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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:02 EST.

1	NOTE: 
2	This is one of the technical documents describing a component of
3	Coda -- this document describes the client kernel-Venus interface.
4	
5	For more information:
6	  http://www.coda.cs.cmu.edu
7	For user level software needed to run Coda:
8	  ftp://ftp.coda.cs.cmu.edu
9	
10	To run Coda you need to get a user level cache manager for the client,
11	named Venus, as well as tools to manipulate ACLs, to log in, etc.  The
12	client needs to have the Coda filesystem selected in the kernel
13	configuration.
14	
15	The server needs a user level server and at present does not depend on
16	kernel 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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89	
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	
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