_kernel call is
    asynchronous.  Windows EventObjects are used for notification of
    message arrival.  The process P is kept waiting on a KernelEvent
    object in NT and a semaphore in Windows 95.
  
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    44..  TThhee iinntteerrffaaccee aatt tthhee ccaallll lleevveell
  
  
    This section describes the upcalls a Coda FS driver can make to Venus.
    Each of these upcalls make use of two structures: inputArgs and
    outputArgs.   In pseudo BNF form the structures take the following
    form:
  
  
    struct inputArgs {
        u_long opcode;
        u_long unique;     /* Keep multiple outstanding msgs distinct */
        u_short pid;                 /* Common to all */
        u_short pgid;                /* Common to all */
        struct CodaCred cred;        /* Common to all */
  
        <union "in" of call dependent parts of inputArgs>
    };
  
    struct outputArgs {
        u_long opcode;
        u_long unique;       /* Keep multiple outstanding msgs distinct */
        u_long result;
  
        <union "out" of call dependent parts of inputArgs>
    };
  
  
  
    Before going on let us elucidate the role of the various fields. The
    inputArgs start with the opcode which defines the type of service
    requested from Venus. There are approximately 30 upcalls at present
    which we will discuss.   The unique field labels the inputArg with a
    unique number which will identify the message uniquely.  A process and
    process group id are passed.  Finally the credentials of the caller
    are included.
  
    Before delving into the specific calls we need to discuss a variety of
    data structures shared by the kernel and Venus.
  
  
  
  
    44..11..  DDaattaa ssttrruuccttuurreess sshhaarreedd bbyy tthhee kkeerrnneell aanndd VVeennuuss
  
  
    The CodaCred structure defines a variety of user and group ids as
    they are set for the calling process. The vuid_t and guid_t are 32 bit
    unsigned integers.  It also defines group membership in an array.  On
    Unix the CodaCred has proven sufficient to implement good security
    semantics for Coda but the structure may have to undergo modification
    for the Windows environment when these mature.
  
    struct CodaCred {
        vuid_t cr_uid, cr_euid, cr_suid, cr_fsuid; /* Real, effective, set, fs uid*/
        vgid_t cr_gid, cr_egid, cr_sgid, cr_fsgid; /* same for groups */
        vgid_t cr_groups[NGROUPS];        /* Group membership for caller */
    };
  
  
  
    NNOOTTEE It is questionable if we need CodaCreds in Venus. Finally Venus
    doesn't know about groups, although it does create files with the
    default uid/gid.  Perhaps the list of group membership is superfluous.
  
  
    The next item is the fundamental identifier used to identify Coda
    files, the ViceFid.  A fid of a file uniquely defines a file or
    directory in the Coda filesystem within a _c_e_l_l.   (-- A _c_e_l_l is a
    group of Coda servers acting under the aegis of a single system
    control machine or SCM. See the Coda Administration manual for a
    detailed description of the role of the SCM.--)
  
  
    typedef struct ViceFid {
        VolumeId Volume;
        VnodeId Vnode;
        Unique_t Unique;
    } ViceFid;
  
  
  
    Each of the constituent fields: VolumeId, VnodeId and Unique_t are
    unsigned 32 bit integers.  We envisage that a further field will need
    to be prefixed to identify the Coda cell; this will probably take the
    form of a Ipv6 size IP address naming the Coda cell through DNS.
  
    The next important structure shared between Venus and the kernel is
    the attributes of the file.  The following structure is used to
    exchange information.  It has room for future extensions such as
    support for device files (currently not present in Coda).
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    struct coda_vattr {
            enum coda_vtype va_type;        /* vnode type (for create) */
            u_short         va_mode;        /* files access mode and type */
            short           va_nlink;       /* number of references to file */
            vuid_t          va_uid;         /* owner user id */
            vgid_t          va_gid;         /* owner group id */
            long            va_fsid;        /* file system id (dev for now) */
            long            va_fileid;      /* file id */
            u_quad_t        va_size;        /* file size in bytes */
            long            va_blocksize;   /* blocksize preferred for i/o */
            struct timespec va_atime;       /* time of last access */
            struct timespec va_mtime;       /* time of last modification */
            struct timespec va_ctime;       /* time file changed */
            u_long          va_gen;         /* generation number of file */
            u_long          va_flags;       /* flags defined for file */
            dev_t           va_rdev;        /* device special file represents */
            u_quad_t        va_bytes;       /* bytes of disk space held by file */
            u_quad_t        va_filerev;     /* file modification number */
            u_int           va_vaflags;     /* operations flags, see below */
            long            va_spare;       /* remain quad aligned */
    };
  
  
  
  
    44..22..  TThhee ppiiooccttll iinntteerrffaaccee
  
  
    Coda specific requests can be made by application through the pioctl
    interface. The pioctl is implemented as an ordinary ioctl on a
    fictitious file /coda/.CONTROL.  The pioctl call opens this file, gets
    a file handle and makes the ioctl call. Finally it closes the file.
  
    The kernel involvement in this is limited to providing the facility to
    open and close and pass the ioctl message _a_n_d to verify that a path in
    the pioctl data buffers is a file in a Coda filesystem.
  
    The kernel is handed a data packet of the form:
  
        struct {
            const char *path;
            struct ViceIoctl vidata;
            int follow;
        } data;
  
  
  
    where
  
  
    struct ViceIoctl {
            caddr_t in, out;        /* Data to be transferred in, or out */
            short in_size;          /* Size of input buffer <= 2K */
            short out_size;         /* Maximum size of output buffer, <= 2K */
    };
  
  
  
    The path must be a Coda file, otherwise the ioctl upcall will not be
    made.
  
    NNOOTTEE  The data structures and code are a mess.  We need to clean this
    up.
  
    We now proceed to document the individual calls:
  
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    44..33..  rroooott
  
  
    AArrgguummeennttss
  
       iinn empty
  
       oouutt
  
                  struct cfs_root_out {
                      ViceFid VFid;
                  } cfs_root;
  
  
  
    DDeessccrriippttiioonn This call is made to Venus during the initialization of
    the Coda filesystem. If the result is zero, the cfs_root structure
    contains the ViceFid of the root of the Coda filesystem. If a non-zero
    result is generated, its value is a platform dependent error code
    indicating the difficulty Venus encountered in locating the root of
    the Coda filesystem.
  
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    44..44..  llooookkuupp
  
  
    SSuummmmaarryy Find the ViceFid and type of an object in a directory if it
    exists.
  
    AArrgguummeennttss
  
       iinn
  
                  struct  cfs_lookup_in {
                      ViceFid     VFid;
                      char        *name;          /* Place holder for data. */
                  } cfs_lookup;
  
  
  
       oouutt
  
                  struct cfs_lookup_out {
                      ViceFid VFid;
                      int vtype;
                  } cfs_lookup;
  
  
  
    DDeessccrriippttiioonn This call is made to determine the ViceFid and filetype of
    a directory entry.  The directory entry requested carries name name
    and Venus will search the directory identified by cfs_lookup_in.VFid.
    The result may indicate that the name does not exist, or that
    difficulty was encountered in finding it (e.g. due to disconnection).
    If the result is zero, the field cfs_lookup_out.VFid contains the
    targets ViceFid and cfs_lookup_out.vtype the coda_vtype giving the
    type of object the name designates.
  
    The name of the object is an 8 bit character string of maximum length
    CFS_MAXNAMLEN, currently set to 256 (including a 0 terminator.)
  
    It is extremely important to realize that Venus bitwise ors the field
    cfs_lookup.vtype with CFS_NOCACHE to indicate that the object should
    not be put in the kernel name cache.
  
    NNOOTTEE The type of the vtype is currently wrong.  It should be
    coda_vtype. Linux does not take note of CFS_NOCACHE.  It should.
  
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    44..55..  ggeettaattttrr
  
  
    SSuummmmaarryy Get the attributes of a file.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_getattr_in {
                      ViceFid VFid;
                      struct coda_vattr attr; /* XXXXX */
                  } cfs_getattr;
  
  
  
       oouutt
  
                  struct cfs_getattr_out {
                      struct coda_vattr attr;
                  } cfs_getattr;
  
  
  
    DDeessccrriippttiioonn This call returns the attributes of the file identified by
    fid.
  
    EErrrroorrss Errors can occur if the object with fid does not exist, is
    unaccessible or if the caller does not have permission to fetch
    attributes.
  
    NNoottee Many kernel FS drivers (Linux, NT and Windows 95) need to acquire
    the attributes as well as the Fid for the instantiation of an internal
    "inode" or "FileHandle".  A significant improvement in performance on
    such systems could be made by combining the _l_o_o_k_u_p and _g_e_t_a_t_t_r calls
    both at the Venus/kernel interaction level and at the RPC level.
  
    The vattr structure included in the input arguments is superfluous and
    should be removed.
  
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    44..66..  sseettaattttrr
  
  
    SSuummmmaarryy Set the attributes of a file.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_setattr_in {
                      ViceFid VFid;
                      struct coda_vattr attr;
                  } cfs_setattr;
  
  
  
  
       oouutt
          empty
  
    DDeessccrriippttiioonn The structure attr is filled with attributes to be changed
    in BSD style.  Attributes not to be changed are set to -1, apart from
    vtype which is set to VNON. Other are set to the value to be assigned.
    The only attributes which the FS driver may request to change are the
    mode, owner, groupid, atime, mtime and ctime.  The return value
    indicates success or failure.
  
    EErrrroorrss A variety of errors can occur.  The object may not exist, may
    be inaccessible, or permission may not be granted by Venus.
  
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    44..77..  aacccceessss
  
  
    SSuummmmaarryy
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_access_in {
                      ViceFid     VFid;
                      int flags;
                  } cfs_access;
  
  
  
       oouutt
          empty
  
    DDeessccrriippttiioonn Verify if access to the object identified by VFid for
    operations described by flags is permitted.  The result indicates if
    access will be granted.  It is important to remember that Coda uses
    ACLs to enforce protection and that ultimately the servers, not the
    clients enforce the security of the system.  The result of this call
    will depend on whether a _t_o_k_e_n is held by the user.
  
    EErrrroorrss The object may not exist, or the ACL describing the protection
    may not be accessible.
  
    0wpage
  
    44..88..  ccrreeaattee
  
  
    SSuummmmaarryy Invoked to create a file
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_create_in {
                      ViceFid VFid;
                      struct coda_vattr attr;
                      int excl;
                      int mode;
                      char        *name;          /* Place holder for data. */
                  } cfs_create;
  
  
  
  
       oouutt
  
                  struct cfs_create_out {
                      ViceFid VFid;
                      struct coda_vattr attr;
                  } cfs_create;
  
  
  
    DDeessccrriippttiioonn  This upcall is invoked to request creation of a file.
    The file will be created in the directory identified by VFid, its name
    will be name, and the mode will be mode.  If excl is set an error will
    be returned if the file already exists.  If the size field in attr is
    set to zero the file will be truncated.  The uid and gid of the file
    are set by converting the CodaCred to a uid using a macro CRTOUID
    (this macro is platform dependent).  Upon success the VFid and
    attributes of the file are returned.  The Coda FS Driver will normally
    instantiate a vnode, inode or file handle at kernel level for the new
    object.
  
  
    EErrrroorrss A variety of errors can occur. Permissions may be insufficient.
    If the object exists and is not a file the error EISDIR is returned
    under Unix.
  
    NNOOTTEE The packing of parameters is very inefficient and appears to
    indicate confusion between the system call creat and the VFS operation
    create. The VFS operation create is only called to create new objects.
    This create call differs from the Unix one in that it is not invoked
    to return a file descriptor. The truncate and exclusive options,
    together with the mode, could simply be part of the mode as it is
    under Unix.  There should be no flags argument; this is used in open
    (2) to return a file descriptor for READ or WRITE mode.
  
    The attributes of the directory should be returned too, since the size
    and mtime changed.
  
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    44..99..  mmkkddiirr
  
  
    SSuummmmaarryy Create a new directory.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_mkdir_in {
                      ViceFid     VFid;
                      struct coda_vattr attr;
                      char        *name;          /* Place holder for data. */
                  } cfs_mkdir;
  
  
  
       oouutt
  
                  struct cfs_mkdir_out {
                      ViceFid VFid;
                      struct coda_vattr attr;
                  } cfs_mkdir;
  
  
  
  
    DDeessccrriippttiioonn This call is similar to create but creates a directory.
    Only the mode field in the input parameters is used for creation.
    Upon successful creation, the attr returned contains the attributes of
    the new directory.
  
    EErrrroorrss As for create.
  
    NNOOTTEE The input parameter should be changed to mode instead of
    attributes.
  
    The attributes of the parent should be returned since the size and
    mtime changes.
  
    0wpage
  
    44..1100..  lliinnkk
  
  
    SSuummmmaarryy Create a link to an existing file.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_link_in {
                      ViceFid sourceFid;          /* cnode to link *to* */
                      ViceFid destFid;            /* Directory in which to place link */
                      char        *tname;         /* Place holder for data. */
                  } cfs_link;
  
  
  
       oouutt
          empty
  
    DDeessccrriippttiioonn This call creates a link to the sourceFid in the directory
    identified by destFid with name tname.  The source must reside in the
    target's parent, i.e. the source must be have parent destFid, i.e. Coda
    does not support cross directory hard links.  Only the return value is
    relevant.  It indicates success or the type of failure.
  
    EErrrroorrss The usual errors can occur.0wpage
  
    44..1111..  ssyymmlliinnkk
  
  
    SSuummmmaarryy create a symbolic link
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_symlink_in {
                      ViceFid     VFid;          /* Directory to put symlink in */
                      char        *srcname;
                      struct coda_vattr attr;
                      char        *tname;
                  } cfs_symlink;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn Create a symbolic link. The link is to be placed in the
    directory identified by VFid and named tname.  It should point to the
    pathname srcname.  The attributes of the newly created object are to
    be set to attr.
  
    EErrrroorrss
  
    NNOOTTEE The attributes of the target directory should be returned since
    its size changed.
  
    0wpage
  
    44..1122..  rreemmoovvee
  
  
    SSuummmmaarryy Remove a file
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_remove_in {
                      ViceFid     VFid;
                      char        *name;          /* Place holder for data. */
                  } cfs_remove;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn  Remove file named cfs_remove_in.name in directory
    identified by   VFid.
  
    EErrrroorrss
  
    NNOOTTEE The attributes of the directory should be returned since its
    mtime and size may change.
  
    0wpage
  
    44..1133..  rrmmddiirr
  
  
    SSuummmmaarryy Remove a directory
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_rmdir_in {
                      ViceFid     VFid;
                      char        *name;          /* Place holder for data. */
                  } cfs_rmdir;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn Remove the directory with name name from the directory
    identified by VFid.
  
    EErrrroorrss
  
    NNOOTTEE The attributes of the parent directory should be returned since
    its mtime and size may change.
  
    0wpage
  
    44..1144..  rreeaaddlliinnkk
  
  
    SSuummmmaarryy Read the value of a symbolic link.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_readlink_in {
                      ViceFid VFid;
                  } cfs_readlink;
  
  
  
       oouutt
  
                  struct cfs_readlink_out {
                      int count;
                      caddr_t     data;           /* Place holder for data. */
                  } cfs_readlink;
  
  
  
    DDeessccrriippttiioonn This routine reads the contents of symbolic link
    identified by VFid into the buffer data.  The buffer data must be able
    to hold any name up to CFS_MAXNAMLEN (PATH or NAM??).
  
    EErrrroorrss No unusual errors.
  
    0wpage
  
    44..1155..  ooppeenn
  
  
    SSuummmmaarryy Open a file.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_open_in {
                      ViceFid     VFid;
                      int flags;
                  } cfs_open;
  
  
  
       oouutt
  
                  struct cfs_open_out {
                      dev_t       dev;
                      ino_t       inode;
                  } cfs_open;
  
  
  
    DDeessccrriippttiioonn  This request asks Venus to place the file identified by
    VFid in its cache and to note that the calling process wishes to open
    it with flags as in open(2).  The return value to the kernel differs
    for Unix and Windows systems.  For Unix systems the Coda FS Driver is
    informed of the device and inode number of the container file in the
    fields dev and inode.  For Windows the path of the container file is
    returned to the kernel.
    EErrrroorrss
  
    NNOOTTEE Currently the cfs_open_out structure is not properly adapted to
    deal with the Windows case.  It might be best to implement two
    upcalls, one to open aiming at a container file name, the other at a
    container file inode.
  
    0wpage
  
    44..1166..  cclloossee
  
  
    SSuummmmaarryy Close a file, update it on the servers.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_close_in {
                      ViceFid     VFid;
                      int flags;
                  } cfs_close;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn Close the file identified by VFid.
  
    EErrrroorrss
  
    NNOOTTEE The flags argument is bogus and not used.  However, Venus' code
    has room to deal with an execp input field, probably this field should
    be used to inform Venus that the file was closed but is still memory
    mapped for execution.  There are comments about fetching versus not
    fetching the data in Venus vproc_vfscalls.  This seems silly.  If a
    file is being closed, the data in the container file is to be the new
    data.  Here again the execp flag might be in play to create confusion:
    currently Venus might think a file can be flushed from the cache when
    it is still memory mapped.  This needs to be understood.
  
    0wpage
  
    44..1177..  iiooccttll
  
  
    SSuummmmaarryy Do an ioctl on a file. This includes the pioctl interface.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_ioctl_in {
                      ViceFid VFid;
                      int cmd;
                      int len;
                      int rwflag;
                      char *data;                 /* Place holder for data. */
                  } cfs_ioctl;
  
  
  
       oouutt
  
  
                  struct cfs_ioctl_out {
                      int len;
                      caddr_t     data;           /* Place holder for data. */
                  } cfs_ioctl;
  
  
  
    DDeessccrriippttiioonn Do an ioctl operation on a file.  The command, len and
    data arguments are filled as usual.  flags is not used by Venus.
  
    EErrrroorrss
  
    NNOOTTEE Another bogus parameter.  flags is not used.  What is the
    business about PREFETCHING in the Venus code?
  
  
    0wpage
  
    44..1188..  rreennaammee
  
  
    SSuummmmaarryy Rename a fid.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_rename_in {
                      ViceFid     sourceFid;
                      char        *srcname;
                      ViceFid destFid;
                      char        *destname;
                  } cfs_rename;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn  Rename the object with name srcname in directory
    sourceFid to destname in destFid.   It is important that the names
    srcname and destname are 0 terminated strings.  Strings in Unix
    kernels are not always null terminated.
  
    EErrrroorrss
  
    0wpage
  
    44..1199..  rreeaaddddiirr
  
  
    SSuummmmaarryy Read directory entries.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_readdir_in {
                      ViceFid     VFid;
                      int count;
                      int offset;
                  } cfs_readdir;
  
  
  
  
       oouutt
  
                  struct cfs_readdir_out {
                      int size;
                      caddr_t     data;           /* Place holder for data. */
                  } cfs_readdir;
  
  
  
    DDeessccrriippttiioonn Read directory entries from VFid starting at offset and
    read at most count bytes.  Returns the data in data and returns
    the size in size.
  
    EErrrroorrss
  
    NNOOTTEE This call is not used.  Readdir operations exploit container
    files.  We will re-evaluate this during the directory revamp which is
    about to take place.
  
    0wpage
  
    44..2200..  vvggeett
  
  
    SSuummmmaarryy instructs Venus to do an FSDB->Get.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_vget_in {
                      ViceFid VFid;
                  } cfs_vget;
  
  
  
       oouutt
  
                  struct cfs_vget_out {
                      ViceFid VFid;
                      int vtype;
                  } cfs_vget;
  
  
  
    DDeessccrriippttiioonn This upcall asks Venus to do a get operation on an fsobj
    labelled by VFid.
  
    EErrrroorrss
  
    NNOOTTEE This operation is not used.  However, it is extremely useful
    since it can be used to deal with read/write memory mapped files.
    These can be "pinned" in the Venus cache using vget and released with
    inactive.
  
    0wpage
  
    44..2211..  ffssyynncc
  
  
    SSuummmmaarryy Tell Venus to update the RVM attributes of a file.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_fsync_in {
                      ViceFid VFid;
                  } cfs_fsync;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn Ask Venus to update RVM attributes of object VFid. This
    should be called as part of kernel level fsync type calls.  The
    result indicates if the syncing was successful.
  
    EErrrroorrss
  
    NNOOTTEE Linux does not implement this call. It should.
  
    0wpage
  
    44..2222..  iinnaaccttiivvee
  
  
    SSuummmmaarryy Tell Venus a vnode is no longer in use.
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_inactive_in {
                      ViceFid VFid;
                  } cfs_inactive;
  
  
  
       oouutt
          none
  
    DDeessccrriippttiioonn This operation returns EOPNOTSUPP.
  
    EErrrroorrss
  
    NNOOTTEE This should perhaps be removed.
  
    0wpage
  
    44..2233..  rrddwwrr
  
  
    SSuummmmaarryy Read or write from a file
  
    AArrgguummeennttss
  
       iinn
  
                  struct cfs_rdwr_in {
                      ViceFid     VFid;
                      int rwflag;
                      int count;
                      int offset;
                      int ioflag;
                      caddr_t     data;           /* Place holder for data. */
                  } cfs_rdwr;
  
  
  
  
       oouutt
  
                  struct cfs_rdwr_out {
                      int rwflag;
                      int count;
                      caddr_t     data;   /* Place holder for data. */
                  } cfs_rdwr;
  
  
  
    DDeessccrriippttiioonn This upcall asks Venus to read or write from a file.
  
    EErrrroorrss
  
    NNOOTTEE It should be removed since it is against the Coda philosophy that
    read/write operations never reach Venus.  I have been told the
    operation does not work.  It is not currently used.
  
  
    0wpage
  
    44..2244..  ooddyymmoouunntt
  
  
    SSuummmmaarryy Allows mounting multiple Coda "filesystems" on one Unix mount
    point.
  
    AArrgguummeennttss
  
       iinn
  
                  struct ody_mount_in {
                      char        *name;          /* Place holder for data. */
                  } ody_mount;
  
  
  
       oouutt
  
                  struct ody_mount_out {
                      ViceFid VFid;
                  } ody_mount;
  
  
  
    DDeessccrriippttiioonn  Asks Venus to return the rootfid of a Coda system named
    name.  The fid is returned in VFid.
  
    EErrrroorrss
  
    NNOOTTEE This call was used by David for dynamic sets.  It should be
    removed since it causes a jungle of pointers in the VFS mounting area.
    It is not used by Coda proper.  Call is not implemented by Venus.
  
    0wpage
  
    44..2255..  ooddyy__llooookkuupp
  
  
    SSuummmmaarryy Looks up something.
  
    AArrgguummeennttss
  
       iinn irrelevant
  
  
       oouutt
          irrelevant
  
    DDeessccrriippttiioonn
  
    EErrrroorrss
  
    NNOOTTEE Gut it. Call is not implemented by Venus.
  
    0wpage
  
    44..2266..  ooddyy__eexxppaanndd
  
  
    SSuummmmaarryy expands something in a dynamic set.
  
    AArrgguummeennttss
  
       iinn irrelevant
  
       oouutt
          irrelevant
  
    DDeessccrriippttiioonn
  
    EErrrroorrss
  
    NNOOTTEE Gut it.  Call is not implemented by Venus.
  
    0wpage
  
    44..2277..  pprreeffeettcchh
  
  
    SSuummmmaarryy Prefetch a dynamic set.
  
    AArrgguummeennttss
  
       iinn Not documented.
  
       oouutt
          Not documented.
  
    DDeessccrriippttiioonn  Venus worker.cc has support for this call, although it is
    noted that it doesn't work.  Not surprising, since the kernel does not
    have support for it. (ODY_PREFETCH is not a defined operation).
  
    EErrrroorrss
  
    NNOOTTEE Gut it. It isn't working and isn't used by Coda.
  
  
    0wpage
  
    44..2288..  ssiiggnnaall
  
  
    SSuummmmaarryy Send Venus a signal about an upcall.
  
    AArrgguummeennttss
  
       iinn none
  
       oouutt
          not applicable.
  
    DDeessccrriippttiioonn  This is an out-of-band upcall to Venus to inform Venus
    that the calling process received a signal after Venus read the
    message from the input queue.  Venus is supposed to clean up the
    operation.
  
    EErrrroorrss No reply is given.
  
    NNOOTTEE We need to better understand what Venus needs to clean up and if
    it is doing this correctly.  Also we need to handle multiple upcall
    per system call situations correctly.  It would be important to know
    what state changes in Venus take place after an upcall for which the
    kernel is responsible for notifying Venus to clean up (e.g. open
    definitely is such a state change, but many others are maybe not).
  
    0wpage
  
    55..  TThhee mmiinniiccaacchhee aanndd ddoowwnnccaallllss
  
  
    The Coda FS Driver can cache results of lookup and access upcalls, to
    limit the frequency of upcalls.  Upcalls carry a price since a process
    context switch needs to take place.  The counterpart of caching the
    information is that Venus will notify the FS Driver that cached
    entries must be flushed or renamed.
  
    The kernel code generally has to maintain a structure which links the
    internal file handles (called vnodes in BSD, inodes in Linux and
    FileHandles in Windows) with the ViceFid's which Venus maintains.  The
    reason is that frequent translations back and forth are needed in
    order to make upcalls and use the results of upcalls.  Such linking
    objects are called ccnnooddeess.
  
    The current minicache implementations have cache entries which record
    the following:
  
    1. the name of the file
  
    2. the cnode of the directory containing the object
  
    3. a list of CodaCred's for which the lookup is permitted.
  
    4. the cnode of the object
  
    The lookup call in the Coda FS Driver may request the cnode of the
    desired object from the cache, by passing its name, directory and the
    CodaCred's of the caller.  The cache will return the cnode or indicate
    that it cannot be found.  The Coda FS Driver must be careful to
    invalidate cache entries when it modifies or removes objects.
  
    When Venus obtains information that indicates that cache entries are
    no longer valid, it will make a downcall to the kernel.  Downcalls are
    intercepted by the Coda FS Driver and lead to cache invalidations of
    the kind described below.  The Coda FS Driver does not return an error
    unless the downcall data could not be read into kernel memory.
  
  
    55..11..  IINNVVAALLIIDDAATTEE
  
  
    No information is available on this call.
  
  
    55..22..  FFLLUUSSHH
  
  
  
    AArrgguummeennttss None
  
    SSuummmmaarryy Flush the name cache entirely.
  
    DDeessccrriippttiioonn Venus issues this call upon startup and when it dies. This
    is to prevent stale cache information being held.  Some operating
    systems allow the kernel name cache to be switched off dynamically.
    When this is done, this downcall is made.
  
  
    55..33..  PPUURRGGEEUUSSEERR
  
  
    AArrgguummeennttss
  
            struct cfs_purgeuser_out {/* CFS_PURGEUSER is a venus->kernel call */
                struct CodaCred cred;
            } cfs_purgeuser;
  
  
  
    DDeessccrriippttiioonn Remove all entries in the cache carrying the Cred.  This
    call is issued when tokens for a user expire or are flushed.
  
  
    55..44..  ZZAAPPFFIILLEE
  
  
    AArrgguummeennttss
  
            struct cfs_zapfile_out {  /* CFS_ZAPFILE is a venus->kernel call */
                ViceFid CodaFid;
            } cfs_zapfile;
  
  
  
    DDeessccrriippttiioonn Remove all entries which have the (dir vnode, name) pair.
    This is issued as a result of an invalidation of cached attributes of
    a vnode.
  
    NNOOTTEE Call is not named correctly in NetBSD and Mach.  The minicache
    zapfile routine takes different arguments. Linux does not implement
    the invalidation of attributes correctly.
  
  
  
    55..55..  ZZAAPPDDIIRR
  
  
    AArrgguummeennttss
  
            struct cfs_zapdir_out {   /* CFS_ZAPDIR is a venus->kernel call */
                ViceFid CodaFid;
            } cfs_zapdir;
  
  
  
    DDeessccrriippttiioonn Remove all entries in the cache lying in a directory
    CodaFid, and all children of this directory. This call is issued when
    Venus receives a callback on the directory.
  
  
    55..66..  ZZAAPPVVNNOODDEE
  
  
  
    AArrgguummeennttss
  
            struct cfs_zapvnode_out { /* CFS_ZAPVNODE is a venus->kernel call */
                struct CodaCred cred;
                ViceFid VFid;
            } cfs_zapvnode;
  
  
  
    DDeessccrriippttiioonn Remove all entries in the cache carrying the cred and VFid
    as in the arguments. This downcall is probably never issued.
  
  
    55..77..  PPUURRGGEEFFIIDD
  
  
    SSuummmmaarryy
  
    AArrgguummeennttss
  
            struct cfs_purgefid_out { /* CFS_PURGEFID is a venus->kernel call */
                ViceFid CodaFid;
            } cfs_purgefid;
  
  
  
    DDeessccrriippttiioonn Flush the attribute for the file. If it is a dir (odd
    vnode), purge its children from the namecache and remove the file from the
    namecache.
  
  
  
    55..88..  RREEPPLLAACCEE
  
  
    SSuummmmaarryy Replace the Fid's for a collection of names.
  
    AArrgguummeennttss
  
            struct cfs_replace_out { /* cfs_replace is a venus->kernel call */
                ViceFid NewFid;
                ViceFid OldFid;
            } cfs_replace;
  
  
  
    DDeessccrriippttiioonn This routine replaces a ViceFid in the name cache with
    another.  It is added to allow Venus during reintegration to replace
    locally allocated temp fids while disconnected with global fids even
    when the reference counts on those fids are not zero.
  
    0wpage
  
    66..  IInniittiiaalliizzaattiioonn aanndd cclleeaannuupp
  
  
    This section gives brief hints as to desirable features for the Coda
    FS Driver at startup and upon shutdown or Venus failures.  Before
    entering the discussion it is useful to repeat that the Coda FS Driver
    maintains the following data:
  
  
    1. message queues
  
    2. cnodes
  
    3. name cache entries
  
       The name cache entries are entirely private to the driver, so they
       can easily be manipulated.   The message queues will generally have
       clear points of initialization and destruction.  The cnodes are
       much more delicate.  User processes hold reference counts in Coda
       filesystems and it can be difficult to clean up the cnodes.
  
    It can expect requests through:
  
    1. the message subsystem
  
    2. the VFS layer
  
    3. pioctl interface
  
       Currently the _p_i_o_c_t_l passes through the VFS for Coda so we can
       treat these similarly.
  
  
    66..11..  RReeqquuiirreemmeennttss
  
  
    The following requirements should be accommodated:
  
    1. The message queues should have open and close routines.  On Unix
       the opening of the character devices are such routines.
  
    +o  Before opening, no messages can be placed.
  
    +o  Opening will remove any old messages still pending.
  
    +o  Close will notify any sleeping processes that their upcall cannot
       be completed.
  
    +o  Close will free all memory allocated by the message queues.
  
  
    2. At open the namecache shall be initialized to empty state.
  
    3. Before the message queues are open, all VFS operations will fail.
       Fortunately this can be achieved by making sure than mounting the
       Coda filesystem cannot succeed before opening.
  
    4. After closing of the queues, no VFS operations can succeed.  Here
       one needs to be careful, since a few operations (lookup,
       read/write, readdir) can proceed without upcalls.  These must be
       explicitly blocked.
  
    5. Upon closing the namecache shall be flushed and disabled.
  
    6. All memory held by cnodes can be freed without relying on upcalls.
  
    7. Unmounting the file system can be done without relying on upcalls.
  
    8. Mounting the Coda filesystem should fail gracefully if Venus cannot
       get the rootfid or the attributes of the rootfid.  The latter is
       best implemented by Venus fetching these objects before attempting
       to mount.
  
    NNOOTTEE  NetBSD in particular but also Linux have not implemented the
    above requirements fully.  For smooth operation this needs to be
    corrected.