linux/Documentation/filesystems/coda.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3===========================
   4Coda Kernel-Venus Interface
   5===========================
   6
   7.. Note::
   8
   9   This is one of the technical documents describing a component of
  10   Coda -- this document describes the client kernel-Venus interface.
  11
  12For more information:
  13
  14  http://www.coda.cs.cmu.edu
  15
  16For user level software needed to run Coda:
  17
  18  ftp://ftp.coda.cs.cmu.edu
  19
  20To run Coda you need to get a user level cache manager for the client,
  21named Venus, as well as tools to manipulate ACLs, to log in, etc.  The
  22client needs to have the Coda filesystem selected in the kernel
  23configuration.
  24
  25The server needs a user level server and at present does not depend on
  26kernel support.
  27
  28  The Venus kernel interface
  29
  30  Peter J. Braam
  31
  32  v1.0, Nov 9, 1997
  33
  34  This document describes the communication between Venus and kernel
  35  level filesystem code needed for the operation of the Coda file sys-
  36  tem.  This document version is meant to describe the current interface
  37  (version 1.0) as well as improvements we envisage.
  38
  39.. Table of Contents
  40
  41  1. Introduction
  42
  43  2. Servicing Coda filesystem calls
  44
  45  3. The message layer
  46
  47     3.1 Implementation details
  48
  49  4. The interface at the call level
  50
  51     4.1 Data structures shared by the kernel and Venus
  52     4.2 The pioctl interface
  53     4.3 root
  54     4.4 lookup
  55     4.5 getattr
  56     4.6 setattr
  57     4.7 access
  58     4.8 create
  59     4.9 mkdir
  60     4.10 link
  61     4.11 symlink
  62     4.12 remove
  63     4.13 rmdir
  64     4.14 readlink
  65     4.15 open
  66     4.16 close
  67     4.17 ioctl
  68     4.18 rename
  69     4.19 readdir
  70     4.20 vget
  71     4.21 fsync
  72     4.22 inactive
  73     4.23 rdwr
  74     4.24 odymount
  75     4.25 ody_lookup
  76     4.26 ody_expand
  77     4.27 prefetch
  78     4.28 signal
  79
  80  5. The minicache and downcalls
  81
  82     5.1 INVALIDATE
  83     5.2 FLUSH
  84     5.3 PURGEUSER
  85     5.4 ZAPFILE
  86     5.5 ZAPDIR
  87     5.6 ZAPVNODE
  88     5.7 PURGEFID
  89     5.8 REPLACE
  90
  91  6. Initialization and cleanup
  92
  93     6.1 Requirements
  94
  951. Introduction
  96===============
  97
  98  A key component in the Coda Distributed File System is the cache
  99  manager, Venus.
 100
 101  When processes on a Coda enabled system access files in the Coda
 102  filesystem, requests are directed at the filesystem layer in the
 103  operating system. The operating system will communicate with Venus to
 104  service the request for the process.  Venus manages a persistent
 105  client cache and makes remote procedure calls to Coda file servers and
 106  related servers (such as authentication servers) to service these
 107  requests it receives from the operating system.  When Venus has
 108  serviced a request it replies to the operating system with appropriate
 109  return codes, and other data related to the request.  Optionally the
 110  kernel support for Coda may maintain a minicache of recently processed
 111  requests to limit the number of interactions with Venus.  Venus
 112  possesses the facility to inform the kernel when elements from its
 113  minicache are no longer valid.
 114
 115  This document describes precisely this communication between the
 116  kernel and Venus.  The definitions of so called upcalls and downcalls
 117  will be given with the format of the data they handle. We shall also
 118  describe the semantic invariants resulting from the calls.
 119
 120  Historically Coda was implemented in a BSD file system in Mach 2.6.
 121  The interface between the kernel and Venus is very similar to the BSD
 122  VFS interface.  Similar functionality is provided, and the format of
 123  the parameters and returned data is very similar to the BSD VFS.  This
 124  leads to an almost natural environment for implementing a kernel-level
 125  filesystem driver for Coda in a BSD system.  However, other operating
 126  systems such as Linux and Windows 95 and NT have virtual filesystem
 127  with different interfaces.
 128
 129  To implement Coda on these systems some reverse engineering of the
 130  Venus/Kernel protocol is necessary.  Also it came to light that other
 131  systems could profit significantly from certain small optimizations
 132  and modifications to the protocol. To facilitate this work as well as
 133  to make future ports easier, communication between Venus and the
 134  kernel should be documented in great detail.  This is the aim of this
 135  document.
 136
 1372.  Servicing Coda filesystem calls
 138===================================
 139
 140  The service of a request for a Coda file system service originates in
 141  a process P which accessing a Coda file. It makes a system call which
 142  traps to the OS kernel. Examples of such calls trapping to the kernel
 143  are ``read``, ``write``, ``open``, ``close``, ``create``, ``mkdir``,
 144  ``rmdir``, ``chmod`` in a Unix ontext.  Similar calls exist in the Win32
 145  environment, and are named ``CreateFile``.
 146
 147  Generally the operating system handles the request in a virtual
 148  filesystem (VFS) layer, which is named I/O Manager in NT and IFS
 149  manager in Windows 95.  The VFS is responsible for partial processing
 150  of the request and for locating the specific filesystem(s) which will
 151  service parts of the request.  Usually the information in the path
 152  assists in locating the correct FS drivers.  Sometimes after extensive
 153  pre-processing, the VFS starts invoking exported routines in the FS
 154  driver.  This is the point where the FS specific processing of the
 155  request starts, and here the Coda specific kernel code comes into
 156  play.
 157
 158  The FS layer for Coda must expose and implement several interfaces.
 159  First and foremost the VFS must be able to make all necessary calls to
 160  the Coda FS layer, so the Coda FS driver must expose the VFS interface
 161  as applicable in the operating system. These differ very significantly
 162  among operating systems, but share features such as facilities to
 163  read/write and create and remove objects.  The Coda FS layer services
 164  such VFS requests by invoking one or more well defined services
 165  offered by the cache manager Venus.  When the replies from Venus have
 166  come back to the FS driver, servicing of the VFS call continues and
 167  finishes with a reply to the kernel's VFS. Finally the VFS layer
 168  returns to the process.
 169
 170  As a result of this design a basic interface exposed by the FS driver
 171  must allow Venus to manage message traffic.  In particular Venus must
 172  be able to retrieve and place messages and to be notified of the
 173  arrival of a new message. The notification must be through a mechanism
 174  which does not block Venus since Venus must attend to other tasks even
 175  when no messages are waiting or being processed.
 176
 177  **Interfaces of the Coda FS Driver**
 178
 179  Furthermore the FS layer provides for a special path of communication
 180  between a user process and Venus, called the pioctl interface. The
 181  pioctl interface is used for Coda specific services, such as
 182  requesting detailed information about the persistent cache managed by
 183  Venus. Here the involvement of the kernel is minimal.  It identifies
 184  the calling process and passes the information on to Venus.  When
 185  Venus replies the response is passed back to the caller in unmodified
 186  form.
 187
 188  Finally Venus allows the kernel FS driver to cache the results from
 189  certain services.  This is done to avoid excessive context switches
 190  and results in an efficient system.  However, Venus may acquire
 191  information, for example from the network which implies that cached
 192  information must be flushed or replaced. Venus then makes a downcall
 193  to the Coda FS layer to request flushes or updates in the cache.  The
 194  kernel FS driver handles such requests synchronously.
 195
 196  Among these interfaces the VFS interface and the facility to place,
 197  receive and be notified of messages are platform specific.  We will
 198  not go into the calls exported to the VFS layer but we will state the
 199  requirements of the message exchange mechanism.
 200
 201
 2023.  The message layer
 203=====================
 204
 205  At the lowest level the communication between Venus and the FS driver
 206  proceeds through messages.  The synchronization between processes
 207  requesting Coda file service and Venus relies on blocking and waking
 208  up processes.  The Coda FS driver processes VFS- and pioctl-requests
 209  on behalf of a process P, creates messages for Venus, awaits replies
 210  and finally returns to the caller.  The implementation of the exchange
 211  of messages is platform specific, but the semantics have (so far)
 212  appeared to be generally applicable.  Data buffers are created by the
 213  FS Driver in kernel memory on behalf of P and copied to user memory in
 214  Venus.
 215
 216  The FS Driver while servicing P makes upcalls to Venus.  Such an
 217  upcall is dispatched to Venus by creating a message structure.  The
 218  structure contains the identification of P, the message sequence
 219  number, the size of the request and a pointer to the data in kernel
 220  memory for the request.  Since the data buffer is re-used to hold the
 221  reply from Venus, there is a field for the size of the reply.  A flags
 222  field is used in the message to precisely record the status of the
 223  message.  Additional platform dependent structures involve pointers to
 224  determine the position of the message on queues and pointers to
 225  synchronization objects.  In the upcall routine the message structure
 226  is filled in, flags are set to 0, and it is placed on the *pending*
 227  queue.  The routine calling upcall is responsible for allocating the
 228  data buffer; its structure will be described in the next section.
 229
 230  A facility must exist to notify Venus that the message has been
 231  created, and implemented using available synchronization objects in
 232  the OS. This notification is done in the upcall context of the process
 233  P. When the message is on the pending queue, process P cannot proceed
 234  in upcall.  The (kernel mode) processing of P in the filesystem
 235  request routine must be suspended until Venus has replied.  Therefore
 236  the calling thread in P is blocked in upcall.  A pointer in the
 237  message structure will locate the synchronization object on which P is
 238  sleeping.
 239
 240  Venus detects the notification that a message has arrived, and the FS
 241  driver allow Venus to retrieve the message with a getmsg_from_kernel
 242  call. This action finishes in the kernel by putting the message on the
 243  queue of processing messages and setting flags to READ.  Venus is
 244  passed the contents of the data buffer. The getmsg_from_kernel call
 245  now returns and Venus processes the request.
 246
 247  At some later point the FS driver receives a message from Venus,
 248  namely when Venus calls sendmsg_to_kernel.  At this moment the Coda FS
 249  driver looks at the contents of the message and decides if:
 250
 251
 252  *  the message is a reply for a suspended thread P.  If so it removes
 253     the message from the processing queue and marks the message as
 254     WRITTEN.  Finally, the FS driver unblocks P (still in the kernel
 255     mode context of Venus) and the sendmsg_to_kernel call returns to
 256     Venus.  The process P will be scheduled at some point and continues
 257     processing its upcall with the data buffer replaced with the reply
 258     from Venus.
 259
 260  *  The message is a ``downcall``.  A downcall is a request from Venus to
 261     the FS Driver. The FS driver processes the request immediately
 262     (usually a cache eviction or replacement) and when it finishes
 263     sendmsg_to_kernel returns.
 264
 265  Now P awakes and continues processing upcall.  There are some
 266  subtleties to take account of. First P will determine if it was woken
 267  up in upcall by a signal from some other source (for example an
 268  attempt to terminate P) or as is normally the case by Venus in its
 269  sendmsg_to_kernel call.  In the normal case, the upcall routine will
 270  deallocate the message structure and return.  The FS routine can proceed
 271  with its processing.
 272
 273
 274  **Sleeping and IPC arrangements**
 275
 276  In case P is woken up by a signal and not by Venus, it will first look
 277  at the flags field.  If the message is not yet READ, the process P can
 278  handle its signal without notifying Venus.  If Venus has READ, and
 279  the request should not be processed, P can send Venus a signal message
 280  to indicate that it should disregard the previous message.  Such
 281  signals are put in the queue at the head, and read first by Venus.  If
 282  the message is already marked as WRITTEN it is too late to stop the
 283  processing.  The VFS routine will now continue.  (-- If a VFS request
 284  involves more than one upcall, this can lead to complicated state, an
 285  extra field "handle_signals" could be added in the message structure
 286  to indicate points of no return have been passed.--)
 287
 288
 289
 2903.1.  Implementation details
 291----------------------------
 292
 293  The Unix implementation of this mechanism has been through the
 294  implementation of a character device associated with Coda.  Venus
 295  retrieves messages by doing a read on the device, replies are sent
 296  with a write and notification is through the select system call on the
 297  file descriptor for the device.  The process P is kept waiting on an
 298  interruptible wait queue object.
 299
 300  In Windows NT and the DPMI Windows 95 implementation a DeviceIoControl
 301  call is used.  The DeviceIoControl call is designed to copy buffers
 302  from user memory to kernel memory with OPCODES. The sendmsg_to_kernel
 303  is issued as a synchronous call, while the getmsg_from_kernel call is
 304  asynchronous.  Windows EventObjects are used for notification of
 305  message arrival.  The process P is kept waiting on a KernelEvent
 306  object in NT and a semaphore in Windows 95.
 307
 308
 3094.  The interface at the call level
 310===================================
 311
 312
 313  This section describes the upcalls a Coda FS driver can make to Venus.
 314  Each of these upcalls make use of two structures: inputArgs and
 315  outputArgs.   In pseudo BNF form the structures take the following
 316  form::
 317
 318
 319        struct inputArgs {
 320            u_long opcode;
 321            u_long unique;     /* Keep multiple outstanding msgs distinct */
 322            u_short pid;                 /* Common to all */
 323            u_short pgid;                /* Common to all */
 324            struct CodaCred cred;        /* Common to all */
 325
 326            <union "in" of call dependent parts of inputArgs>
 327        };
 328
 329        struct outputArgs {
 330            u_long opcode;
 331            u_long unique;       /* Keep multiple outstanding msgs distinct */
 332            u_long result;
 333
 334            <union "out" of call dependent parts of inputArgs>
 335        };
 336
 337
 338
 339  Before going on let us elucidate the role of the various fields. The
 340  inputArgs start with the opcode which defines the type of service
 341  requested from Venus. There are approximately 30 upcalls at present
 342  which we will discuss.   The unique field labels the inputArg with a
 343  unique number which will identify the message uniquely.  A process and
 344  process group id are passed.  Finally the credentials of the caller
 345  are included.
 346
 347  Before delving into the specific calls we need to discuss a variety of
 348  data structures shared by the kernel and Venus.
 349
 350
 351
 352
 3534.1.  Data structures shared by the kernel and Venus
 354----------------------------------------------------
 355
 356
 357  The CodaCred structure defines a variety of user and group ids as
 358  they are set for the calling process. The vuid_t and vgid_t are 32 bit
 359  unsigned integers.  It also defines group membership in an array.  On
 360  Unix the CodaCred has proven sufficient to implement good security
 361  semantics for Coda but the structure may have to undergo modification
 362  for the Windows environment when these mature::
 363
 364        struct CodaCred {
 365            vuid_t cr_uid, cr_euid, cr_suid, cr_fsuid; /* Real, effective, set, fs uid */
 366            vgid_t cr_gid, cr_egid, cr_sgid, cr_fsgid; /* same for groups */
 367            vgid_t cr_groups[NGROUPS];        /* Group membership for caller */
 368        };
 369
 370
 371  .. Note::
 372
 373     It is questionable if we need CodaCreds in Venus. Finally Venus
 374     doesn't know about groups, although it does create files with the
 375     default uid/gid.  Perhaps the list of group membership is superfluous.
 376
 377
 378  The next item is the fundamental identifier used to identify Coda
 379  files, the ViceFid.  A fid of a file uniquely defines a file or
 380  directory in the Coda filesystem within a cell [1]_::
 381
 382        typedef struct ViceFid {
 383            VolumeId Volume;
 384            VnodeId Vnode;
 385            Unique_t Unique;
 386        } ViceFid;
 387
 388  .. [1] A cell is agroup of Coda servers acting under the aegis of a single
 389         system control machine or SCM. See the Coda Administration manual
 390         for a detailed description of the role of the SCM.
 391
 392  Each of the constituent fields: VolumeId, VnodeId and Unique_t are
 393  unsigned 32 bit integers.  We envisage that a further field will need
 394  to be prefixed to identify the Coda cell; this will probably take the
 395  form of a Ipv6 size IP address naming the Coda cell through DNS.
 396
 397  The next important structure shared between Venus and the kernel is
 398  the attributes of the file.  The following structure is used to
 399  exchange information.  It has room for future extensions such as
 400  support for device files (currently not present in Coda)::
 401
 402
 403        struct coda_timespec {
 404                int64_t         tv_sec;         /* seconds */
 405                long            tv_nsec;        /* nanoseconds */
 406        };
 407
 408        struct coda_vattr {
 409                enum coda_vtype va_type;        /* vnode type (for create) */
 410                u_short         va_mode;        /* files access mode and type */
 411                short           va_nlink;       /* number of references to file */
 412                vuid_t          va_uid;         /* owner user id */
 413                vgid_t          va_gid;         /* owner group id */
 414                long            va_fsid;        /* file system id (dev for now) */
 415                long            va_fileid;      /* file id */
 416                u_quad_t        va_size;        /* file size in bytes */
 417                long            va_blocksize;   /* blocksize preferred for i/o */
 418                struct coda_timespec va_atime;  /* time of last access */
 419                struct coda_timespec va_mtime;  /* time of last modification */
 420                struct coda_timespec va_ctime;  /* time file changed */
 421                u_long          va_gen;         /* generation number of file */
 422                u_long          va_flags;       /* flags defined for file */
 423                dev_t           va_rdev;        /* device special file represents */
 424                u_quad_t        va_bytes;       /* bytes of disk space held by file */
 425                u_quad_t        va_filerev;     /* file modification number */
 426                u_int           va_vaflags;     /* operations flags, see below */
 427                long            va_spare;       /* remain quad aligned */
 428        };
 429
 430
 4314.2.  The pioctl interface
 432--------------------------
 433
 434
 435  Coda specific requests can be made by application through the pioctl
 436  interface. The pioctl is implemented as an ordinary ioctl on a
 437  fictitious file /coda/.CONTROL.  The pioctl call opens this file, gets
 438  a file handle and makes the ioctl call. Finally it closes the file.
 439
 440  The kernel involvement in this is limited to providing the facility to
 441  open and close and pass the ioctl message and to verify that a path in
 442  the pioctl data buffers is a file in a Coda filesystem.
 443
 444  The kernel is handed a data packet of the form::
 445
 446        struct {
 447            const char *path;
 448            struct ViceIoctl vidata;
 449            int follow;
 450        } data;
 451
 452
 453
 454  where::
 455
 456
 457        struct ViceIoctl {
 458                caddr_t in, out;        /* Data to be transferred in, or out */
 459                short in_size;          /* Size of input buffer <= 2K */
 460                short out_size;         /* Maximum size of output buffer, <= 2K */
 461        };
 462
 463
 464
 465  The path must be a Coda file, otherwise the ioctl upcall will not be
 466  made.
 467
 468  .. Note:: The data structures and code are a mess.  We need to clean this up.
 469
 470
 471**We now proceed to document the individual calls**:
 472
 473
 4744.3.  root
 475----------
 476
 477
 478  Arguments
 479     in
 480
 481        empty
 482
 483     out::
 484
 485                struct cfs_root_out {
 486                    ViceFid VFid;
 487                } cfs_root;
 488
 489
 490
 491  Description
 492    This call is made to Venus during the initialization of
 493    the Coda filesystem. If the result is zero, the cfs_root structure
 494    contains the ViceFid of the root of the Coda filesystem. If a non-zero
 495    result is generated, its value is a platform dependent error code
 496    indicating the difficulty Venus encountered in locating the root of
 497    the Coda filesystem.
 498
 4994.4.  lookup
 500------------
 501
 502
 503  Summary
 504    Find the ViceFid and type of an object in a directory if it exists.
 505
 506  Arguments
 507     in::
 508
 509                struct  cfs_lookup_in {
 510                    ViceFid     VFid;
 511                    char        *name;          /* Place holder for data. */
 512                } cfs_lookup;
 513
 514
 515
 516     out::
 517
 518                struct cfs_lookup_out {
 519                    ViceFid VFid;
 520                    int vtype;
 521                } cfs_lookup;
 522
 523
 524
 525  Description
 526    This call is made to determine the ViceFid and filetype of
 527    a directory entry.  The directory entry requested carries name 'name'
 528    and Venus will search the directory identified by cfs_lookup_in.VFid.
 529    The result may indicate that the name does not exist, or that
 530    difficulty was encountered in finding it (e.g. due to disconnection).
 531    If the result is zero, the field cfs_lookup_out.VFid contains the
 532    targets ViceFid and cfs_lookup_out.vtype the coda_vtype giving the
 533    type of object the name designates.
 534
 535  The name of the object is an 8 bit character string of maximum length
 536  CFS_MAXNAMLEN, currently set to 256 (including a 0 terminator.)
 537
 538  It is extremely important to realize that Venus bitwise ors the field
 539  cfs_lookup.vtype with CFS_NOCACHE to indicate that the object should
 540  not be put in the kernel name cache.
 541
 542  .. Note::
 543
 544     The type of the vtype is currently wrong.  It should be
 545     coda_vtype. Linux does not take note of CFS_NOCACHE.  It should.
 546
 547
 5484.5.  getattr
 549-------------
 550
 551
 552  Summary Get the attributes of a file.
 553
 554  Arguments
 555     in::
 556
 557                struct cfs_getattr_in {
 558                    ViceFid VFid;
 559                    struct coda_vattr attr; /* XXXXX */
 560                } cfs_getattr;
 561
 562
 563
 564     out::
 565
 566                struct cfs_getattr_out {
 567                    struct coda_vattr attr;
 568                } cfs_getattr;
 569
 570
 571
 572  Description
 573    This call returns the attributes of the file identified by fid.
 574
 575  Errors
 576    Errors can occur if the object with fid does not exist, is
 577    unaccessible or if the caller does not have permission to fetch
 578    attributes.
 579
 580  .. Note::
 581
 582     Many kernel FS drivers (Linux, NT and Windows 95) need to acquire
 583     the attributes as well as the Fid for the instantiation of an internal
 584     "inode" or "FileHandle".  A significant improvement in performance on
 585     such systems could be made by combining the lookup and getattr calls
 586     both at the Venus/kernel interaction level and at the RPC level.
 587
 588  The vattr structure included in the input arguments is superfluous and
 589  should be removed.
 590
 591
 5924.6.  setattr
 593-------------
 594
 595
 596  Summary
 597    Set the attributes of a file.
 598
 599  Arguments
 600     in::
 601
 602                struct cfs_setattr_in {
 603                    ViceFid VFid;
 604                    struct coda_vattr attr;
 605                } cfs_setattr;
 606
 607
 608
 609
 610     out
 611
 612        empty
 613
 614  Description
 615    The structure attr is filled with attributes to be changed
 616    in BSD style.  Attributes not to be changed are set to -1, apart from
 617    vtype which is set to VNON. Other are set to the value to be assigned.
 618    The only attributes which the FS driver may request to change are the
 619    mode, owner, groupid, atime, mtime and ctime.  The return value
 620    indicates success or failure.
 621
 622  Errors
 623    A variety of errors can occur.  The object may not exist, may
 624    be inaccessible, or permission may not be granted by Venus.
 625
 626
 6274.7.  access
 628------------
 629
 630
 631  Arguments
 632     in::
 633
 634                struct cfs_access_in {
 635                    ViceFid     VFid;
 636                    int flags;
 637                } cfs_access;
 638
 639
 640
 641     out
 642
 643        empty
 644
 645  Description
 646    Verify if access to the object identified by VFid for
 647    operations described by flags is permitted.  The result indicates if
 648    access will be granted.  It is important to remember that Coda uses
 649    ACLs to enforce protection and that ultimately the servers, not the
 650    clients enforce the security of the system.  The result of this call
 651    will depend on whether a token is held by the user.
 652
 653  Errors
 654    The object may not exist, or the ACL describing the protection
 655    may not be accessible.
 656
 657
 6584.8.  create
 659------------
 660
 661
 662  Summary
 663    Invoked to create a file
 664
 665  Arguments
 666     in::
 667
 668                struct cfs_create_in {
 669                    ViceFid VFid;
 670                    struct coda_vattr attr;
 671                    int excl;
 672                    int mode;
 673                    char        *name;          /* Place holder for data. */
 674                } cfs_create;
 675
 676
 677
 678
 679     out::
 680
 681                struct cfs_create_out {
 682                    ViceFid VFid;
 683                    struct coda_vattr attr;
 684                } cfs_create;
 685
 686
 687
 688  Description
 689    This upcall is invoked to request creation of a file.
 690    The file will be created in the directory identified by VFid, its name
 691    will be name, and the mode will be mode.  If excl is set an error will
 692    be returned if the file already exists.  If the size field in attr is
 693    set to zero the file will be truncated.  The uid and gid of the file
 694    are set by converting the CodaCred to a uid using a macro CRTOUID
 695    (this macro is platform dependent).  Upon success the VFid and
 696    attributes of the file are returned.  The Coda FS Driver will normally
 697    instantiate a vnode, inode or file handle at kernel level for the new
 698    object.
 699
 700
 701  Errors
 702    A variety of errors can occur. Permissions may be insufficient.
 703    If the object exists and is not a file the error EISDIR is returned
 704    under Unix.
 705
 706  .. Note::
 707
 708     The packing of parameters is very inefficient and appears to
 709     indicate confusion between the system call creat and the VFS operation
 710     create. The VFS operation create is only called to create new objects.
 711     This create call differs from the Unix one in that it is not invoked
 712     to return a file descriptor. The truncate and exclusive options,
 713     together with the mode, could simply be part of the mode as it is
 714     under Unix.  There should be no flags argument; this is used in open
 715     (2) to return a file descriptor for READ or WRITE mode.
 716
 717  The attributes of the directory should be returned too, since the size
 718  and mtime changed.
 719
 720
 7214.9.  mkdir
 722-----------
 723
 724
 725  Summary
 726    Create a new directory.
 727
 728  Arguments
 729     in::
 730
 731                struct cfs_mkdir_in {
 732                    ViceFid     VFid;
 733                    struct coda_vattr attr;
 734                    char        *name;          /* Place holder for data. */
 735                } cfs_mkdir;
 736
 737
 738
 739     out::
 740
 741                struct cfs_mkdir_out {
 742                    ViceFid VFid;
 743                    struct coda_vattr attr;
 744                } cfs_mkdir;
 745
 746
 747
 748
 749  Description
 750    This call is similar to create but creates a directory.
 751    Only the mode field in the input parameters is used for creation.
 752    Upon successful creation, the attr returned contains the attributes of
 753    the new directory.
 754
 755  Errors
 756    As for create.
 757
 758  .. Note::
 759
 760     The input parameter should be changed to mode instead of
 761     attributes.
 762
 763  The attributes of the parent should be returned since the size and
 764  mtime changes.
 765
 766
 7674.10.  link
 768-----------
 769
 770
 771  Summary
 772    Create a link to an existing file.
 773
 774  Arguments
 775     in::
 776
 777                struct cfs_link_in {
 778                    ViceFid sourceFid;          /* cnode to link *to* */
 779                    ViceFid destFid;            /* Directory in which to place link */
 780                    char        *tname;         /* Place holder for data. */
 781                } cfs_link;
 782
 783
 784
 785     out
 786
 787        empty
 788
 789  Description
 790    This call creates a link to the sourceFid in the directory
 791    identified by destFid with name tname.  The source must reside in the
 792    target's parent, i.e. the source must be have parent destFid, i.e. Coda
 793    does not support cross directory hard links.  Only the return value is
 794    relevant.  It indicates success or the type of failure.
 795
 796  Errors
 797    The usual errors can occur.
 798
 799
 8004.11.  symlink
 801--------------
 802
 803
 804  Summary
 805    create a symbolic link
 806
 807  Arguments
 808     in::
 809
 810                struct cfs_symlink_in {
 811                    ViceFid     VFid;          /* Directory to put symlink in */
 812                    char        *srcname;
 813                    struct coda_vattr attr;
 814                    char        *tname;
 815                } cfs_symlink;
 816
 817
 818
 819     out
 820
 821        none
 822
 823  Description
 824    Create a symbolic link. The link is to be placed in the
 825    directory identified by VFid and named tname.  It should point to the
 826    pathname srcname.  The attributes of the newly created object are to
 827    be set to attr.
 828
 829  .. Note::
 830
 831     The attributes of the target directory should be returned since
 832     its size changed.
 833
 834
 8354.12.  remove
 836-------------
 837
 838
 839  Summary
 840    Remove a file
 841
 842  Arguments
 843     in::
 844
 845                struct cfs_remove_in {
 846                    ViceFid     VFid;
 847                    char        *name;          /* Place holder for data. */
 848                } cfs_remove;
 849
 850
 851
 852     out
 853
 854        none
 855
 856  Description
 857    Remove file named cfs_remove_in.name in directory
 858    identified by   VFid.
 859
 860
 861  .. Note::
 862
 863     The attributes of the directory should be returned since its
 864     mtime and size may change.
 865
 866
 8674.13.  rmdir
 868------------
 869
 870
 871  Summary
 872    Remove a directory
 873
 874  Arguments
 875     in::
 876
 877                struct cfs_rmdir_in {
 878                    ViceFid     VFid;
 879                    char        *name;          /* Place holder for data. */
 880                } cfs_rmdir;
 881
 882
 883
 884     out
 885
 886        none
 887
 888  Description
 889    Remove the directory with name 'name' from the directory
 890    identified by VFid.
 891
 892  .. Note:: The attributes of the parent directory should be returned since
 893            its mtime and size may change.
 894
 895
 8964.14.  readlink
 897---------------
 898
 899
 900  Summary
 901    Read the value of a symbolic link.
 902
 903  Arguments
 904     in::
 905
 906                struct cfs_readlink_in {
 907                    ViceFid VFid;
 908                } cfs_readlink;
 909
 910
 911
 912     out::
 913
 914                struct cfs_readlink_out {
 915                    int count;
 916                    caddr_t     data;           /* Place holder for data. */
 917                } cfs_readlink;
 918
 919
 920
 921  Description
 922    This routine reads the contents of symbolic link
 923    identified by VFid into the buffer data.  The buffer data must be able
 924    to hold any name up to CFS_MAXNAMLEN (PATH or NAM??).
 925
 926  Errors
 927    No unusual errors.
 928
 929
 9304.15.  open
 931-----------
 932
 933
 934  Summary
 935    Open a file.
 936
 937  Arguments
 938     in::
 939
 940                struct cfs_open_in {
 941                    ViceFid     VFid;
 942                    int flags;
 943                } cfs_open;
 944
 945
 946
 947     out::
 948
 949                struct cfs_open_out {
 950                    dev_t       dev;
 951                    ino_t       inode;
 952                } cfs_open;
 953
 954
 955
 956  Description
 957    This request asks Venus to place the file identified by
 958    VFid in its cache and to note that the calling process wishes to open
 959    it with flags as in open(2).  The return value to the kernel differs
 960    for Unix and Windows systems.  For Unix systems the Coda FS Driver is
 961    informed of the device and inode number of the container file in the
 962    fields dev and inode.  For Windows the path of the container file is
 963    returned to the kernel.
 964
 965
 966  .. Note::
 967
 968     Currently the cfs_open_out structure is not properly adapted to
 969     deal with the Windows case.  It might be best to implement two
 970     upcalls, one to open aiming at a container file name, the other at a
 971     container file inode.
 972
 973
 9744.16.  close
 975------------
 976
 977
 978  Summary
 979    Close a file, update it on the servers.
 980
 981  Arguments
 982     in::
 983
 984                struct cfs_close_in {
 985                    ViceFid     VFid;
 986                    int flags;
 987                } cfs_close;
 988
 989
 990
 991     out
 992
 993        none
 994
 995  Description
 996    Close the file identified by VFid.
 997
 998  .. Note::
 999
1000     The flags argument is bogus and not used.  However, Venus' code
1001     has room to deal with an execp input field, probably this field should
1002     be used to inform Venus that the file was closed but is still memory
1003     mapped for execution.  There are comments about fetching versus not
1004     fetching the data in Venus vproc_vfscalls.  This seems silly.  If a
1005     file is being closed, the data in the container file is to be the new
1006     data.  Here again the execp flag might be in play to create confusion:
1007     currently Venus might think a file can be flushed from the cache when
1008     it is still memory mapped.  This needs to be understood.
1009
1010
10114.17.  ioctl
1012------------
1013
1014
1015  Summary
1016    Do an ioctl on a file. This includes the pioctl interface.
1017
1018  Arguments
1019     in::
1020
1021                struct cfs_ioctl_in {
1022                    ViceFid VFid;
1023                    int cmd;
1024                    int len;
1025                    int rwflag;
1026                    char *data;                 /* Place holder for data. */
1027                } cfs_ioctl;
1028
1029
1030
1031     out::
1032
1033
1034                struct cfs_ioctl_out {
1035                    int len;
1036                    caddr_t     data;           /* Place holder for data. */
1037                } cfs_ioctl;
1038
1039
1040
1041  Description
1042    Do an ioctl operation on a file.  The command, len and
1043    data arguments are filled as usual.  flags is not used by Venus.
1044
1045  .. Note::
1046
1047     Another bogus parameter.  flags is not used.  What is the
1048     business about PREFETCHING in the Venus code?
1049
1050
1051
10524.18.  rename
1053-------------
1054
1055
1056  Summary
1057    Rename a fid.
1058
1059  Arguments
1060     in::
1061
1062                struct cfs_rename_in {
1063                    ViceFid     sourceFid;
1064                    char        *srcname;
1065                    ViceFid destFid;
1066                    char        *destname;
1067                } cfs_rename;
1068
1069
1070
1071     out
1072
1073        none
1074
1075  Description
1076    Rename the object with name srcname in directory
1077    sourceFid to destname in destFid.   It is important that the names
1078    srcname and destname are 0 terminated strings.  Strings in Unix
1079    kernels are not always null terminated.
1080
1081
10824.19.  readdir
1083--------------
1084
1085
1086  Summary
1087    Read directory entries.
1088
1089  Arguments
1090     in::
1091
1092                struct cfs_readdir_in {
1093                    ViceFid     VFid;
1094                    int count;
1095                    int offset;
1096                } cfs_readdir;
1097
1098
1099
1100
1101     out::
1102
1103                struct cfs_readdir_out {
1104                    int size;
1105                    caddr_t     data;           /* Place holder for data. */
1106                } cfs_readdir;
1107
1108
1109
1110  Description
1111    Read directory entries from VFid starting at offset and
1112    read at most count bytes.  Returns the data in data and returns
1113    the size in size.
1114
1115
1116  .. Note::
1117
1118     This call is not used.  Readdir operations exploit container
1119     files.  We will re-evaluate this during the directory revamp which is
1120     about to take place.
1121
1122
11234.20.  vget
1124-----------
1125
1126
1127  Summary
1128    instructs Venus to do an FSDB->Get.
1129
1130  Arguments
1131     in::
1132
1133                struct cfs_vget_in {
1134                    ViceFid VFid;
1135                } cfs_vget;
1136
1137
1138
1139     out::
1140
1141                struct cfs_vget_out {
1142                    ViceFid VFid;
1143                    int vtype;
1144                } cfs_vget;
1145
1146
1147
1148  Description
1149    This upcall asks Venus to do a get operation on an fsobj
1150    labelled by VFid.
1151
1152  .. Note::
1153
1154     This operation is not used.  However, it is extremely useful
1155     since it can be used to deal with read/write memory mapped files.
1156     These can be "pinned" in the Venus cache using vget and released with
1157     inactive.
1158
1159
11604.21.  fsync
1161------------
1162
1163
1164  Summary
1165    Tell Venus to update the RVM attributes of a file.
1166
1167  Arguments
1168     in::
1169
1170                struct cfs_fsync_in {
1171                    ViceFid VFid;
1172                } cfs_fsync;
1173
1174
1175
1176     out
1177
1178        none
1179
1180  Description
1181    Ask Venus to update RVM attributes of object VFid. This
1182    should be called as part of kernel level fsync type calls.  The
1183    result indicates if the syncing was successful.
1184
1185  .. Note:: Linux does not implement this call. It should.
1186
1187
11884.22.  inactive
1189---------------
1190
1191
1192  Summary
1193    Tell Venus a vnode is no longer in use.
1194
1195  Arguments
1196     in::
1197
1198                struct cfs_inactive_in {
1199                    ViceFid VFid;
1200                } cfs_inactive;
1201
1202
1203
1204     out
1205
1206        none
1207
1208  Description
1209    This operation returns EOPNOTSUPP.
1210
1211  .. Note:: This should perhaps be removed.
1212
1213
12144.23.  rdwr
1215-----------
1216
1217
1218  Summary
1219    Read or write from a file
1220
1221  Arguments
1222     in::
1223
1224                struct cfs_rdwr_in {
1225                    ViceFid     VFid;
1226                    int rwflag;
1227                    int count;
1228                    int offset;
1229                    int ioflag;
1230                    caddr_t     data;           /* Place holder for data. */
1231                } cfs_rdwr;
1232
1233
1234
1235
1236     out::
1237
1238                struct cfs_rdwr_out {
1239                    int rwflag;
1240                    int count;
1241                    caddr_t     data;   /* Place holder for data. */
1242                } cfs_rdwr;
1243
1244
1245
1246  Description
1247    This upcall asks Venus to read or write from a file.
1248
1249
1250  .. Note::
1251
1252    It should be removed since it is against the Coda philosophy that
1253    read/write operations never reach Venus.  I have been told the
1254    operation does not work.  It is not currently used.
1255
1256
1257
12584.24.  odymount
1259---------------
1260
1261
1262  Summary
1263    Allows mounting multiple Coda "filesystems" on one Unix mount point.
1264
1265  Arguments
1266     in::
1267
1268                struct ody_mount_in {
1269                    char        *name;          /* Place holder for data. */
1270                } ody_mount;
1271
1272
1273
1274     out::
1275
1276                struct ody_mount_out {
1277                    ViceFid VFid;
1278                } ody_mount;
1279
1280
1281
1282  Description
1283    Asks Venus to return the rootfid of a Coda system named
1284    name.  The fid is returned in VFid.
1285
1286  .. Note::
1287
1288     This call was used by David for dynamic sets.  It should be
1289     removed since it causes a jungle of pointers in the VFS mounting area.
1290     It is not used by Coda proper.  Call is not implemented by Venus.
1291
1292
12934.25.  ody_lookup
1294-----------------
1295
1296
1297  Summary
1298    Looks up something.
1299
1300  Arguments
1301     in
1302
1303        irrelevant
1304
1305
1306     out
1307
1308        irrelevant
1309
1310
1311  .. Note:: Gut it. Call is not implemented by Venus.
1312
1313
13144.26.  ody_expand
1315-----------------
1316
1317
1318  Summary
1319    expands something in a dynamic set.
1320
1321  Arguments
1322     in
1323
1324        irrelevant
1325
1326     out
1327
1328        irrelevant
1329
1330  .. Note:: Gut it. Call is not implemented by Venus.
1331
1332
13334.27.  prefetch
1334---------------
1335
1336
1337  Summary
1338    Prefetch a dynamic set.
1339
1340  Arguments
1341
1342     in
1343
1344        Not documented.
1345
1346     out
1347
1348        Not documented.
1349
1350  Description
1351    Venus worker.cc has support for this call, although it is
1352    noted that it doesn't work.  Not surprising, since the kernel does not
1353    have support for it. (ODY_PREFETCH is not a defined operation).
1354
1355
1356  .. Note:: Gut it. It isn't working and isn't used by Coda.
1357
1358
1359
13604.28.  signal
1361-------------
1362
1363
1364  Summary
1365    Send Venus a signal about an upcall.
1366
1367  Arguments
1368     in
1369
1370        none
1371
1372     out
1373
1374        not applicable.
1375
1376  Description
1377    This is an out-of-band upcall to Venus to inform Venus
1378    that the calling process received a signal after Venus read the
1379    message from the input queue.  Venus is supposed to clean up the
1380    operation.
1381
1382  Errors
1383    No reply is given.
1384
1385  .. Note::
1386
1387     We need to better understand what Venus needs to clean up and if
1388     it is doing this correctly.  Also we need to handle multiple upcall
1389     per system call situations correctly.  It would be important to know
1390     what state changes in Venus take place after an upcall for which the
1391     kernel is responsible for notifying Venus to clean up (e.g. open
1392     definitely is such a state change, but many others are maybe not).
1393
1394
13955.  The minicache and downcalls
1396===============================
1397
1398
1399  The Coda FS Driver can cache results of lookup and access upcalls, to
1400  limit the frequency of upcalls.  Upcalls carry a price since a process
1401  context switch needs to take place.  The counterpart of caching the
1402  information is that Venus will notify the FS Driver that cached
1403  entries must be flushed or renamed.
1404
1405  The kernel code generally has to maintain a structure which links the
1406  internal file handles (called vnodes in BSD, inodes in Linux and
1407  FileHandles in Windows) with the ViceFid's which Venus maintains.  The
1408  reason is that frequent translations back and forth are needed in
1409  order to make upcalls and use the results of upcalls.  Such linking
1410  objects are called cnodes.
1411
1412  The current minicache implementations have cache entries which record
1413  the following:
1414
1415  1. the name of the file
1416
1417  2. the cnode of the directory containing the object
1418
1419  3. a list of CodaCred's for which the lookup is permitted.
1420
1421  4. the cnode of the object
1422
1423  The lookup call in the Coda FS Driver may request the cnode of the
1424  desired object from the cache, by passing its name, directory and the
1425  CodaCred's of the caller.  The cache will return the cnode or indicate
1426  that it cannot be found.  The Coda FS Driver must be careful to
1427  invalidate cache entries when it modifies or removes objects.
1428
1429  When Venus obtains information that indicates that cache entries are
1430  no longer valid, it will make a downcall to the kernel.  Downcalls are
1431  intercepted by the Coda FS Driver and lead to cache invalidations of
1432  the kind described below.  The Coda FS Driver does not return an error
1433  unless the downcall data could not be read into kernel memory.
1434
1435
14365.1.  INVALIDATE
1437----------------
1438
1439
1440  No information is available on this call.
1441
1442
14435.2.  FLUSH
1444-----------
1445
1446
1447
1448  Arguments
1449    None
1450
1451  Summary
1452    Flush the name cache entirely.
1453
1454  Description
1455    Venus issues this call upon startup and when it dies. This
1456    is to prevent stale cache information being held.  Some operating
1457    systems allow the kernel name cache to be switched off dynamically.
1458    When this is done, this downcall is made.
1459
1460
14615.3.  PURGEUSER
1462---------------
1463
1464
1465  Arguments
1466    ::
1467
1468          struct cfs_purgeuser_out {/* CFS_PURGEUSER is a venus->kernel call */
1469              struct CodaCred cred;
1470          } cfs_purgeuser;
1471
1472
1473
1474  Description
1475    Remove all entries in the cache carrying the Cred.  This
1476    call is issued when tokens for a user expire or are flushed.
1477
1478
14795.4.  ZAPFILE
1480-------------
1481
1482
1483  Arguments
1484    ::
1485
1486          struct cfs_zapfile_out {  /* CFS_ZAPFILE is a venus->kernel call */
1487              ViceFid CodaFid;
1488          } cfs_zapfile;
1489
1490
1491
1492  Description
1493    Remove all entries which have the (dir vnode, name) pair.
1494    This is issued as a result of an invalidation of cached attributes of
1495    a vnode.
1496
1497  .. Note::
1498
1499     Call is not named correctly in NetBSD and Mach.  The minicache
1500     zapfile routine takes different arguments. Linux does not implement
1501     the invalidation of attributes correctly.
1502
1503
1504
15055.5.  ZAPDIR
1506------------
1507
1508
1509  Arguments
1510    ::
1511
1512          struct cfs_zapdir_out {   /* CFS_ZAPDIR is a venus->kernel call */
1513              ViceFid CodaFid;
1514          } cfs_zapdir;
1515
1516
1517
1518  Description
1519    Remove all entries in the cache lying in a directory
1520    CodaFid, and all children of this directory. This call is issued when
1521    Venus receives a callback on the directory.
1522
1523
15245.6.  ZAPVNODE
1525--------------
1526
1527
1528
1529  Arguments
1530    ::
1531
1532          struct cfs_zapvnode_out { /* CFS_ZAPVNODE is a venus->kernel call */
1533              struct CodaCred cred;
1534              ViceFid VFid;
1535          } cfs_zapvnode;
1536
1537
1538
1539  Description
1540    Remove all entries in the cache carrying the cred and VFid
1541    as in the arguments. This downcall is probably never issued.
1542
1543
15445.7.  PURGEFID
1545--------------
1546
1547
1548  Arguments
1549    ::
1550
1551          struct cfs_purgefid_out { /* CFS_PURGEFID is a venus->kernel call */
1552              ViceFid CodaFid;
1553          } cfs_purgefid;
1554
1555
1556
1557  Description
1558    Flush the attribute for the file. If it is a dir (odd
1559    vnode), purge its children from the namecache and remove the file from the
1560    namecache.
1561
1562
1563
15645.8.  REPLACE
1565-------------
1566
1567
1568  Summary
1569    Replace the Fid's for a collection of names.
1570
1571  Arguments
1572    ::
1573
1574          struct cfs_replace_out { /* cfs_replace is a venus->kernel call */
1575              ViceFid NewFid;
1576              ViceFid OldFid;
1577          } cfs_replace;
1578
1579
1580
1581  Description
1582    This routine replaces a ViceFid in the name cache with
1583    another.  It is added to allow Venus during reintegration to replace
1584    locally allocated temp fids while disconnected with global fids even
1585    when the reference counts on those fids are not zero.
1586
1587
15886.  Initialization and cleanup
1589==============================
1590
1591
1592  This section gives brief hints as to desirable features for the Coda
1593  FS Driver at startup and upon shutdown or Venus failures.  Before
1594  entering the discussion it is useful to repeat that the Coda FS Driver
1595  maintains the following data:
1596
1597
1598  1. message queues
1599
1600  2. cnodes
1601
1602  3. name cache entries
1603
1604     The name cache entries are entirely private to the driver, so they
1605     can easily be manipulated.   The message queues will generally have
1606     clear points of initialization and destruction.  The cnodes are
1607     much more delicate.  User processes hold reference counts in Coda
1608     filesystems and it can be difficult to clean up the cnodes.
1609
1610  It can expect requests through:
1611
1612  1. the message subsystem
1613
1614  2. the VFS layer
1615
1616  3. pioctl interface
1617
1618     Currently the pioctl passes through the VFS for Coda so we can
1619     treat these similarly.
1620
1621
16226.1.  Requirements
1623------------------
1624
1625
1626  The following requirements should be accommodated:
1627
1628  1. The message queues should have open and close routines.  On Unix
1629     the opening of the character devices are such routines.
1630
1631    -  Before opening, no messages can be placed.
1632
1633    -  Opening will remove any old messages still pending.
1634
1635    -  Close will notify any sleeping processes that their upcall cannot
1636       be completed.
1637
1638    -  Close will free all memory allocated by the message queues.
1639
1640
1641  2. At open the namecache shall be initialized to empty state.
1642
1643  3. Before the message queues are open, all VFS operations will fail.
1644     Fortunately this can be achieved by making sure than mounting the
1645     Coda filesystem cannot succeed before opening.
1646
1647  4. After closing of the queues, no VFS operations can succeed.  Here
1648     one needs to be careful, since a few operations (lookup,
1649     read/write, readdir) can proceed without upcalls.  These must be
1650     explicitly blocked.
1651
1652  5. Upon closing the namecache shall be flushed and disabled.
1653
1654  6. All memory held by cnodes can be freed without relying on upcalls.
1655
1656  7. Unmounting the file system can be done without relying on upcalls.
1657
1658  8. Mounting the Coda filesystem should fail gracefully if Venus cannot
1659     get the rootfid or the attributes of the rootfid.  The latter is
1660     best implemented by Venus fetching these objects before attempting
1661     to mount.
1662
1663  .. Note::
1664
1665     NetBSD in particular but also Linux have not implemented the
1666     above requirements fully.  For smooth operation this needs to be
1667     corrected.
1668
1669
1670
1671