1 .. SPDX-License-Identifier: GPL-2.0
2
3 ===========================
4 Coda Kernel-Venus Interface
5 ===========================
6
7 .. Note::
8
9 This is one of the technical documents describing a component of
10 Coda -- this document describes the client kernel-Venus interface.
11
12 For more information:
13
14 http://www.coda.cs.cmu.edu
15
16 For user level software needed to run Coda:
17
18 ftp://ftp.coda.cs.cmu.edu
19
20 To run Coda you need to get a user level cache manager for the client,
21 named Venus, as well as tools to manipulate ACLs, to log in, etc. The
22 client needs to have the Coda filesystem selected in the kernel
23 configuration.
24
25 The server needs a user level server and at present does not depend on
26 kernel support.
27
28 The Venus kernel interface
29
30 Peter J. Braam
31
32 v1.0, Nov 9, 1997
33
34 This document describes the communication between Venus and kernel
35 level filesystem code needed for the operation of the Coda file sys-
36 tem. This document version is meant to describe the current interface
37 (version 1.0) as well as improvements we envisage.
38
39 .. Table of Contents
40
41 1. Introduction
42
43 2. Servicing Coda filesystem calls
44
45 3. The message layer
46
47 3.1 Implementation details
48
49 4. The interface at the call level
50
51 4.1 Data structures shared by the kernel and Venus
52 4.2 The pioctl interface
53 4.3 root
54 4.4 lookup
55 4.5 getattr
56 4.6 setattr
57 4.7 access
58 4.8 create
59 4.9 mkdir
60 4.10 link
61 4.11 symlink
62 4.12 remove
63 4.13 rmdir
64 4.14 readlink
65 4.15 open
66 4.16 close
67 4.17 ioctl
68 4.18 rename
69 4.19 readdir
70 4.20 vget
71 4.21 fsync
72 4.22 inactive
73 4.23 rdwr
74 4.24 odymount
75 4.25 ody_lookup
76 4.26 ody_expand
77 4.27 prefetch
78 4.28 signal
79
80 5. The minicache and downcalls
81
82 5.1 INVALIDATE
83 5.2 FLUSH
84 5.3 PURGEUSER
85 5.4 ZAPFILE
86 5.5 ZAPDIR
87 5.6 ZAPVNODE
88 5.7 PURGEFID
89 5.8 REPLACE
90
91 6. Initialization and cleanup
92
93 6.1 Requirements
94
95 1. Introduction
96 ===============
97
98 A key component in the Coda Distributed File System is the cache
99 manager, Venus.
100
101 When processes on a Coda enabled system access files in the Coda
102 filesystem, requests are directed at the filesystem layer in the
103 operating system. The operating system will communicate with Venus to
104 service the request for the process. Venus manages a persistent
105 client cache and makes remote procedure calls to Coda file servers and
106 related servers (such as authentication servers) to service these
107 requests it receives from the operating system. When Venus has
108 serviced a request it replies to the operating system with appropriate
109 return codes, and other data related to the request. Optionally the
110 kernel support for Coda may maintain a minicache of recently processed
111 requests to limit the number of interactions with Venus. Venus
112 possesses the facility to inform the kernel when elements from its
113 minicache are no longer valid.
114
115 This document describes precisely this communication between the
116 kernel and Venus. The definitions of so called upcalls and downcalls
117 will be given with the format of the data they handle. We shall also
118 describe the semantic invariants resulting from the calls.
119
120 Historically Coda was implemented in a BSD file system in Mach 2.6.
121 The interface between the kernel and Venus is very similar to the BSD
122 VFS interface. Similar functionality is provided, and the format of
123 the parameters and returned data is very similar to the BSD VFS. This
124 leads to an almost natural environment for implementing a kernel-level
125 filesystem driver for Coda in a BSD system. However, other operating
126 systems such as Linux and Windows 95 and NT have virtual filesystem
127 with different interfaces.
128
129 To implement Coda on these systems some reverse engineering of the
130 Venus/Kernel protocol is necessary. Also it came to light that other
131 systems could profit significantly from certain small optimizations
132 and modifications to the protocol. To facilitate this work as well as
133 to make future ports easier, communication between Venus and the
134 kernel should be documented in great detail. This is the aim of this
135 document.
136
137 2. Servicing Coda filesystem calls
138 ===================================
139
140 The service of a request for a Coda file system service originates in
141 a process P which accessing a Coda file. It makes a system call which
142 traps to the OS kernel. Examples of such calls trapping to the kernel
143 are ``read``, ``write``, ``open``, ``close``, ``create``, ``mkdir``,
144 ``rmdir``, ``chmod`` in a Unix ontext. Similar calls exist in the Win32
145 environment, and are named ``CreateFile``.
146
147 Generally the operating system handles the request in a virtual
148 filesystem (VFS) layer, which is named I/O Manager in NT and IFS
149 manager in Windows 95. The VFS is responsible for partial processing
150 of the request and for locating the specific filesystem(s) which will
151 service parts of the request. Usually the information in the path
152 assists in locating the correct FS drivers. Sometimes after extensive
153 pre-processing, the VFS starts invoking exported routines in the FS
154 driver. This is the point where the FS specific processing of the
155 request starts, and here the Coda specific kernel code comes into
156 play.
157
158 The FS layer for Coda must expose and implement several interfaces.
159 First and foremost the VFS must be able to make all necessary calls to
160 the Coda FS layer, so the Coda FS driver must expose the VFS interface
161 as applicable in the operating system. These differ very significantly
162 among operating systems, but share features such as facilities to
163 read/write and create and remove objects. The Coda FS layer services
164 such VFS requests by invoking one or more well defined services
165 offered by the cache manager Venus. When the replies from Venus have
166 come back to the FS driver, servicing of the VFS call continues and
167 finishes with a reply to the kernel's VFS. Finally the VFS layer
168 returns to the process.
169
170 As a result of this design a basic interface exposed by the FS driver
171 must allow Venus to manage message traffic. In particular Venus must
172 be able to retrieve and place messages and to be notified of the
173 arrival of a new message. The notification must be through a mechanism
174 which does not block Venus since Venus must attend to other tasks even
175 when no messages are waiting or being processed.
176
177 **Interfaces of the Coda FS Driver**
178
179 Furthermore the FS layer provides for a special path of communication
180 between a user process and Venus, called the pioctl interface. The
181 pioctl interface is used for Coda specific services, such as
182 requesting detailed information about the persistent cache managed by
183 Venus. Here the involvement of the kernel is minimal. It identifies
184 the calling process and passes the information on to Venus. When
185 Venus replies the response is passed back to the caller in unmodified
186 form.
187
188 Finally Venus allows the kernel FS driver to cache the results from
189 certain services. This is done to avoid excessive context switches
190 and results in an efficient system. However, Venus may acquire
191 information, for example from the network which implies that cached
192 information must be flushed or replaced. Venus then makes a downcall
193 to the Coda FS layer to request flushes or updates in the cache. The
194 kernel FS driver handles such requests synchronously.
195
196 Among these interfaces the VFS interface and the facility to place,
197 receive and be notified of messages are platform specific. We will
198 not go into the calls exported to the VFS layer but we will state the
199 requirements of the message exchange mechanism.
200
201
202 3. The message layer
203 =====================
204
205 At the lowest level the communication between Venus and the FS driver
206 proceeds through messages. The synchronization between processes
207 requesting Coda file service and Venus relies on blocking and waking
208 up processes. The Coda FS driver processes VFS- and pioctl-requests
209 on behalf of a process P, creates messages for Venus, awaits replies
210 and finally returns to the caller. The implementation of the exchange
211 of messages is platform specific, but the semantics have (so far)
212 appeared to be generally applicable. Data buffers are created by the
213 FS Driver in kernel memory on behalf of P and copied to user memory in
214 Venus.
215
216 The FS Driver while servicing P makes upcalls to Venus. Such an
217 upcall is dispatched to Venus by creating a message structure. The
218 structure contains the identification of P, the message sequence
219 number, the size of the request and a pointer to the data in kernel
220 memory for the request. Since the data buffer is re-used to hold the
221 reply from Venus, there is a field for the size of the reply. A flags
222 field is used in the message to precisely record the status of the
223 message. Additional platform dependent structures involve pointers to
224 determine the position of the message on queues and pointers to
225 synchronization objects. In the upcall routine the message structure
226 is filled in, flags are set to 0, and it is placed on the *pending*
227 queue. The routine calling upcall is responsible for allocating the
228 data buffer; its structure will be described in the next section.
229
230 A facility must exist to notify Venus that the message has been
231 created, and implemented using available synchronization objects in
232 the OS. This notification is done in the upcall context of the process
233 P. When the message is on the pending queue, process P cannot proceed
234 in upcall. The (kernel mode) processing of P in the filesystem
235 request routine must be suspended until Venus has replied. Therefore
236 the calling thread in P is blocked in upcall. A pointer in the
237 message structure will locate the synchronization object on which P is
238 sleeping.
239
240 Venus detects the notification that a message has arrived, and the FS
241 driver allow Venus to retrieve the message with a getmsg_from_kernel
242 call. This action finishes in the kernel by putting the message on the
243 queue of processing messages and setting flags to READ. Venus is
244 passed the contents of the data buffer. The getmsg_from_kernel call
245 now returns and Venus processes the request.
246
247 At some later point the FS driver receives a message from Venus,
248 namely when Venus calls sendmsg_to_kernel. At this moment the Coda FS
249 driver looks at the contents of the message and decides if:
250
251
252 * the message is a reply for a suspended thread P. If so it removes
253 the message from the processing queue and marks the message as
254 WRITTEN. Finally, the FS driver unblocks P (still in the kernel
255 mode context of Venus) and the sendmsg_to_kernel call returns to
256 Venus. The process P will be scheduled at some point and continues
257 processing its upcall with the data buffer replaced with the reply
258 from Venus.
259
260 * The message is a ``downcall``. A downcall is a request from Venus to
261 the FS Driver. The FS driver processes the request immediately
262 (usually a cache eviction or replacement) and when it finishes
263 sendmsg_to_kernel returns.
264
265 Now P awakes and continues processing upcall. There are some
266 subtleties to take account of. First P will determine if it was woken
267 up in upcall by a signal from some other source (for example an
268 attempt to terminate P) or as is normally the case by Venus in its
269 sendmsg_to_kernel call. In the normal case, the upcall routine will
270 deallocate the message structure and return. The FS routine can proceed
271 with its processing.
272
273
274 **Sleeping and IPC arrangements**
275
276 In case P is woken up by a signal and not by Venus, it will first look
277 at the flags field. If the message is not yet READ, the process P can
278 handle its signal without notifying Venus. If Venus has READ, and
279 the request should not be processed, P can send Venus a signal message
280 to indicate that it should disregard the previous message. Such
281 signals are put in the queue at the head, and read first by Venus. If
282 the message is already marked as WRITTEN it is too late to stop the
283 processing. The VFS routine will now continue. (-- If a VFS request
284 involves more than one upcall, this can lead to complicated state, an
285 extra field "handle_signals" could be added in the message structure
286 to indicate points of no return have been passed.--)
287
288
289
290 3.1. Implementation details
291 ----------------------------
292
293 The Unix implementation of this mechanism has been through the
294 implementation of a character device associated with Coda. Venus
295 retrieves messages by doing a read on the device, replies are sent
296 with a write and notification is through the select system call on the
297 file descriptor for the device. The process P is kept waiting on an
298 interruptible wait queue object.
299
300 In Windows NT and the DPMI Windows 95 implementation a DeviceIoControl
301 call is used. The DeviceIoControl call is designed to copy buffers
302 from user memory to kernel memory with OPCODES. The sendmsg_to_kernel
303 is issued as a synchronous call, while the getmsg_from_kernel call is
304 asynchronous. Windows EventObjects are used for notification of
305 message arrival. The process P is kept waiting on a KernelEvent
306 object in NT and a semaphore in Windows 95.
307
308
309 4. The interface at the call level
310 ===================================
311
312
313 This section describes the upcalls a Coda FS driver can make to Venus.
314 Each of these upcalls make use of two structures: inputArgs and
315 outputArgs. In pseudo BNF form the structures take the following
316 form::
317
318
319 struct inputArgs {
320 u_long opcode;
321 u_long unique; /* Keep multiple outstanding msgs distinct */
322 u_short pid; /* Common to all */
323 u_short pgid; /* Common to all */
324 struct CodaCred cred; /* Common to all */
325
326 <union "in" of call dependent parts of inputArgs>
327 };
328
329 struct outputArgs {
330 u_long opcode;
331 u_long unique; /* Keep multiple outstanding msgs distinct */
332 u_long result;
333
334 <union "out" of call dependent parts of inputArgs>
335 };
336
337
338
339 Before going on let us elucidate the role of the various fields. The
340 inputArgs start with the opcode which defines the type of service
341 requested from Venus. There are approximately 30 upcalls at present
342 which we will discuss. The unique field labels the inputArg with a
343 unique number which will identify the message uniquely. A process and
344 process group id are passed. Finally the credentials of the caller
345 are included.
346
347 Before delving into the specific calls we need to discuss a variety of
348 data structures shared by the kernel and Venus.
349
350
351
352
353 4.1. Data structures shared by the kernel and Venus
354 ----------------------------------------------------
355
356
357 The CodaCred structure defines a variety of user and group ids as
358 they are set for the calling process. The vuid_t and vgid_t are 32 bit
359 unsigned integers. It also defines group membership in an array. On
360 Unix the CodaCred has proven sufficient to implement good security
361 semantics for Coda but the structure may have to undergo modification
362 for the Windows environment when these mature::
363
364 struct CodaCred {
365 vuid_t cr_uid, cr_euid, cr_suid, cr_fsuid; /* Real, effective, set, fs uid */
366 vgid_t cr_gid, cr_egid, cr_sgid, cr_fsgid; /* same for groups */
367 vgid_t cr_groups[NGROUPS]; /* Group membership for caller */
368 };
369
370
371 .. Note::
372
373 It is questionable if we need CodaCreds in Venus. Finally Venus
374 doesn't know about groups, although it does create files with the
375 default uid/gid. Perhaps the list of group membership is superfluous.
376
377
378 The next item is the fundamental identifier used to identify Coda
379 files, the ViceFid. A fid of a file uniquely defines a file or
380 directory in the Coda filesystem within a cell [1]_::
381
382 typedef struct ViceFid {
383 VolumeId Volume;
384 VnodeId Vnode;
385 Unique_t Unique;
386 } ViceFid;
387
388 .. [1] A cell is agroup of Coda servers acting under the aegis of a single
389 system control machine or SCM. See the Coda Administration manual
390 for a detailed description of the role of the SCM.
391
392 Each of the constituent fields: VolumeId, VnodeId and Unique_t are
393 unsigned 32 bit integers. We envisage that a further field will need
394 to be prefixed to identify the Coda cell; this will probably take the
395 form of a Ipv6 size IP address naming the Coda cell through DNS.
396
397 The next important structure shared between Venus and the kernel is
398 the attributes of the file. The following structure is used to
399 exchange information. It has room for future extensions such as
400 support for device files (currently not present in Coda)::
401
402
403 struct coda_timespec {
404 int64_t tv_sec; /* seconds */
405 long tv_nsec; /* nanoseconds */
406 };
407
408 struct coda_vattr {
409 enum coda_vtype va_type; /* vnode type (for create) */
410 u_short va_mode; /* files access mode and type */
411 short va_nlink; /* number of references to file */
412 vuid_t va_uid; /* owner user id */
413 vgid_t va_gid; /* owner group id */
414 long va_fsid; /* file system id (dev for now) */
415 long va_fileid; /* file id */
416 u_quad_t va_size; /* file size in bytes */
417 long va_blocksize; /* blocksize preferred for i/o */
418 struct coda_timespec va_atime; /* time of last access */
419 struct coda_timespec va_mtime; /* time of last modification */
420 struct coda_timespec va_ctime; /* time file changed */
421 u_long va_gen; /* generation number of file */
422 u_long va_flags; /* flags defined for file */
423 dev_t va_rdev; /* device special file represents */
424 u_quad_t va_bytes; /* bytes of disk space held by file */
425 u_quad_t va_filerev; /* file modification number */
426 u_int va_vaflags; /* operations flags, see below */
427 long va_spare; /* remain quad aligned */
428 };
429
430
431 4.2. The pioctl interface
432 --------------------------
433
434
435 Coda specific requests can be made by application through the pioctl
436 interface. The pioctl is implemented as an ordinary ioctl on a
437 fictitious file /coda/.CONTROL. The pioctl call opens this file, gets
438 a file handle and makes the ioctl call. Finally it closes the file.
439
440 The kernel involvement in this is limited to providing the facility to
441 open and close and pass the ioctl message and to verify that a path in
442 the pioctl data buffers is a file in a Coda filesystem.
443
444 The kernel is handed a data packet of the form::
445
446 struct {
447 const char *path;
448 struct ViceIoctl vidata;
449 int follow;
450 } data;
451
452
453
454 where::
455
456
457 struct ViceIoctl {
458 caddr_t in, out; /* Data to be transferred in, or out */
459 short in_size; /* Size of input buffer <= 2K */
460 short out_size; /* Maximum size of output buffer, <= 2K */
461 };
462
463
464
465 The path must be a Coda file, otherwise the ioctl upcall will not be
466 made.
467
468 .. Note:: The data structures and code are a mess. We need to clean this up.
469
470
471 **We now proceed to document the individual calls**:
472
473
474 4.3. root
475 ----------
476
477
478 Arguments
479 in
480
481 empty
482
483 out::
484
485 struct cfs_root_out {
486 ViceFid VFid;
487 } cfs_root;
488
489
490
491 Description
492 This call is made to Venus during the initialization of
493 the Coda filesystem. If the result is zero, the cfs_root structure
494 contains the ViceFid of the root of the Coda filesystem. If a non-zero
495 result is generated, its value is a platform dependent error code
496 indicating the difficulty Venus encountered in locating the root of
497 the Coda filesystem.
498
499 4.4. lookup
500 ------------
501
502
503 Summary
504 Find the ViceFid and type of an object in a directory if it exists.
505
506 Arguments
507 in::
508
509 struct cfs_lookup_in {
510 ViceFid VFid;
511 char *name; /* Place holder for data. */
512 } cfs_lookup;
513
514
515
516 out::
517
518 struct cfs_lookup_out {
519 ViceFid VFid;
520 int vtype;
521 } cfs_lookup;
522
523
524
525 Description
526 This call is made to determine the ViceFid and filetype of
527 a directory entry. The directory entry requested carries name 'name'
528 and Venus will search the directory identified by cfs_lookup_in.VFid.
529 The result may indicate that the name does not exist, or that
530 difficulty was encountered in finding it (e.g. due to disconnection).
531 If the result is zero, the field cfs_lookup_out.VFid contains the
532 targets ViceFid and cfs_lookup_out.vtype the coda_vtype giving the
533 type of object the name designates.
534
535 The name of the object is an 8 bit character string of maximum length
536 CFS_MAXNAMLEN, currently set to 256 (including a 0 terminator.)
537
538 It is extremely important to realize that Venus bitwise ors the field
539 cfs_lookup.vtype with CFS_NOCACHE to indicate that the object should
540 not be put in the kernel name cache.
541
542 .. Note::
543
544 The type of the vtype is currently wrong. It should be
545 coda_vtype. Linux does not take note of CFS_NOCACHE. It should.
546
547
548 4.5. getattr
549 -------------
550
551
552 Summary Get the attributes of a file.
553
554 Arguments
555 in::
556
557 struct cfs_getattr_in {
558 ViceFid VFid;
559 struct coda_vattr attr; /* XXXXX */
560 } cfs_getattr;
561
562
563
564 out::
565
566 struct cfs_getattr_out {
567 struct coda_vattr attr;
568 } cfs_getattr;
569
570
571
572 Description
573 This call returns the attributes of the file identified by fid.
574
575 Errors
576 Errors can occur if the object with fid does not exist, is
577 unaccessible or if the caller does not have permission to fetch
578 attributes.
579
580 .. Note::
581
582 Many kernel FS drivers (Linux, NT and Windows 95) need to acquire
583 the attributes as well as the Fid for the instantiation of an internal
584 "inode" or "FileHandle". A significant improvement in performance on
585 such systems could be made by combining the lookup and getattr calls
586 both at the Venus/kernel interaction level and at the RPC level.
587
588 The vattr structure included in the input arguments is superfluous and
589 should be removed.
590
591
592 4.6. setattr
593 -------------
594
595
596 Summary
597 Set the attributes of a file.
598
599 Arguments
600 in::
601
602 struct cfs_setattr_in {
603 ViceFid VFid;
604 struct coda_vattr attr;
605 } cfs_setattr;
606
607
608
609
610 out
611
612 empty
613
614 Description
615 The structure attr is filled with attributes to be changed
616 in BSD style. Attributes not to be changed are set to -1, apart from
617 vtype which is set to VNON. Other are set to the value to be assigned.
618 The only attributes which the FS driver may request to change are the
619 mode, owner, groupid, atime, mtime and ctime. The return value
620 indicates success or failure.
621
622 Errors
623 A variety of errors can occur. The object may not exist, may
624 be inaccessible, or permission may not be granted by Venus.
625
626
627 4.7. access
628 ------------
629
630
631 Arguments
632 in::
633
634 struct cfs_access_in {
635 ViceFid VFid;
636 int flags;
637 } cfs_access;
638
639
640
641 out
642
643 empty
644
645 Description
646 Verify if access to the object identified by VFid for
647 operations described by flags is permitted. The result indicates if
648 access will be granted. It is important to remember that Coda uses
649 ACLs to enforce protection and that ultimately the servers, not the
650 clients enforce the security of the system. The result of this call
651 will depend on whether a token is held by the user.
652
653 Errors
654 The object may not exist, or the ACL describing the protection
655 may not be accessible.
656
657
658 4.8. create
659 ------------
660
661
662 Summary
663 Invoked to create a file
664
665 Arguments
666 in::
667
668 struct cfs_create_in {
669 ViceFid VFid;
670 struct coda_vattr attr;
671 int excl;
672 int mode;
673 char *name; /* Place holder for data. */
674 } cfs_create;
675
676
677
678
679 out::
680
681 struct cfs_create_out {
682 ViceFid VFid;
683 struct coda_vattr attr;
684 } cfs_create;
685
686
687
688 Description
689 This upcall is invoked to request creation of a file.
690 The file will be created in the directory identified by VFid, its name
691 will be name, and the mode will be mode. If excl is set an error will
692 be returned if the file already exists. If the size field in attr is
693 set to zero the file will be truncated. The uid and gid of the file
694 are set by converting the CodaCred to a uid using a macro CRTOUID
695 (this macro is platform dependent). Upon success the VFid and
696 attributes of the file are returned. The Coda FS Driver will normally
697 instantiate a vnode, inode or file handle at kernel level for the new
698 object.
699
700
701 Errors
702 A variety of errors can occur. Permissions may be insufficient.
703 If the object exists and is not a file the error EISDIR is returned
704 under Unix.
705
706 .. Note::
707
708 The packing of parameters is very inefficient and appears to
709 indicate confusion between the system call creat and the VFS operation
710 create. The VFS operation create is only called to create new objects.
711 This create call differs from the Unix one in that it is not invoked
712 to return a file descriptor. The truncate and exclusive options,
713 together with the mode, could simply be part of the mode as it is
714 under Unix. There should be no flags argument; this is used in open
715 (2) to return a file descriptor for READ or WRITE mode.
716
717 The attributes of the directory should be returned too, since the size
718 and mtime changed.
719
720
721 4.9. mkdir
722 -----------
723
724
725 Summary
726 Create a new directory.
727
728 Arguments
729 in::
730
731 struct cfs_mkdir_in {
732 ViceFid VFid;
733 struct coda_vattr attr;
734 char *name; /* Place holder for data. */
735 } cfs_mkdir;
736
737
738
739 out::
740
741 struct cfs_mkdir_out {
742 ViceFid VFid;
743 struct coda_vattr attr;
744 } cfs_mkdir;
745
746
747
748
749 Description
750 This call is similar to create but creates a directory.
751 Only the mode field in the input parameters is used for creation.
752 Upon successful creation, the attr returned contains the attributes of
753 the new directory.
754
755 Errors
756 As for create.
757
758 .. Note::
759
760 The input parameter should be changed to mode instead of
761 attributes.
762
763 The attributes of the parent should be returned since the size and
764 mtime changes.
765
766
767 4.10. link
768 -----------
769
770
771 Summary
772 Create a link to an existing file.
773
774 Arguments
775 in::
776
777 struct cfs_link_in {
778 ViceFid sourceFid; /* cnode to link *to* */
779 ViceFid destFid; /* Directory in which to place link */
780 char *tname; /* Place holder for data. */
781 } cfs_link;
782
783
784
785 out
786
787 empty
788
789 Description
790 This call creates a link to the sourceFid in the directory
791 identified by destFid with name tname. The source must reside in the
792 target's parent, i.e. the source must be have parent destFid, i.e. Coda
793 does not support cross directory hard links. Only the return value is
794 relevant. It indicates success or the type of failure.
795
796 Errors
797 The usual errors can occur.
798
799
800 4.11. symlink
801 --------------
802
803
804 Summary
805 create a symbolic link
806
807 Arguments
808 in::
809
810 struct cfs_symlink_in {
811 ViceFid VFid; /* Directory to put symlink in */
812 char *srcname;
813 struct coda_vattr attr;
814 char *tname;
815 } cfs_symlink;
816
817
818
819 out
820
821 none
822
823 Description
824 Create a symbolic link. The link is to be placed in the
825 directory identified by VFid and named tname. It should point to the
826 pathname srcname. The attributes of the newly created object are to
827 be set to attr.
828
829 .. Note::
830
831 The attributes of the target directory should be returned since
832 its size changed.
833
834
835 4.12. remove
836 -------------
837
838
839 Summary
840 Remove a file
841
842 Arguments
843 in::
844
845 struct cfs_remove_in {
846 ViceFid VFid;
847 char *name; /* Place holder for data. */
848 } cfs_remove;
849
850
851
852 out
853
854 none
855
856 Description
857 Remove file named cfs_remove_in.name in directory
858 identified by VFid.
859
860
861 .. Note::
862
863 The attributes of the directory should be returned since its
864 mtime and size may change.
865
866
867 4.13. rmdir
868 ------------
869
870
871 Summary
872 Remove a directory
873
874 Arguments
875 in::
876
877 struct cfs_rmdir_in {
878 ViceFid VFid;
879 char *name; /* Place holder for data. */
880 } cfs_rmdir;
881
882
883
884 out
885
886 none
887
888 Description
889 Remove the directory with name 'name' from the directory
890 identified by VFid.
891
892 .. Note:: The attributes of the parent directory should be returned since
893 its mtime and size may change.
894
895
896 4.14. readlink
897 ---------------
898
899
900 Summary
901 Read the value of a symbolic link.
902
903 Arguments
904 in::
905
906 struct cfs_readlink_in {
907 ViceFid VFid;
908 } cfs_readlink;
909
910
911
912 out::
913
914 struct cfs_readlink_out {
915 int count;
916 caddr_t data; /* Place holder for data. */
917 } cfs_readlink;
918
919
920
921 Description
922 This routine reads the contents of symbolic link
923 identified by VFid into the buffer data. The buffer data must be able
924 to hold any name up to CFS_MAXNAMLEN (PATH or NAM??).
925
926 Errors
927 No unusual errors.
928
929
930 4.15. open
931 -----------
932
933
934 Summary
935 Open a file.
936
937 Arguments
938 in::
939
940 struct cfs_open_in {
941 ViceFid VFid;
942 int flags;
943 } cfs_open;
944
945
946
947 out::
948
949 struct cfs_open_out {
950 dev_t dev;
951 ino_t inode;
952 } cfs_open;
953
954
955
956 Description
957 This request asks Venus to place the file identified by
958 VFid in its cache and to note that the calling process wishes to open
959 it with flags as in open(2). The return value to the kernel differs
960 for Unix and Windows systems. For Unix systems the Coda FS Driver is
961 informed of the device and inode number of the container file in the
962 fields dev and inode. For Windows the path of the container file is
963 returned to the kernel.
964
965
966 .. Note::
967
968 Currently the cfs_open_out structure is not properly adapted to
969 deal with the Windows case. It might be best to implement two
970 upcalls, one to open aiming at a container file name, the other at a
971 container file inode.
972
973
974 4.16. close
975 ------------
976
977
978 Summary
979 Close a file, update it on the servers.
980
981 Arguments
982 in::
983
984 struct cfs_close_in {
985 ViceFid VFid;
986 int flags;
987 } cfs_close;
988
989
990
991 out
992
993 none
994
995 Description
996 Close the file identified by VFid.
997
998 .. Note::
999
1000 The flags argument is bogus and not used. However, Venus' code
1001 has room to deal with an execp input field, probably this field should
1002 be used to inform Venus that the file was closed but is still memory
1003 mapped for execution. There are comments about fetching versus not
1004 fetching the data in Venus vproc_vfscalls. This seems silly. If a
1005 file is being closed, the data in the container file is to be the new
1006 data. Here again the execp flag might be in play to create confusion:
1007 currently Venus might think a file can be flushed from the cache when
1008 it is still memory mapped. This needs to be understood.
1009
1010
1011 4.17. ioctl
1012 ------------
1013
1014
1015 Summary
1016 Do an ioctl on a file. This includes the pioctl interface.
1017
1018 Arguments
1019 in::
1020
1021 struct cfs_ioctl_in {
1022 ViceFid VFid;
1023 int cmd;
1024 int len;
1025 int rwflag;
1026 char *data; /* Place holder for data. */
1027 } cfs_ioctl;
1028
1029
1030
1031 out::
1032
1033
1034 struct cfs_ioctl_out {
1035 int len;
1036 caddr_t data; /* Place holder for data. */
1037 } cfs_ioctl;
1038
1039
1040
1041 Description
1042 Do an ioctl operation on a file. The command, len and
1043 data arguments are filled as usual. flags is not used by Venus.
1044
1045 .. Note::
1046
1047 Another bogus parameter. flags is not used. What is the
1048 business about PREFETCHING in the Venus code?
1049
1050
1051
1052 4.18. rename
1053 -------------
1054
1055
1056 Summary
1057 Rename a fid.
1058
1059 Arguments
1060 in::
1061
1062 struct cfs_rename_in {
1063 ViceFid sourceFid;
1064 char *srcname;
1065 ViceFid destFid;
1066 char *destname;
1067 } cfs_rename;
1068
1069
1070
1071 out
1072
1073 none
1074
1075 Description
1076 Rename the object with name srcname in directory
1077 sourceFid to destname in destFid. It is important that the names
1078 srcname and destname are 0 terminated strings. Strings in Unix
1079 kernels are not always null terminated.
1080
1081
1082 4.19. readdir
1083 --------------
1084
1085
1086 Summary
1087 Read directory entries.
1088
1089 Arguments
1090 in::
1091
1092 struct cfs_readdir_in {
1093 ViceFid VFid;
1094 int count;
1095 int offset;
1096 } cfs_readdir;
1097
1098
1099
1100
1101 out::
1102
1103 struct cfs_readdir_out {
1104 int size;
1105 caddr_t data; /* Place holder for data. */
1106 } cfs_readdir;
1107
1108
1109
1110 Description
1111 Read directory entries from VFid starting at offset and
1112 read at most count bytes. Returns the data in data and returns
1113 the size in size.
1114
1115
1116 .. Note::
1117
1118 This call is not used. Readdir operations exploit container
1119 files. We will re-evaluate this during the directory revamp which is
1120 about to take place.
1121
1122
1123 4.20. vget
1124 -----------
1125
1126
1127 Summary
1128 instructs Venus to do an FSDB->Get.
1129
1130 Arguments
1131 in::
1132
1133 struct cfs_vget_in {
1134 ViceFid VFid;
1135 } cfs_vget;
1136
1137
1138
1139 out::
1140
1141 struct cfs_vget_out {
1142 ViceFid VFid;
1143 int vtype;
1144 } cfs_vget;
1145
1146
1147
1148 Description
1149 This upcall asks Venus to do a get operation on an fsobj
1150 labelled by VFid.
1151
1152 .. Note::
1153
1154 This operation is not used. However, it is extremely useful
1155 since it can be used to deal with read/write memory mapped files.
1156 These can be "pinned" in the Venus cache using vget and released with
1157 inactive.
1158
1159
1160 4.21. fsync
1161 ------------
1162
1163
1164 Summary
1165 Tell Venus to update the RVM attributes of a file.
1166
1167 Arguments
1168 in::
1169
1170 struct cfs_fsync_in {
1171 ViceFid VFid;
1172 } cfs_fsync;
1173
1174
1175
1176 out
1177
1178 none
1179
1180 Description
1181 Ask Venus to update RVM attributes of object VFid. This
1182 should be called as part of kernel level fsync type calls. The
1183 result indicates if the syncing was successful.
1184
1185 .. Note:: Linux does not implement this call. It should.
1186
1187
1188 4.22. inactive
1189 ---------------
1190
1191
1192 Summary
1193 Tell Venus a vnode is no longer in use.
1194
1195 Arguments
1196 in::
1197
1198 struct cfs_inactive_in {
1199 ViceFid VFid;
1200 } cfs_inactive;
1201
1202
1203
1204 out
1205
1206 none
1207
1208 Description
1209 This operation returns EOPNOTSUPP.
1210
1211 .. Note:: This should perhaps be removed.
1212
1213
1214 4.23. rdwr
1215 -----------
1216
1217
1218 Summary
1219 Read or write from a file
1220
1221 Arguments
1222 in::
1223
1224 struct cfs_rdwr_in {
1225 ViceFid VFid;
1226 int rwflag;
1227 int count;
1228 int offset;
1229 int ioflag;
1230 caddr_t data; /* Place holder for data. */
1231 } cfs_rdwr;
1232
1233
1234
1235
1236 out::
1237
1238 struct cfs_rdwr_out {
1239 int rwflag;
1240 int count;
1241 caddr_t data; /* Place holder for data. */
1242 } cfs_rdwr;
1243
1244
1245
1246 Description
1247 This upcall asks Venus to read or write from a file.
1248
1249
1250 .. Note::
1251
1252 It should be removed since it is against the Coda philosophy that
1253 read/write operations never reach Venus. I have been told the
1254 operation does not work. It is not currently used.
1255
1256
1257
1258 4.24. odymount
1259 ---------------
1260
1261
1262 Summary
1263 Allows mounting multiple Coda "filesystems" on one Unix mount point.
1264
1265 Arguments
1266 in::
1267
1268 struct ody_mount_in {
1269 char *name; /* Place holder for data. */
1270 } ody_mount;
1271
1272
1273
1274 out::
1275
1276 struct ody_mount_out {
1277 ViceFid VFid;
1278 } ody_mount;
1279
1280
1281
1282 Description
1283 Asks Venus to return the rootfid of a Coda system named
1284 name. The fid is returned in VFid.
1285
1286 .. Note::
1287
1288 This call was used by David for dynamic sets. It should be
1289 removed since it causes a jungle of pointers in the VFS mounting area.
1290 It is not used by Coda proper. Call is not implemented by Venus.
1291
1292
1293 4.25. ody_lookup
1294 -----------------
1295
1296
1297 Summary
1298 Looks up something.
1299
1300 Arguments
1301 in
1302
1303 irrelevant
1304
1305
1306 out
1307
1308 irrelevant
1309
1310
1311 .. Note:: Gut it. Call is not implemented by Venus.
1312
1313
1314 4.26. ody_expand
1315 -----------------
1316
1317
1318 Summary
1319 expands something in a dynamic set.
1320
1321 Arguments
1322 in
1323
1324 irrelevant
1325
1326 out
1327
1328 irrelevant
1329
1330 .. Note:: Gut it. Call is not implemented by Venus.
1331
1332
1333 4.27. prefetch
1334 ---------------
1335
1336
1337 Summary
1338 Prefetch a dynamic set.
1339
1340 Arguments
1341
1342 in
1343
1344 Not documented.
1345
1346 out
1347
1348 Not documented.
1349
1350 Description
1351 Venus worker.cc has support for this call, although it is
1352 noted that it doesn't work. Not surprising, since the kernel does not
1353 have support for it. (ODY_PREFETCH is not a defined operation).
1354
1355
1356 .. Note:: Gut it. It isn't working and isn't used by Coda.
1357
1358
1359
1360 4.28. signal
1361 -------------
1362
1363
1364 Summary
1365 Send Venus a signal about an upcall.
1366
1367 Arguments
1368 in
1369
1370 none
1371
1372 out
1373
1374 not applicable.
1375
1376 Description
1377 This is an out-of-band upcall to Venus to inform Venus
1378 that the calling process received a signal after Venus read the
1379 message from the input queue. Venus is supposed to clean up the
1380 operation.
1381
1382 Errors
1383 No reply is given.
1384
1385 .. Note::
1386
1387 We need to better understand what Venus needs to clean up and if
1388 it is doing this correctly. Also we need to handle multiple upcall
1389 per system call situations correctly. It would be important to know
1390 what state changes in Venus take place after an upcall for which the
1391 kernel is responsible for notifying Venus to clean up (e.g. open
1392 definitely is such a state change, but many others are maybe not).
1393
1394
1395 5. The minicache and downcalls
1396 ===============================
1397
1398
1399 The Coda FS Driver can cache results of lookup and access upcalls, to
1400 limit the frequency of upcalls. Upcalls carry a price since a process
1401 context switch needs to take place. The counterpart of caching the
1402 information is that Venus will notify the FS Driver that cached
1403 entries must be flushed or renamed.
1404
1405 The kernel code generally has to maintain a structure which links the
1406 internal file handles (called vnodes in BSD, inodes in Linux and
1407 FileHandles in Windows) with the ViceFid's which Venus maintains. The
1408 reason is that frequent translations back and forth are needed in
1409 order to make upcalls and use the results of upcalls. Such linking
1410 objects are called cnodes.
1411
1412 The current minicache implementations have cache entries which record
1413 the following:
1414
1415 1. the name of the file
1416
1417 2. the cnode of the directory containing the object
1418
1419 3. a list of CodaCred's for which the lookup is permitted.
1420
1421 4. the cnode of the object
1422
1423 The lookup call in the Coda FS Driver may request the cnode of the
1424 desired object from the cache, by passing its name, directory and the
1425 CodaCred's of the caller. The cache will return the cnode or indicate
1426 that it cannot be found. The Coda FS Driver must be careful to
1427 invalidate cache entries when it modifies or removes objects.
1428
1429 When Venus obtains information that indicates that cache entries are
1430 no longer valid, it will make a downcall to the kernel. Downcalls are
1431 intercepted by the Coda FS Driver and lead to cache invalidations of
1432 the kind described below. The Coda FS Driver does not return an error
1433 unless the downcall data could not be read into kernel memory.
1434
1435
1436 5.1. INVALIDATE
1437 ----------------
1438
1439
1440 No information is available on this call.
1441
1442
1443 5.2. FLUSH
1444 -----------
1445
1446
1447
1448 Arguments
1449 None
1450
1451 Summary
1452 Flush the name cache entirely.
1453
1454 Description
1455 Venus issues this call upon startup and when it dies. This
1456 is to prevent stale cache information being held. Some operating
1457 systems allow the kernel name cache to be switched off dynamically.
1458 When this is done, this downcall is made.
1459
1460
1461 5.3. PURGEUSER
1462 ---------------
1463
1464
1465 Arguments
1466 ::
1467
1468 struct cfs_purgeuser_out {/* CFS_PURGEUSER is a venus->kernel call */
1469 struct CodaCred cred;
1470 } cfs_purgeuser;
1471
1472
1473
1474 Description
1475 Remove all entries in the cache carrying the Cred. This
1476 call is issued when tokens for a user expire or are flushed.
1477
1478
1479 5.4. ZAPFILE
1480 -------------
1481
1482
1483 Arguments
1484 ::
1485
1486 struct cfs_zapfile_out { /* CFS_ZAPFILE is a venus->kernel call */
1487 ViceFid CodaFid;
1488 } cfs_zapfile;
1489
1490
1491
1492 Description
1493 Remove all entries which have the (dir vnode, name) pair.
1494 This is issued as a result of an invalidation of cached attributes of
1495 a vnode.
1496
1497 .. Note::
1498
1499 Call is not named correctly in NetBSD and Mach. The minicache
1500 zapfile routine takes different arguments. Linux does not implement
1501 the invalidation of attributes correctly.
1502
1503
1504
1505 5.5. ZAPDIR
1506 ------------
1507
1508
1509 Arguments
1510 ::
1511
1512 struct cfs_zapdir_out { /* CFS_ZAPDIR is a venus->kernel call */
1513 ViceFid CodaFid;
1514 } cfs_zapdir;
1515
1516
1517
1518 Description
1519 Remove all entries in the cache lying in a directory
1520 CodaFid, and all children of this directory. This call is issued when
1521 Venus receives a callback on the directory.
1522
1523
1524 5.6. ZAPVNODE
1525 --------------
1526
1527
1528
1529 Arguments
1530 ::
1531
1532 struct cfs_zapvnode_out { /* CFS_ZAPVNODE is a venus->kernel call */
1533 struct CodaCred cred;
1534 ViceFid VFid;
1535 } cfs_zapvnode;
1536
1537
1538
1539 Description
1540 Remove all entries in the cache carrying the cred and VFid
1541 as in the arguments. This downcall is probably never issued.
1542
1543
1544 5.7. PURGEFID
1545 --------------
1546
1547
1548 Arguments
1549 ::
1550
1551 struct cfs_purgefid_out { /* CFS_PURGEFID is a venus->kernel call */
1552 ViceFid CodaFid;
1553 } cfs_purgefid;
1554
1555
1556
1557 Description
1558 Flush the attribute for the file. If it is a dir (odd
1559 vnode), purge its children from the namecache and remove the file from the
1560 namecache.
1561
1562
1563
1564 5.8. REPLACE
1565 -------------
1566
1567
1568 Summary
1569 Replace the Fid's for a collection of names.
1570
1571 Arguments
1572 ::
1573
1574 struct cfs_replace_out { /* cfs_replace is a venus->kernel call */
1575 ViceFid NewFid;
1576 ViceFid OldFid;
1577 } cfs_replace;
1578
1579
1580
1581 Description
1582 This routine replaces a ViceFid in the name cache with
1583 another. It is added to allow Venus during reintegration to replace
1584 locally allocated temp fids while disconnected with global fids even
1585 when the reference counts on those fids are not zero.
1586
1587
1588 6. Initialization and cleanup
1589 ==============================
1590
1591
1592 This section gives brief hints as to desirable features for the Coda
1593 FS Driver at startup and upon shutdown or Venus failures. Before
1594 entering the discussion it is useful to repeat that the Coda FS Driver
1595 maintains the following data:
1596
1597
1598 1. message queues
1599
1600 2. cnodes
1601
1602 3. name cache entries
1603
1604 The name cache entries are entirely private to the driver, so they
1605 can easily be manipulated. The message queues will generally have
1606 clear points of initialization and destruction. The cnodes are
1607 much more delicate. User processes hold reference counts in Coda
1608 filesystems and it can be difficult to clean up the cnodes.
1609
1610 It can expect requests through:
1611
1612 1. the message subsystem
1613
1614 2. the VFS layer
1615
1616 3. pioctl interface
1617
1618 Currently the pioctl passes through the VFS for Coda so we can
1619 treat these similarly.
1620
1621
1622 6.1. Requirements
1623 ------------------
1624
1625
1626 The following requirements should be accommodated:
1627
1628 1. The message queues should have open and close routines. On Unix
1629 the opening of the character devices are such routines.
1630
1631 - Before opening, no messages can be placed.
1632
1633 - Opening will remove any old messages still pending.
1634
1635 - Close will notify any sleeping processes that their upcall cannot
1636 be completed.
1637
1638 - Close will free all memory allocated by the message queues.
1639
1640
1641 2. At open the namecache shall be initialized to empty state.
1642
1643 3. Before the message queues are open, all VFS operations will fail.
1644 Fortunately this can be achieved by making sure than mounting the
1645 Coda filesystem cannot succeed before opening.
1646
1647 4. After closing of the queues, no VFS operations can succeed. Here
1648 one needs to be careful, since a few operations (lookup,
1649 read/write, readdir) can proceed without upcalls. These must be
1650 explicitly blocked.
1651
1652 5. Upon closing the namecache shall be flushed and disabled.
1653
1654 6. All memory held by cnodes can be freed without relying on upcalls.
1655
1656 7. Unmounting the file system can be done without relying on upcalls.
1657
1658 8. Mounting the Coda filesystem should fail gracefully if Venus cannot
1659 get the rootfid or the attributes of the rootfid. The latter is
1660 best implemented by Venus fetching these objects before attempting
1661 to mount.
1662
1663 .. Note::
1664
1665 NetBSD in particular but also Linux have not implemented the
1666 above requirements fully. For smooth operation this needs to be
1667 corrected.
1668
1669
1670
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.