linux/Documentation/filesystems/coda.txt
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   1NOTE: 
   2This is one of the technical documents describing a component of
   3Coda -- this document describes the client kernel-Venus interface.
   4
   5For more information:
   6  http://www.coda.cs.cmu.edu
   7For user level software needed to run Coda:
   8  ftp://ftp.coda.cs.cmu.edu
   9
  10To run Coda you need to get a user level cache manager for the client,
  11named Venus, as well as tools to manipulate ACLs, to log in, etc.  The
  12client needs to have the Coda filesystem selected in the kernel
  13configuration.
  14
  15The server needs a user level server and at present does not depend on
  16kernel support.
  17
  18
  19
  20
  21
  22
  23
  24  The Venus kernel interface
  25  Peter J. Braam
  26  v1.0, Nov 9, 1997
  27
  28  This document describes the communication between Venus and kernel
  29  level filesystem code needed for the operation of the Coda file sys-
  30  tem.  This document version is meant to describe the current interface
  31  (version 1.0) as well as improvements we envisage.
  32  ______________________________________________________________________
  33
  34  Table of Contents
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  90  1. Introduction
  91
  92  2. Servicing Coda filesystem calls
  93
  94  3. The message layer
  95
  96     3.1 Implementation details
  97
  98  4. The interface at the call level
  99
 100     4.1 Data structures shared by the kernel and Venus
 101     4.2 The pioctl interface
 102     4.3 root
 103     4.4 lookup
 104     4.5 getattr
 105     4.6 setattr
 106     4.7 access
 107     4.8 create
 108     4.9 mkdir
 109     4.10 link
 110     4.11 symlink
 111     4.12 remove
 112     4.13 rmdir
 113     4.14 readlink
 114     4.15 open
 115     4.16 close
 116     4.17 ioctl
 117     4.18 rename
 118     4.19 readdir
 119     4.20 vget
 120     4.21 fsync
 121     4.22 inactive
 122     4.23 rdwr
 123     4.24 odymount
 124     4.25 ody_lookup
 125     4.26 ody_expand
 126     4.27 prefetch
 127     4.28 signal
 128
 129  5. The minicache and downcalls
 130
 131     5.1 INVALIDATE
 132     5.2 FLUSH
 133     5.3 PURGEUSER
 134     5.4 ZAPFILE
 135     5.5 ZAPDIR
 136     5.6 ZAPVNODE
 137     5.7 PURGEFID
 138     5.8 REPLACE
 139
 140  6. Initialization and cleanup
 141
 142     6.1 Requirements
 143
 144
 145  ______________________________________________________________________
 146  0wpage
 147
 148  11..  IInnttrroodduuccttiioonn
 149
 150
 151
 152  A key component in the Coda Distributed File System is the cache
 153  manager, _V_e_n_u_s.
 154
 155
 156  When processes on a Coda enabled system access files in the Coda
 157  filesystem, requests are directed at the filesystem layer in the
 158  operating system. The operating system will communicate with Venus to
 159  service the request for the process.  Venus manages a persistent
 160  client cache and makes remote procedure calls to Coda file servers and
 161  related servers (such as authentication servers) to service these
 162  requests it receives from the operating system.  When Venus has
 163  serviced a request it replies to the operating system with appropriate
 164  return codes, and other data related to the request.  Optionally the
 165  kernel support for Coda may maintain a minicache of recently processed
 166  requests to limit the number of interactions with Venus.  Venus
 167  possesses the facility to inform the kernel when elements from its
 168  minicache are no longer valid.
 169
 170  This document describes precisely this communication between the
 171  kernel and Venus.  The definitions of so called upcalls and downcalls
 172  will be given with the format of the data they handle. We shall also
 173  describe the semantic invariants resulting from the calls.
 174
 175  Historically Coda was implemented in a BSD file system in Mach 2.6.
 176  The interface between the kernel and Venus is very similar to the BSD
 177  VFS interface.  Similar functionality is provided, and the format of
 178  the parameters and returned data is very similar to the BSD VFS.  This
 179  leads to an almost natural environment for implementing a kernel-level
 180  filesystem driver for Coda in a BSD system.  However, other operating
 181  systems such as Linux and Windows 95 and NT have virtual filesystem
 182  with different interfaces.
 183
 184  To implement Coda on these systems some reverse engineering of the
 185  Venus/Kernel protocol is necessary.  Also it came to light that other
 186  systems could profit significantly from certain small optimizations
 187  and modifications to the protocol. To facilitate this work as well as
 188  to make future ports easier, communication between Venus and the
 189  kernel should be documented in great detail.  This is the aim of this
 190  document.
 191
 192  0wpage
 193
 194  22..  SSeerrvviicciinngg CCooddaa ffiilleessyysstteemm ccaallllss
 195
 196  The service of a request for a Coda file system service originates in
 197  a process PP which accessing a Coda file. It makes a system call which
 198  traps to the OS kernel. Examples of such calls trapping to the kernel
 199  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
 200  context.  Similar calls exist in the Win32 environment, and are named
 201  _C_r_e_a_t_e_F_i_l_e_, .
 202
 203  Generally the operating system handles the request in a virtual
 204  filesystem (VFS) layer, which is named I/O Manager in NT and IFS
 205  manager in Windows 95.  The VFS is responsible for partial processing
 206  of the request and for locating the specific filesystem(s) which will
 207  service parts of the request.  Usually the information in the path
 208  assists in locating the correct FS drivers.  Sometimes after extensive
 209  pre-processing, the VFS starts invoking exported routines in the FS
 210  driver.  This is the point where the FS specific processing of the
 211  request starts, and here the Coda specific kernel code comes into
 212  play.
 213
 214  The FS layer for Coda must expose and implement several interfaces.
 215  First and foremost the VFS must be able to make all necessary calls to
 216  the Coda FS layer, so the Coda FS driver must expose the VFS interface
 217  as applicable in the operating system. These differ very significantly
 218  among operating systems, but share features such as facilities to
 219  read/write and create and remove objects.  The Coda FS layer services
 220  such VFS requests by invoking one or more well defined services
 221  offered by the cache manager Venus.  When the replies from Venus have
 222  come back to the FS driver, servicing of the VFS call continues and
 223  finishes with a reply to the kernel's VFS. Finally the VFS layer
 224  returns to the process.
 225
 226  As a result of this design a basic interface exposed by the FS driver
 227  must allow Venus to manage message traffic.  In particular Venus must
 228  be able to retrieve and place messages and to be notified of the
 229  arrival of a new message. The notification must be through a mechanism
 230  which does not block Venus since Venus must attend to other tasks even
 231  when no messages are waiting or being processed.
 232
 233
 234
 235
 236
 237
 238                     Interfaces of the Coda FS Driver
 239
 240  Furthermore the FS layer provides for a special path of communication
 241  between a user process and Venus, called the pioctl interface. The
 242  pioctl interface is used for Coda specific services, such as
 243  requesting detailed information about the persistent cache managed by
 244  Venus. Here the involvement of the kernel is minimal.  It identifies
 245  the calling process and passes the information on to Venus.  When
 246  Venus replies the response is passed back to the caller in unmodified
 247  form.
 248
 249  Finally Venus allows the kernel FS driver to cache the results from
 250  certain services.  This is done to avoid excessive context switches
 251  and results in an efficient system.  However, Venus may acquire
 252  information, for example from the network which implies that cached
 253  information must be flushed or replaced. Venus then makes a downcall
 254  to the Coda FS layer to request flushes or updates in the cache.  The
 255  kernel FS driver handles such requests synchronously.
 256
 257  Among these interfaces the VFS interface and the facility to place,
 258  receive and be notified of messages are platform specific.  We will
 259  not go into the calls exported to the VFS layer but we will state the
 260  requirements of the message exchange mechanism.
 261
 262  0wpage
 263
 264  33..  TThhee mmeessssaaggee llaayyeerr
 265
 266
 267
 268  At the lowest level the communication between Venus and the FS driver
 269  proceeds through messages.  The synchronization between processes
 270  requesting Coda file service and Venus relies on blocking and waking
 271  up processes.  The Coda FS driver processes VFS- and pioctl-requests
 272  on behalf of a process P, creates messages for Venus, awaits replies
 273  and finally returns to the caller.  The implementation of the exchange
 274  of messages is platform specific, but the semantics have (so far)
 275  appeared to be generally applicable.  Data buffers are created by the
 276  FS Driver in kernel memory on behalf of P and copied to user memory in
 277  Venus.
 278
 279  The FS Driver while servicing P makes upcalls to Venus.  Such an
 280  upcall is dispatched to Venus by creating a message structure.  The
 281  structure contains the identification of P, the message sequence
 282  number, the size of the request and a pointer to the data in kernel
 283  memory for the request.  Since the data buffer is re-used to hold the
 284  reply from Venus, there is a field for the size of the reply.  A flags
 285  field is used in the message to precisely record the status of the
 286  message.  Additional platform dependent structures involve pointers to
 287  determine the position of the message on queues and pointers to
 288  synchronization objects.  In the upcall routine the message structure
 289  is filled in, flags are set to 0, and it is placed on the _p_e_n_d_i_n_g
 290  queue.  The routine calling upcall is responsible for allocating the
 291  data buffer; its structure will be described in the next section.
 292
 293  A facility must exist to notify Venus that the message has been
 294  created, and implemented using available synchronization objects in
 295  the OS. This notification is done in the upcall context of the process
 296  P. When the message is on the pending queue, process P cannot proceed
 297  in upcall.  The (kernel mode) processing of P in the filesystem
 298  request routine must be suspended until Venus has replied.  Therefore
 299  the calling thread in P is blocked in upcall.  A pointer in the
 300  message structure will locate the synchronization object on which P is
 301  sleeping.
 302
 303  Venus detects the notification that a message has arrived, and the FS
 304  driver allow Venus to retrieve the message with a getmsg_from_kernel
 305  call. This action finishes in the kernel by putting the message on the
 306  queue of processing messages and setting flags to READ.  Venus is
 307  passed the contents of the data buffer. The getmsg_from_kernel call
 308  now returns and Venus processes the request.
 309
 310  At some later point the FS driver receives a message from Venus,
 311  namely when Venus calls sendmsg_to_kernel.  At this moment the Coda FS
 312  driver looks at the contents of the message and decides if:
 313
 314
 315  +o  the message is a reply for a suspended thread P.  If so it removes
 316     the message from the processing queue and marks the message as
 317     WRITTEN.  Finally, the FS driver unblocks P (still in the kernel
 318     mode context of Venus) and the sendmsg_to_kernel call returns to
 319     Venus.  The process P will be scheduled at some point and continues
 320     processing its upcall with the data buffer replaced with the reply
 321     from Venus.
 322
 323  +o  The message is a _d_o_w_n_c_a_l_l.  A downcall is a request from Venus to
 324     the FS Driver. The FS driver processes the request immediately
 325     (usually a cache eviction or replacement) and when it finishes
 326     sendmsg_to_kernel returns.
 327
 328  Now P awakes and continues processing upcall.  There are some
 329  subtleties to take account of. First P will determine if it was woken
 330  up in upcall by a signal from some other source (for example an
 331  attempt to terminate P) or as is normally the case by Venus in its
 332  sendmsg_to_kernel call.  In the normal case, the upcall routine will
 333  deallocate the message structure and return.  The FS routine can proceed
 334  with its processing.
 335
 336
 337
 338
 339
 340
 341
 342                      Sleeping and IPC arrangements
 343
 344  In case P is woken up by a signal and not by Venus, it will first look
 345  at the flags field.  If the message is not yet READ, the process P can
 346  handle its signal without notifying Venus.  If Venus has READ, and
 347  the request should not be processed, P can send Venus a signal message
 348  to indicate that it should disregard the previous message.  Such
 349  signals are put in the queue at the head, and read first by Venus.  If
 350  the message is already marked as WRITTEN it is too late to stop the
 351  processing.  The VFS routine will now continue.  (-- If a VFS request
 352  involves more than one upcall, this can lead to complicated state, an
 353  extra field "handle_signals" could be added in the message structure
 354  to indicate points of no return have been passed.--)
 355
 356
 357
 358  33..11..  IImmpplleemmeennttaattiioonn ddeettaaiillss
 359
 360  The Unix implementation of this mechanism has been through the
 361  implementation of a character device associated with Coda.  Venus
 362  retrieves messages by doing a read on the device, replies are sent
 363  with a write and notification is through the select system call on the
 364  file descriptor for the device.  The process P is kept waiting on an
 365  interruptible wait queue object.
 366
 367  In Windows NT and the DPMI Windows 95 implementation a DeviceIoControl
 368  call is used.  The DeviceIoControl call is designed to copy buffers
 369  from user memory to kernel memory with OPCODES. The sendmsg_to_kernel
 370  is issued as a synchronous call, while the getmsg_from_kernel call is
 371  asynchronous.  Windows EventObjects are used for notification of
 372  message arrival.  The process P is kept waiting on a KernelEvent
 373  object in NT and a semaphore in Windows 95.
 374
 375  0wpage
 376
 377  44..  TThhee iinntteerrffaaccee aatt tthhee ccaallll lleevveell
 378
 379
 380  This section describes the upcalls a Coda FS driver can make to Venus.
 381  Each of these upcalls make use of two structures: inputArgs and
 382  outputArgs.   In pseudo BNF form the structures take the following
 383  form:
 384
 385
 386  struct inputArgs {
 387      u_long opcode;
 388      u_long unique;     /* Keep multiple outstanding msgs distinct */
 389      u_short pid;                 /* Common to all */
 390      u_short pgid;                /* Common to all */
 391      struct CodaCred cred;        /* Common to all */
 392
 393      <union "in" of call dependent parts of inputArgs>
 394  };
 395
 396  struct outputArgs {
 397      u_long opcode;
 398      u_long unique;       /* Keep multiple outstanding msgs distinct */
 399      u_long result;
 400
 401      <union "out" of call dependent parts of inputArgs>
 402  };
 403
 404
 405
 406  Before going on let us elucidate the role of the various fields. The
 407  inputArgs start with the opcode which defines the type of service
 408  requested from Venus. There are approximately 30 upcalls at present
 409  which we will discuss.   The unique field labels the inputArg with a
 410  unique number which will identify the message uniquely.  A process and
 411  process group id are passed.  Finally the credentials of the caller
 412  are included.
 413
 414  Before delving into the specific calls we need to discuss a variety of
 415  data structures shared by the kernel and Venus.
 416
 417
 418
 419
 420  44..11..  DDaattaa ssttrruuccttuurreess sshhaarreedd bbyy tthhee kkeerrnneell aanndd VVeennuuss
 421
 422
 423  The CodaCred structure defines a variety of user and group ids as
 424  they are set for the calling process. The vuid_t and guid_t are 32 bit
 425  unsigned integers.  It also defines group membership in an array.  On
 426  Unix the CodaCred has proven sufficient to implement good security
 427  semantics for Coda but the structure may have to undergo modification
 428  for the Windows environment when these mature.
 429
 430  struct CodaCred {
 431      vuid_t cr_uid, cr_euid, cr_suid, cr_fsuid; /* Real, effective, set, fs uid*/
 432      vgid_t cr_gid, cr_egid, cr_sgid, cr_fsgid; /* same for groups */
 433      vgid_t cr_groups[NGROUPS];        /* Group membership for caller */
 434  };
 435
 436
 437
 438  NNOOTTEE It is questionable if we need CodaCreds in Venus. Finally Venus
 439  doesn't know about groups, although it does create files with the
 440  default uid/gid.  Perhaps the list of group membership is superfluous.
 441
 442
 443  The next item is the fundamental identifier used to identify Coda
 444  files, the ViceFid.  A fid of a file uniquely defines a file or
 445  directory in the Coda filesystem within a _c_e_l_l.   (-- A _c_e_l_l is a
 446  group of Coda servers acting under the aegis of a single system
 447  control machine or SCM. See the Coda Administration manual for a
 448  detailed description of the role of the SCM.--)
 449
 450
 451  typedef struct ViceFid {
 452      VolumeId Volume;
 453      VnodeId Vnode;
 454      Unique_t Unique;
 455  } ViceFid;
 456
 457
 458
 459  Each of the constituent fields: VolumeId, VnodeId and Unique_t are
 460  unsigned 32 bit integers.  We envisage that a further field will need
 461  to be prefixed to identify the Coda cell; this will probably take the
 462  form of a Ipv6 size IP address naming the Coda cell through DNS.
 463
 464  The next important structure shared between Venus and the kernel is
 465  the attributes of the file.  The following structure is used to
 466  exchange information.  It has room for future extensions such as
 467  support for device files (currently not present in Coda).
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486  struct coda_vattr {
 487          enum coda_vtype va_type;        /* vnode type (for create) */
 488          u_short         va_mode;        /* files access mode and type */
 489          short           va_nlink;       /* number of references to file */
 490          vuid_t          va_uid;         /* owner user id */
 491          vgid_t          va_gid;         /* owner group id */
 492          long            va_fsid;        /* file system id (dev for now) */
 493          long            va_fileid;      /* file id */
 494          u_quad_t        va_size;        /* file size in bytes */
 495          long            va_blocksize;   /* blocksize preferred for i/o */
 496          struct timespec va_atime;       /* time of last access */
 497          struct timespec va_mtime;       /* time of last modification */
 498          struct timespec va_ctime;       /* time file changed */
 499          u_long          va_gen;         /* generation number of file */
 500          u_long          va_flags;       /* flags defined for file */
 501          dev_t           va_rdev;        /* device special file represents */
 502          u_quad_t        va_bytes;       /* bytes of disk space held by file */
 503          u_quad_t        va_filerev;     /* file modification number */
 504          u_int           va_vaflags;     /* operations flags, see below */
 505          long            va_spare;       /* remain quad aligned */
 506  };
 507
 508
 509
 510
 511  44..22..  TThhee ppiiooccttll iinntteerrffaaccee
 512
 513
 514  Coda specific requests can be made by application through the pioctl
 515  interface. The pioctl is implemented as an ordinary ioctl on a
 516  fictitious file /coda/.CONTROL.  The pioctl call opens this file, gets
 517  a file handle and makes the ioctl call. Finally it closes the file.
 518
 519  The kernel involvement in this is limited to providing the facility to
 520  open and close and pass the ioctl message _a_n_d to verify that a path in
 521  the pioctl data buffers is a file in a Coda filesystem.
 522
 523  The kernel is handed a data packet of the form:
 524
 525      struct {
 526          const char *path;
 527          struct ViceIoctl vidata;
 528          int follow;
 529      } data;
 530
 531
 532
 533  where
 534
 535
 536  struct ViceIoctl {
 537          caddr_t in, out;        /* Data to be transferred in, or out */
 538          short in_size;          /* Size of input buffer <= 2K */
 539          short out_size;         /* Maximum size of output buffer, <= 2K */
 540  };
 541
 542
 543
 544  The path must be a Coda file, otherwise the ioctl upcall will not be
 545  made.
 546
 547  NNOOTTEE  The data structures and code are a mess.  We need to clean this
 548  up.
 549
 550  We now proceed to document the individual calls:
 551
 552  0wpage
 553
 554  44..33..  rroooott
 555
 556
 557  AArrgguummeennttss
 558
 559     iinn empty
 560
 561     oouutt
 562
 563                struct cfs_root_out {
 564                    ViceFid VFid;
 565                } cfs_root;
 566
 567
 568
 569  DDeessccrriippttiioonn This call is made to Venus during the initialization of
 570  the Coda filesystem. If the result is zero, the cfs_root structure
 571  contains the ViceFid of the root of the Coda filesystem. If a non-zero
 572  result is generated, its value is a platform dependent error code
 573  indicating the difficulty Venus encountered in locating the root of
 574  the Coda filesystem.
 575
 576  0wpage
 577
 578  44..44..  llooookkuupp
 579
 580
 581  SSuummmmaarryy Find the ViceFid and type of an object in a directory if it
 582  exists.
 583
 584  AArrgguummeennttss
 585
 586     iinn
 587
 588                struct  cfs_lookup_in {
 589                    ViceFid     VFid;
 590                    char        *name;          /* Place holder for data. */
 591                } cfs_lookup;
 592
 593
 594
 595     oouutt
 596
 597                struct cfs_lookup_out {
 598                    ViceFid VFid;
 599                    int vtype;
 600                } cfs_lookup;
 601
 602
 603
 604  DDeessccrriippttiioonn This call is made to determine the ViceFid and filetype of
 605  a directory entry.  The directory entry requested carries name name
 606  and Venus will search the directory identified by cfs_lookup_in.VFid.
 607  The result may indicate that the name does not exist, or that
 608  difficulty was encountered in finding it (e.g. due to disconnection).
 609  If the result is zero, the field cfs_lookup_out.VFid contains the
 610  targets ViceFid and cfs_lookup_out.vtype the coda_vtype giving the
 611  type of object the name designates.
 612
 613  The name of the object is an 8 bit character string of maximum length
 614  CFS_MAXNAMLEN, currently set to 256 (including a 0 terminator.)
 615
 616  It is extremely important to realize that Venus bitwise ors the field
 617  cfs_lookup.vtype with CFS_NOCACHE to indicate that the object should
 618  not be put in the kernel name cache.
 619
 620  NNOOTTEE The type of the vtype is currently wrong.  It should be
 621  coda_vtype. Linux does not take note of CFS_NOCACHE.  It should.
 622
 623  0wpage
 624
 625  44..55..  ggeettaattttrr
 626
 627
 628  SSuummmmaarryy Get the attributes of a file.
 629
 630  AArrgguummeennttss
 631
 632     iinn
 633
 634                struct cfs_getattr_in {
 635                    ViceFid VFid;
 636                    struct coda_vattr attr; /* XXXXX */
 637                } cfs_getattr;
 638
 639
 640
 641     oouutt
 642
 643                struct cfs_getattr_out {
 644                    struct coda_vattr attr;
 645                } cfs_getattr;
 646
 647
 648
 649  DDeessccrriippttiioonn This call returns the attributes of the file identified by
 650  fid.
 651
 652  EErrrroorrss Errors can occur if the object with fid does not exist, is
 653  unaccessible or if the caller does not have permission to fetch
 654  attributes.
 655
 656  NNoottee Many kernel FS drivers (Linux, NT and Windows 95) need to acquire
 657  the attributes as well as the Fid for the instantiation of an internal
 658  "inode" or "FileHandle".  A significant improvement in performance on
 659  such systems could be made by combining the _l_o_o_k_u_p and _g_e_t_a_t_t_r calls
 660  both at the Venus/kernel interaction level and at the RPC level.
 661
 662  The vattr structure included in the input arguments is superfluous and
 663  should be removed.
 664
 665  0wpage
 666
 667  44..66..  sseettaattttrr
 668
 669
 670  SSuummmmaarryy Set the attributes of a file.
 671
 672  AArrgguummeennttss
 673
 674     iinn
 675
 676                struct cfs_setattr_in {
 677                    ViceFid VFid;
 678                    struct coda_vattr attr;
 679                } cfs_setattr;
 680
 681
 682
 683
 684     oouutt
 685        empty
 686
 687  DDeessccrriippttiioonn The structure attr is filled with attributes to be changed
 688  in BSD style.  Attributes not to be changed are set to -1, apart from
 689  vtype which is set to VNON. Other are set to the value to be assigned.
 690  The only attributes which the FS driver may request to change are the
 691  mode, owner, groupid, atime, mtime and ctime.  The return value
 692  indicates success or failure.
 693
 694  EErrrroorrss A variety of errors can occur.  The object may not exist, may
 695  be inaccessible, or permission may not be granted by Venus.
 696
 697  0wpage
 698
 699  44..77..  aacccceessss
 700
 701
 702  SSuummmmaarryy
 703
 704  AArrgguummeennttss
 705
 706     iinn
 707
 708                struct cfs_access_in {
 709                    ViceFid     VFid;
 710                    int flags;
 711                } cfs_access;
 712
 713
 714
 715     oouutt
 716        empty
 717
 718  DDeessccrriippttiioonn Verify if access to the object identified by VFid for
 719  operations described by flags is permitted.  The result indicates if
 720  access will be granted.  It is important to remember that Coda uses
 721  ACLs to enforce protection and that ultimately the servers, not the
 722  clients enforce the security of the system.  The result of this call
 723  will depend on whether a _t_o_k_e_n is held by the user.
 724
 725  EErrrroorrss The object may not exist, or the ACL describing the protection
 726  may not be accessible.
 727
 728  0wpage
 729
 730  44..88..  ccrreeaattee
 731
 732
 733  SSuummmmaarryy Invoked to create a file
 734
 735  AArrgguummeennttss
 736
 737     iinn
 738
 739                struct cfs_create_in {
 740                    ViceFid VFid;
 741                    struct coda_vattr attr;
 742                    int excl;
 743                    int mode;
 744                    char        *name;          /* Place holder for data. */
 745                } cfs_create;
 746
 747
 748
 749
 750     oouutt
 751
 752                struct cfs_create_out {
 753                    ViceFid VFid;
 754                    struct coda_vattr attr;
 755                } cfs_create;
 756
 757
 758
 759  DDeessccrriippttiioonn  This upcall is invoked to request creation of a file.
 760  The file will be created in the directory identified by VFid, its name
 761  will be name, and the mode will be mode.  If excl is set an error will
 762  be returned if the file already exists.  If the size field in attr is
 763  set to zero the file will be truncated.  The uid and gid of the file
 764  are set by converting the CodaCred to a uid using a macro CRTOUID
 765  (this macro is platform dependent).  Upon success the VFid and
 766  attributes of the file are returned.  The Coda FS Driver will normally
 767  instantiate a vnode, inode or file handle at kernel level for the new
 768  object.
 769
 770
 771  EErrrroorrss A variety of errors can occur. Permissions may be insufficient.
 772  If the object exists and is not a file the error EISDIR is returned
 773  under Unix.
 774
 775  NNOOTTEE The packing of parameters is very inefficient and appears to
 776  indicate confusion between the system call creat and the VFS operation
 777  create. The VFS operation create is only called to create new objects.
 778  This create call differs from the Unix one in that it is not invoked
 779  to return a file descriptor. The truncate and exclusive options,
 780  together with the mode, could simply be part of the mode as it is
 781  under Unix.  There should be no flags argument; this is used in open
 782  (2) to return a file descriptor for READ or WRITE mode.
 783
 784  The attributes of the directory should be returned too, since the size
 785  and mtime changed.
 786
 787  0wpage
 788
 789  44..99..  mmkkddiirr
 790
 791
 792  SSuummmmaarryy Create a new directory.
 793
 794  AArrgguummeennttss
 795
 796     iinn
 797
 798                struct cfs_mkdir_in {
 799                    ViceFid     VFid;
 800                    struct coda_vattr attr;
 801                    char        *name;          /* Place holder for data. */
 802                } cfs_mkdir;
 803
 804
 805
 806     oouutt
 807
 808                struct cfs_mkdir_out {
 809                    ViceFid VFid;
 810                    struct coda_vattr attr;
 811                } cfs_mkdir;
 812
 813
 814
 815
 816  DDeessccrriippttiioonn This call is similar to create but creates a directory.
 817  Only the mode field in the input parameters is used for creation.
 818  Upon successful creation, the attr returned contains the attributes of
 819  the new directory.
 820
 821  EErrrroorrss As for create.
 822
 823  NNOOTTEE The input parameter should be changed to mode instead of
 824  attributes.
 825
 826  The attributes of the parent should be returned since the size and
 827  mtime changes.
 828
 829  0wpage
 830
 831  44..1100..  lliinnkk
 832
 833
 834  SSuummmmaarryy Create a link to an existing file.
 835
 836  AArrgguummeennttss
 837
 838     iinn
 839
 840                struct cfs_link_in {
 841                    ViceFid sourceFid;          /* cnode to link *to* */
 842                    ViceFid destFid;            /* Directory in which to place link */
 843                    char        *tname;         /* Place holder for data. */
 844                } cfs_link;
 845
 846
 847
 848     oouutt
 849        empty
 850
 851  DDeessccrriippttiioonn This call creates a link to the sourceFid in the directory
 852  identified by destFid with name tname.  The source must reside in the
 853  target's parent, i.e. the source must be have parent destFid, i.e. Coda
 854  does not support cross directory hard links.  Only the return value is
 855  relevant.  It indicates success or the type of failure.
 856
 857  EErrrroorrss The usual errors can occur.0wpage
 858
 859  44..1111..  ssyymmlliinnkk
 860
 861
 862  SSuummmmaarryy create a symbolic link
 863
 864  AArrgguummeennttss
 865
 866     iinn
 867
 868                struct cfs_symlink_in {
 869                    ViceFid     VFid;          /* Directory to put symlink in */
 870                    char        *srcname;
 871                    struct coda_vattr attr;
 872                    char        *tname;
 873                } cfs_symlink;
 874
 875
 876
 877     oouutt
 878        none
 879
 880  DDeessccrriippttiioonn Create a symbolic link. The link is to be placed in the
 881  directory identified by VFid and named tname.  It should point to the
 882  pathname srcname.  The attributes of the newly created object are to
 883  be set to attr.
 884
 885  EErrrroorrss
 886
 887  NNOOTTEE The attributes of the target directory should be returned since
 888  its size changed.
 889
 890  0wpage
 891
 892  44..1122..  rreemmoovvee
 893
 894
 895  SSuummmmaarryy Remove a file
 896
 897  AArrgguummeennttss
 898
 899     iinn
 900
 901                struct cfs_remove_in {
 902                    ViceFid     VFid;
 903                    char        *name;          /* Place holder for data. */
 904                } cfs_remove;
 905
 906
 907
 908     oouutt
 909        none
 910
 911  DDeessccrriippttiioonn  Remove file named cfs_remove_in.name in directory
 912  identified by   VFid.
 913
 914  EErrrroorrss
 915
 916  NNOOTTEE The attributes of the directory should be returned since its
 917  mtime and size may change.
 918
 919  0wpage
 920
 921  44..1133..  rrmmddiirr
 922
 923
 924  SSuummmmaarryy Remove a directory
 925
 926  AArrgguummeennttss
 927
 928     iinn
 929
 930                struct cfs_rmdir_in {
 931                    ViceFid     VFid;
 932                    char        *name;          /* Place holder for data. */
 933                } cfs_rmdir;
 934
 935
 936
 937     oouutt
 938        none
 939
 940  DDeessccrriippttiioonn Remove the directory with name name from the directory
 941  identified by VFid.
 942
 943  EErrrroorrss
 944
 945  NNOOTTEE The attributes of the parent directory should be returned since
 946  its mtime and size may change.
 947
 948  0wpage
 949
 950  44..1144..  rreeaaddlliinnkk
 951
 952
 953  SSuummmmaarryy Read the value of a symbolic link.
 954
 955  AArrgguummeennttss
 956
 957     iinn
 958
 959                struct cfs_readlink_in {
 960                    ViceFid VFid;
 961                } cfs_readlink;
 962
 963
 964
 965     oouutt
 966
 967                struct cfs_readlink_out {
 968                    int count;
 969                    caddr_t     data;           /* Place holder for data. */
 970                } cfs_readlink;
 971
 972
 973
 974  DDeessccrriippttiioonn This routine reads the contents of symbolic link
 975  identified by VFid into the buffer data.  The buffer data must be able
 976  to hold any name up to CFS_MAXNAMLEN (PATH or NAM??).
 977
 978  EErrrroorrss No unusual errors.
 979
 980  0wpage
 981
 982  44..1155..  ooppeenn
 983
 984
 985  SSuummmmaarryy Open a file.
 986
 987  AArrgguummeennttss
 988
 989     iinn
 990
 991                struct cfs_open_in {
 992                    ViceFid     VFid;
 993                    int flags;
 994                } cfs_open;
 995
 996
 997
 998     oouutt
 999
1000                struct cfs_open_out {
1001                    dev_t       dev;
1002                    ino_t       inode;
1003                } cfs_open;
1004
1005
1006
1007  DDeessccrriippttiioonn  This request asks Venus to place the file identified by
1008  VFid in its cache and to note that the calling process wishes to open
1009  it with flags as in open(2).  The return value to the kernel differs
1010  for Unix and Windows systems.  For Unix systems the Coda FS Driver is
1011  informed of the device and inode number of the container file in the
1012  fields dev and inode.  For Windows the path of the container file is
1013  returned to the kernel.
1014  EErrrroorrss
1015
1016  NNOOTTEE Currently the cfs_open_out structure is not properly adapted to
1017  deal with the Windows case.  It might be best to implement two
1018  upcalls, one to open aiming at a container file name, the other at a
1019  container file inode.
1020
1021  0wpage
1022
1023  44..1166..  cclloossee
1024
1025
1026  SSuummmmaarryy Close a file, update it on the servers.
1027
1028  AArrgguummeennttss
1029
1030     iinn
1031
1032                struct cfs_close_in {
1033                    ViceFid     VFid;
1034                    int flags;
1035                } cfs_close;
1036
1037
1038
1039     oouutt
1040        none
1041
1042  DDeessccrriippttiioonn Close the file identified by VFid.
1043
1044  EErrrroorrss
1045
1046  NNOOTTEE The flags argument is bogus and not used.  However, Venus' code
1047  has room to deal with an execp input field, probably this field should
1048  be used to inform Venus that the file was closed but is still memory
1049  mapped for execution.  There are comments about fetching versus not
1050  fetching the data in Venus vproc_vfscalls.  This seems silly.  If a
1051  file is being closed, the data in the container file is to be the new
1052  data.  Here again the execp flag might be in play to create confusion:
1053  currently Venus might think a file can be flushed from the cache when
1054  it is still memory mapped.  This needs to be understood.
1055
1056  0wpage
1057
1058  44..1177..  iiooccttll
1059
1060
1061  SSuummmmaarryy Do an ioctl on a file. This includes the pioctl interface.
1062
1063  AArrgguummeennttss
1064
1065     iinn
1066
1067                struct cfs_ioctl_in {
1068                    ViceFid VFid;
1069                    int cmd;
1070                    int len;
1071                    int rwflag;
1072                    char *data;                 /* Place holder for data. */
1073                } cfs_ioctl;
1074
1075
1076
1077     oouutt
1078
1079
1080                struct cfs_ioctl_out {
1081                    int len;
1082                    caddr_t     data;           /* Place holder for data. */
1083                } cfs_ioctl;
1084
1085
1086
1087  DDeessccrriippttiioonn Do an ioctl operation on a file.  The command, len and
1088  data arguments are filled as usual.  flags is not used by Venus.
1089
1090  EErrrroorrss
1091
1092  NNOOTTEE Another bogus parameter.  flags is not used.  What is the
1093  business about PREFETCHING in the Venus code?
1094
1095
1096  0wpage
1097
1098  44..1188..  rreennaammee
1099
1100
1101  SSuummmmaarryy Rename a fid.
1102
1103  AArrgguummeennttss
1104
1105     iinn
1106
1107                struct cfs_rename_in {
1108                    ViceFid     sourceFid;
1109                    char        *srcname;
1110                    ViceFid destFid;
1111                    char        *destname;
1112                } cfs_rename;
1113
1114
1115
1116     oouutt
1117        none
1118
1119  DDeessccrriippttiioonn  Rename the object with name srcname in directory
1120  sourceFid to destname in destFid.   It is important that the names
1121  srcname and destname are 0 terminated strings.  Strings in Unix
1122  kernels are not always null terminated.
1123
1124  EErrrroorrss
1125
1126  0wpage
1127
1128  44..1199..  rreeaaddddiirr
1129
1130
1131  SSuummmmaarryy Read directory entries.
1132
1133  AArrgguummeennttss
1134
1135     iinn
1136
1137                struct cfs_readdir_in {
1138                    ViceFid     VFid;
1139                    int count;
1140                    int offset;
1141                } cfs_readdir;
1142
1143
1144
1145
1146     oouutt
1147
1148                struct cfs_readdir_out {
1149                    int size;
1150                    caddr_t     data;           /* Place holder for data. */
1151                } cfs_readdir;
1152
1153
1154
1155  DDeessccrriippttiioonn Read directory entries from VFid starting at offset and
1156  read at most count bytes.  Returns the data in data and returns
1157  the size in size.
1158
1159  EErrrroorrss
1160
1161  NNOOTTEE This call is not used.  Readdir operations exploit container
1162  files.  We will re-evaluate this during the directory revamp which is
1163  about to take place.
1164
1165  0wpage
1166
1167  44..2200..  vvggeett
1168
1169
1170  SSuummmmaarryy instructs Venus to do an FSDB->Get.
1171
1172  AArrgguummeennttss
1173
1174     iinn
1175
1176                struct cfs_vget_in {
1177                    ViceFid VFid;
1178                } cfs_vget;
1179
1180
1181
1182     oouutt
1183
1184                struct cfs_vget_out {
1185                    ViceFid VFid;
1186                    int vtype;
1187                } cfs_vget;
1188
1189
1190
1191  DDeessccrriippttiioonn This upcall asks Venus to do a get operation on an fsobj
1192  labelled by VFid.
1193
1194  EErrrroorrss
1195
1196  NNOOTTEE This operation is not used.  However, it is extremely useful
1197  since it can be used to deal with read/write memory mapped files.
1198  These can be "pinned" in the Venus cache using vget and released with
1199  inactive.
1200
1201  0wpage
1202
1203  44..2211..  ffssyynncc
1204
1205
1206  SSuummmmaarryy Tell Venus to update the RVM attributes of a file.
1207
1208  AArrgguummeennttss
1209
1210     iinn
1211
1212                struct cfs_fsync_in {
1213                    ViceFid VFid;
1214                } cfs_fsync;
1215
1216
1217
1218     oouutt
1219        none
1220
1221  DDeessccrriippttiioonn Ask Venus to update RVM attributes of object VFid. This
1222  should be called as part of kernel level fsync type calls.  The
1223  result indicates if the syncing was successful.
1224
1225  EErrrroorrss
1226
1227  NNOOTTEE Linux does not implement this call. It should.
1228
1229  0wpage
1230
1231  44..2222..  iinnaaccttiivvee
1232
1233
1234  SSuummmmaarryy Tell Venus a vnode is no longer in use.
1235
1236  AArrgguummeennttss
1237
1238     iinn
1239
1240                struct cfs_inactive_in {
1241                    ViceFid VFid;
1242                } cfs_inactive;
1243
1244
1245
1246     oouutt
1247        none
1248
1249  DDeessccrriippttiioonn This operation returns EOPNOTSUPP.
1250
1251  EErrrroorrss
1252
1253  NNOOTTEE This should perhaps be removed.
1254
1255  0wpage
1256
1257  44..2233..  rrddwwrr
1258
1259
1260  SSuummmmaarryy Read or write from a file
1261
1262  AArrgguummeennttss
1263
1264     iinn
1265
1266                struct cfs_rdwr_in {
1267                    ViceFid     VFid;
1268                    int rwflag;
1269                    int count;
1270                    int offset;
1271                    int ioflag;
1272                    caddr_t     data;           /* Place holder for data. */
1273                } cfs_rdwr;
1274
1275
1276
1277
1278     oouutt
1279
1280                struct cfs_rdwr_out {
1281                    int rwflag;
1282                    int count;
1283                    caddr_t     data;   /* Place holder for data. */
1284                } cfs_rdwr;
1285
1286
1287
1288  DDeessccrriippttiioonn This upcall asks Venus to read or write from a file.
1289
1290  EErrrroorrss
1291
1292  NNOOTTEE It should be removed since it is against the Coda philosophy that
1293  read/write operations never reach Venus.  I have been told the
1294  operation does not work.  It is not currently used.
1295
1296
1297  0wpage
1298
1299  44..2244..  ooddyymmoouunntt
1300
1301
1302  SSuummmmaarryy Allows mounting multiple Coda "filesystems" on one Unix mount
1303  point.
1304
1305  AArrgguummeennttss
1306
1307     iinn
1308
1309                struct ody_mount_in {
1310                    char        *name;          /* Place holder for data. */
1311                } ody_mount;
1312
1313
1314
1315     oouutt
1316
1317                struct ody_mount_out {
1318                    ViceFid VFid;
1319                } ody_mount;
1320
1321
1322
1323  DDeessccrriippttiioonn  Asks Venus to return the rootfid of a Coda system named
1324  name.  The fid is returned in VFid.
1325
1326  EErrrroorrss
1327
1328  NNOOTTEE This call was used by David for dynamic sets.  It should be
1329  removed since it causes a jungle of pointers in the VFS mounting area.
1330  It is not used by Coda proper.  Call is not implemented by Venus.
1331
1332  0wpage
1333
1334  44..2255..  ooddyy__llooookkuupp
1335
1336
1337  SSuummmmaarryy Looks up something.
1338
1339  AArrgguummeennttss
1340
1341     iinn irrelevant
1342
1343
1344     oouutt
1345        irrelevant
1346
1347  DDeessccrriippttiioonn
1348
1349  EErrrroorrss
1350
1351  NNOOTTEE Gut it. Call is not implemented by Venus.
1352
1353  0wpage
1354
1355  44..2266..  ooddyy__eexxppaanndd
1356
1357
1358  SSuummmmaarryy expands something in a dynamic set.
1359
1360  AArrgguummeennttss
1361
1362     iinn irrelevant
1363
1364     oouutt
1365        irrelevant
1366
1367  DDeessccrriippttiioonn
1368
1369  EErrrroorrss
1370
1371  NNOOTTEE Gut it.  Call is not implemented by Venus.
1372
1373  0wpage
1374
1375  44..2277..  pprreeffeettcchh
1376
1377
1378  SSuummmmaarryy Prefetch a dynamic set.
1379
1380  AArrgguummeennttss
1381
1382     iinn Not documented.
1383
1384     oouutt
1385        Not documented.
1386
1387  DDeessccrriippttiioonn  Venus worker.cc has support for this call, although it is
1388  noted that it doesn't work.  Not surprising, since the kernel does not
1389  have support for it. (ODY_PREFETCH is not a defined operation).
1390
1391  EErrrroorrss
1392
1393  NNOOTTEE Gut it. It isn't working and isn't used by Coda.
1394
1395
1396  0wpage
1397
1398  44..2288..  ssiiggnnaall
1399
1400
1401  SSuummmmaarryy Send Venus a signal about an upcall.
1402
1403  AArrgguummeennttss
1404
1405     iinn none
1406
1407     oouutt
1408        not applicable.
1409
1410  DDeessccrriippttiioonn  This is an out-of-band upcall to Venus to inform Venus
1411  that the calling process received a signal after Venus read the
1412  message from the input queue.  Venus is supposed to clean up the
1413  operation.
1414
1415  EErrrroorrss No reply is given.
1416
1417  NNOOTTEE We need to better understand what Venus needs to clean up and if
1418  it is doing this correctly.  Also we need to handle multiple upcall
1419  per system call situations correctly.  It would be important to know
1420  what state changes in Venus take place after an upcall for which the
1421  kernel is responsible for notifying Venus to clean up (e.g. open
1422  definitely is such a state change, but many others are maybe not).
1423
1424  0wpage
1425
1426  55..  TThhee mmiinniiccaacchhee aanndd ddoowwnnccaallllss
1427
1428
1429  The Coda FS Driver can cache results of lookup and access upcalls, to
1430  limit the frequency of upcalls.  Upcalls carry a price since a process
1431  context switch needs to take place.  The counterpart of caching the
1432  information is that Venus will notify the FS Driver that cached
1433  entries must be flushed or renamed.
1434
1435  The kernel code generally has to maintain a structure which links the
1436  internal file handles (called vnodes in BSD, inodes in Linux and
1437  FileHandles in Windows) with the ViceFid's which Venus maintains.  The
1438  reason is that frequent translations back and forth are needed in
1439  order to make upcalls and use the results of upcalls.  Such linking
1440  objects are called ccnnooddeess.
1441
1442  The current minicache implementations have cache entries which record
1443  the following:
1444
1445  1. the name of the file
1446
1447  2. the cnode of the directory containing the object
1448
1449  3. a list of CodaCred's for which the lookup is permitted.
1450
1451  4. the cnode of the object
1452
1453  The lookup call in the Coda FS Driver may request the cnode of the
1454  desired object from the cache, by passing its name, directory and the
1455  CodaCred's of the caller.  The cache will return the cnode or indicate
1456  that it cannot be found.  The Coda FS Driver must be careful to
1457  invalidate cache entries when it modifies or removes objects.
1458
1459  When Venus obtains information that indicates that cache entries are
1460  no longer valid, it will make a downcall to the kernel.  Downcalls are
1461  intercepted by the Coda FS Driver and lead to cache invalidations of
1462  the kind described below.  The Coda FS Driver does not return an error
1463  unless the downcall data could not be read into kernel memory.
1464
1465
1466  55..11..  IINNVVAALLIIDDAATTEE
1467
1468
1469  No information is available on this call.
1470
1471
1472  55..22..  FFLLUUSSHH
1473
1474
1475
1476  AArrgguummeennttss None
1477
1478  SSuummmmaarryy Flush the name cache entirely.
1479
1480  DDeessccrriippttiioonn Venus issues this call upon startup and when it dies. This
1481  is to prevent stale cache information being held.  Some operating
1482  systems allow the kernel name cache to be switched off dynamically.
1483  When this is done, this downcall is made.
1484
1485
1486  55..33..  PPUURRGGEEUUSSEERR
1487
1488
1489  AArrgguummeennttss
1490
1491          struct cfs_purgeuser_out {/* CFS_PURGEUSER is a venus->kernel call */
1492              struct CodaCred cred;
1493          } cfs_purgeuser;
1494
1495
1496
1497  DDeessccrriippttiioonn Remove all entries in the cache carrying the Cred.  This
1498  call is issued when tokens for a user expire or are flushed.
1499
1500
1501  55..44..  ZZAAPPFFIILLEE
1502
1503
1504  AArrgguummeennttss
1505
1506          struct cfs_zapfile_out {  /* CFS_ZAPFILE is a venus->kernel call */
1507              ViceFid CodaFid;
1508          } cfs_zapfile;
1509
1510
1511
1512  DDeessccrriippttiioonn Remove all entries which have the (dir vnode, name) pair.
1513  This is issued as a result of an invalidation of cached attributes of
1514  a vnode.
1515
1516  NNOOTTEE Call is not named correctly in NetBSD and Mach.  The minicache
1517  zapfile routine takes different arguments. Linux does not implement
1518  the invalidation of attributes correctly.
1519
1520
1521
1522  55..55..  ZZAAPPDDIIRR
1523
1524
1525  AArrgguummeennttss
1526
1527          struct cfs_zapdir_out {   /* CFS_ZAPDIR is a venus->kernel call */
1528              ViceFid CodaFid;
1529          } cfs_zapdir;
1530
1531
1532
1533  DDeessccrriippttiioonn Remove all entries in the cache lying in a directory
1534  CodaFid, and all children of this directory. This call is issued when
1535  Venus receives a callback on the directory.
1536
1537
1538  55..66..  ZZAAPPVVNNOODDEE
1539
1540
1541
1542  AArrgguummeennttss
1543
1544          struct cfs_zapvnode_out { /* CFS_ZAPVNODE is a venus->kernel call */
1545              struct CodaCred cred;
1546              ViceFid VFid;
1547          } cfs_zapvnode;
1548
1549
1550
1551  DDeessccrriippttiioonn Remove all entries in the cache carrying the cred and VFid
1552  as in the arguments. This downcall is probably never issued.
1553
1554
1555  55..77..  PPUURRGGEEFFIIDD
1556
1557
1558  SSuummmmaarryy
1559
1560  AArrgguummeennttss
1561
1562          struct cfs_purgefid_out { /* CFS_PURGEFID is a venus->kernel call */
1563              ViceFid CodaFid;
1564          } cfs_purgefid;
1565
1566
1567
1568  DDeessccrriippttiioonn Flush the attribute for the file. If it is a dir (odd
1569  vnode), purge its children from the namecache and remove the file from the
1570  namecache.
1571
1572
1573
1574  55..88..  RREEPPLLAACCEE
1575
1576
1577  SSuummmmaarryy Replace the Fid's for a collection of names.
1578
1579  AArrgguummeennttss
1580
1581          struct cfs_replace_out { /* cfs_replace is a venus->kernel call */
1582              ViceFid NewFid;
1583              ViceFid OldFid;
1584          } cfs_replace;
1585
1586
1587
1588  DDeessccrriippttiioonn This routine replaces a ViceFid in the name cache with
1589  another.  It is added to allow Venus during reintegration to replace
1590  locally allocated temp fids while disconnected with global fids even
1591  when the reference counts on those fids are not zero.
1592
1593  0wpage
1594
1595  66..  IInniittiiaalliizzaattiioonn aanndd cclleeaannuupp
1596
1597
1598  This section gives brief hints as to desirable features for the Coda
1599  FS Driver at startup and upon shutdown or Venus failures.  Before
1600  entering the discussion it is useful to repeat that the Coda FS Driver
1601  maintains the following data:
1602
1603
1604  1. message queues
1605
1606  2. cnodes
1607
1608  3. name cache entries
1609
1610     The name cache entries are entirely private to the driver, so they
1611     can easily be manipulated.   The message queues will generally have
1612     clear points of initialization and destruction.  The cnodes are
1613     much more delicate.  User processes hold reference counts in Coda
1614     filesystems and it can be difficult to clean up the cnodes.
1615
1616  It can expect requests through:
1617
1618  1. the message subsystem
1619
1620  2. the VFS layer
1621
1622  3. pioctl interface
1623
1624     Currently the _p_i_o_c_t_l passes through the VFS for Coda so we can
1625     treat these similarly.
1626
1627
1628  66..11..  RReeqquuiirreemmeennttss
1629
1630
1631  The following requirements should be accommodated:
1632
1633  1. The message queues should have open and close routines.  On Unix
1634     the opening of the character devices are such routines.
1635
1636  +o  Before opening, no messages can be placed.
1637
1638  +o  Opening will remove any old messages still pending.
1639
1640  +o  Close will notify any sleeping processes that their upcall cannot
1641     be completed.
1642
1643  +o  Close will free all memory allocated by the message queues.
1644
1645
1646  2. At open the namecache shall be initialized to empty state.
1647
1648  3. Before the message queues are open, all VFS operations will fail.
1649     Fortunately this can be achieved by making sure than mounting the
1650     Coda filesystem cannot succeed before opening.
1651
1652  4. After closing of the queues, no VFS operations can succeed.  Here
1653     one needs to be careful, since a few operations (lookup,
1654     read/write, readdir) can proceed without upcalls.  These must be
1655     explicitly blocked.
1656
1657  5. Upon closing the namecache shall be flushed and disabled.
1658
1659  6. All memory held by cnodes can be freed without relying on upcalls.
1660
1661  7. Unmounting the file system can be done without relying on upcalls.
1662
1663  8. Mounting the Coda filesystem should fail gracefully if Venus cannot
1664     get the rootfid or the attributes of the rootfid.  The latter is
1665     best implemented by Venus fetching these objects before attempting
1666     to mount.
1667
1668  NNOOTTEE  NetBSD in particular but also Linux have not implemented the
1669  above requirements fully.  For smooth operation this needs to be
1670  corrected.
1671
1672
1673
1674
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