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Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Apr 15 15:18:58 2008 +0100 (2008-04-15)
parents 831230e53067
line source
2 This is one of the technical documents describing a component of
3 Coda -- this document describes the client kernel-Venus interface.
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
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.
15 The server needs a user level server and at present does not depend on
16 kernel support.
24 The Venus kernel interface
25 Peter J. Braam
26 v1.0, Nov 9, 1997
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 ______________________________________________________________________
34 Table of Contents
90 1. Introduction
92 2. Servicing Coda filesystem calls
94 3. The message layer
96 3.1 Implementation details
98 4. The interface at the call level
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
129 5. The minicache and downcalls
132 5.2 FLUSH
134 5.4 ZAPFILE
135 5.5 ZAPDIR
136 5.6 ZAPVNODE
137 5.7 PURGEFID
138 5.8 REPLACE
140 6. Initialization and cleanup
142 6.1 Requirements
145 ______________________________________________________________________
146 0wpage
148 11.. IInnttrroodduuccttiioonn
152 A key component in the Coda Distributed File System is the cache
153 manager, _V_e_n_u_s.
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.
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.
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.
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.
192 0wpage
194 22.. SSeerrvviicciinngg CCooddaa ffiilleessyysstteemm ccaallllss
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_, .
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.
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.
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.
238 Interfaces of the Coda FS Driver
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.
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.
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.
262 0wpage
264 33.. TThhee mmeessssaaggee llaayyeerr
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.
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.
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.
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.
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:
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.
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.
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.
342 Sleeping and IPC arrangements
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.--)
358 33..11.. IImmpplleemmeennttaattiioonn ddeettaaiillss
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.
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.
375 0wpage
377 44.. TThhee iinntteerrffaaccee aatt tthhee ccaallll lleevveell
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:
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 */
393 <union "in" of call dependent parts of inputArgs>
394 };
396 struct outputArgs {
397 u_long opcode;
398 u_long unique; /* Keep multiple outstanding msgs distinct */
399 u_long result;
401 <union "out" of call dependent parts of inputArgs>
402 };
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.
414 Before delving into the specific calls we need to discuss a variety of
415 data structures shared by the kernel and Venus.
420 44..11.. DDaattaa ssttrruuccttuurreess sshhaarreedd bbyy tthhee kkeerrnneell aanndd VVeennuuss
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.
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 };
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.
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.--)
451 typedef struct ViceFid {
452 VolumeId Volume;
453 VnodeId Vnode;
454 Unique_t Unique;
455 } ViceFid;
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.
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).
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 };
511 44..22.. TThhee ppiiooccttll iinntteerrffaaccee
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.
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.
523 The kernel is handed a data packet of the form:
525 struct {
526 const char *path;
527 struct ViceIoctl vidata;
528 int follow;
529 } data;
533 where
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 };
544 The path must be a Coda file, otherwise the ioctl upcall will not be
545 made.
547 NNOOTTEE The data structures and code are a mess. We need to clean this
548 up.
550 We now proceed to document the individual calls:
552 0wpage
554 44..33.. rroooott
557 AArrgguummeennttss
559 iinn empty
561 oouutt
563 struct cfs_root_out {
564 ViceFid VFid;
565 } cfs_root;
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.
576 0wpage
578 44..44.. llooookkuupp
581 SSuummmmaarryy Find the ViceFid and type of an object in a directory if it
582 exists.
584 AArrgguummeennttss
586 iinn
588 struct cfs_lookup_in {
589 ViceFid VFid;
590 char *name; /* Place holder for data. */
591 } cfs_lookup;
595 oouutt
597 struct cfs_lookup_out {
598 ViceFid VFid;
599 int vtype;
600 } cfs_lookup;
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.
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.)
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.
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.
623 0wpage
625 44..55.. ggeettaattttrr
628 SSuummmmaarryy Get the attributes of a file.
630 AArrgguummeennttss
632 iinn
634 struct cfs_getattr_in {
635 ViceFid VFid;
636 struct coda_vattr attr; /* XXXXX */
637 } cfs_getattr;
641 oouutt
643 struct cfs_getattr_out {
644 struct coda_vattr attr;
645 } cfs_getattr;
649 DDeessccrriippttiioonn This call returns the attributes of the file identified by
650 fid.
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.
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.
662 The vattr structure included in the input arguments is superfluous and
663 should be removed.
665 0wpage
667 44..66.. sseettaattttrr
670 SSuummmmaarryy Set the attributes of a file.
672 AArrgguummeennttss
674 iinn
676 struct cfs_setattr_in {
677 ViceFid VFid;
678 struct coda_vattr attr;
679 } cfs_setattr;
684 oouutt
685 empty
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.
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.
697 0wpage
699 44..77.. aacccceessss
702 SSuummmmaarryy
704 AArrgguummeennttss
706 iinn
708 struct cfs_access_in {
709 ViceFid VFid;
710 int flags;
711 } cfs_access;
715 oouutt
716 empty
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.
725 EErrrroorrss The object may not exist, or the ACL describing the protection
726 may not be accessible.
728 0wpage
730 44..88.. ccrreeaattee
733 SSuummmmaarryy Invoked to create a file
735 AArrgguummeennttss
737 iinn
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;
750 oouutt
752 struct cfs_create_out {
753 ViceFid VFid;
754 struct coda_vattr attr;
755 } cfs_create;
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.
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.
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.
784 The attributes of the directory should be returned too, since the size
785 and mtime changed.
787 0wpage
789 44..99.. mmkkddiirr
792 SSuummmmaarryy Create a new directory.
794 AArrgguummeennttss
796 iinn
798 struct cfs_mkdir_in {
799 ViceFid VFid;
800 struct coda_vattr attr;
801 char *name; /* Place holder for data. */
802 } cfs_mkdir;
806 oouutt
808 struct cfs_mkdir_out {
809 ViceFid VFid;
810 struct coda_vattr attr;
811 } cfs_mkdir;
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.
821 EErrrroorrss As for create.
823 NNOOTTEE The input parameter should be changed to mode instead of
824 attributes.
826 The attributes of the parent should be returned since the size and
827 mtime changes.
829 0wpage
831 44..1100.. lliinnkk
834 SSuummmmaarryy Create a link to an existing file.
836 AArrgguummeennttss
838 iinn
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;
848 oouutt
849 empty
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.
857 EErrrroorrss The usual errors can occur.0wpage
859 44..1111.. ssyymmlliinnkk
862 SSuummmmaarryy create a symbolic link
864 AArrgguummeennttss
866 iinn
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;
877 oouutt
878 none
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.
885 EErrrroorrss
887 NNOOTTEE The attributes of the target directory should be returned since
888 its size changed.
890 0wpage
892 44..1122.. rreemmoovvee
895 SSuummmmaarryy Remove a file
897 AArrgguummeennttss
899 iinn
901 struct cfs_remove_in {
902 ViceFid VFid;
903 char *name; /* Place holder for data. */
904 } cfs_remove;
908 oouutt
909 none
911 DDeessccrriippttiioonn Remove file named cfs_remove_in.name in directory
912 identified by VFid.
914 EErrrroorrss
916 NNOOTTEE The attributes of the directory should be returned since its
917 mtime and size may change.
919 0wpage
921 44..1133.. rrmmddiirr
924 SSuummmmaarryy Remove a directory
926 AArrgguummeennttss
928 iinn
930 struct cfs_rmdir_in {
931 ViceFid VFid;
932 char *name; /* Place holder for data. */
933 } cfs_rmdir;
937 oouutt
938 none
940 DDeessccrriippttiioonn Remove the directory with name name from the directory
941 identified by VFid.
943 EErrrroorrss
945 NNOOTTEE The attributes of the parent directory should be returned since
946 its mtime and size may change.
948 0wpage
950 44..1144.. rreeaaddlliinnkk
953 SSuummmmaarryy Read the value of a symbolic link.
955 AArrgguummeennttss
957 iinn
959 struct cfs_readlink_in {
960 ViceFid VFid;
961 } cfs_readlink;
965 oouutt
967 struct cfs_readlink_out {
968 int count;
969 caddr_t data; /* Place holder for data. */
970 } cfs_readlink;
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??).
978 EErrrroorrss No unusual errors.
980 0wpage
982 44..1155.. ooppeenn
985 SSuummmmaarryy Open a file.
987 AArrgguummeennttss
989 iinn
991 struct cfs_open_in {
992 ViceFid VFid;
993 int flags;
994 } cfs_open;
998 oouutt
1000 struct cfs_open_out {
1001 dev_t dev;
1002 ino_t inode;
1003 } cfs_open;
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
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.
1021 0wpage
1023 44..1166.. cclloossee
1026 SSuummmmaarryy Close a file, update it on the servers.
1028 AArrgguummeennttss
1030 iinn
1032 struct cfs_close_in {
1033 ViceFid VFid;
1034 int flags;
1035 } cfs_close;
1039 oouutt
1040 none
1042 DDeessccrriippttiioonn Close the file identified by VFid.
1044 EErrrroorrss
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.
1056 0wpage
1058 44..1177.. iiooccttll
1061 SSuummmmaarryy Do an ioctl on a file. This includes the pioctl interface.
1063 AArrgguummeennttss
1065 iinn
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;
1077 oouutt
1080 struct cfs_ioctl_out {
1081 int len;
1082 caddr_t data; /* Place holder for data. */
1083 } cfs_ioctl;
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.
1090 EErrrroorrss
1092 NNOOTTEE Another bogus parameter. flags is not used. What is the
1093 business about PREFETCHING in the Venus code?
1096 0wpage
1098 44..1188.. rreennaammee
1101 SSuummmmaarryy Rename a fid.
1103 AArrgguummeennttss
1105 iinn
1107 struct cfs_rename_in {
1108 ViceFid sourceFid;
1109 char *srcname;
1110 ViceFid destFid;
1111 char *destname;
1112 } cfs_rename;
1116 oouutt
1117 none
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.
1124 EErrrroorrss
1126 0wpage
1128 44..1199.. rreeaaddddiirr
1131 SSuummmmaarryy Read directory entries.
1133 AArrgguummeennttss
1135 iinn
1137 struct cfs_readdir_in {
1138 ViceFid VFid;
1139 int count;
1140 int offset;
1141 } cfs_readdir;
1146 oouutt
1148 struct cfs_readdir_out {
1149 int size;
1150 caddr_t data; /* Place holder for data. */
1151 } cfs_readdir;
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.
1159 EErrrroorrss
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.
1165 0wpage
1167 44..2200.. vvggeett
1170 SSuummmmaarryy instructs Venus to do an FSDB->Get.
1172 AArrgguummeennttss
1174 iinn
1176 struct cfs_vget_in {
1177 ViceFid VFid;
1178 } cfs_vget;
1182 oouutt
1184 struct cfs_vget_out {
1185 ViceFid VFid;
1186 int vtype;
1187 } cfs_vget;
1191 DDeessccrriippttiioonn This upcall asks Venus to do a get operation on an fsobj
1192 labelled by VFid.
1194 EErrrroorrss
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.
1201 0wpage
1203 44..2211.. ffssyynncc
1206 SSuummmmaarryy Tell Venus to update the RVM attributes of a file.
1208 AArrgguummeennttss
1210 iinn
1212 struct cfs_fsync_in {
1213 ViceFid VFid;
1214 } cfs_fsync;
1218 oouutt
1219 none
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.
1225 EErrrroorrss
1227 NNOOTTEE Linux does not implement this call. It should.
1229 0wpage
1231 44..2222.. iinnaaccttiivvee
1234 SSuummmmaarryy Tell Venus a vnode is no longer in use.
1236 AArrgguummeennttss
1238 iinn
1240 struct cfs_inactive_in {
1241 ViceFid VFid;
1242 } cfs_inactive;
1246 oouutt
1247 none
1249 DDeessccrriippttiioonn This operation returns EOPNOTSUPP.
1251 EErrrroorrss
1253 NNOOTTEE This should perhaps be removed.
1255 0wpage
1257 44..2233.. rrddwwrr
1260 SSuummmmaarryy Read or write from a file
1262 AArrgguummeennttss
1264 iinn
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;
1278 oouutt
1280 struct cfs_rdwr_out {
1281 int rwflag;
1282 int count;
1283 caddr_t data; /* Place holder for data. */
1284 } cfs_rdwr;
1288 DDeessccrriippttiioonn This upcall asks Venus to read or write from a file.
1290 EErrrroorrss
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.
1297 0wpage
1299 44..2244.. ooddyymmoouunntt
1302 SSuummmmaarryy Allows mounting multiple Coda "filesystems" on one Unix mount
1303 point.
1305 AArrgguummeennttss
1307 iinn
1309 struct ody_mount_in {
1310 char *name; /* Place holder for data. */
1311 } ody_mount;
1315 oouutt
1317 struct ody_mount_out {
1318 ViceFid VFid;
1319 } ody_mount;
1323 DDeessccrriippttiioonn Asks Venus to return the rootfid of a Coda system named
1324 name. The fid is returned in VFid.
1326 EErrrroorrss
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.
1332 0wpage
1334 44..2255.. ooddyy__llooookkuupp
1337 SSuummmmaarryy Looks up something.
1339 AArrgguummeennttss
1341 iinn irrelevant
1344 oouutt
1345 irrelevant
1347 DDeessccrriippttiioonn
1349 EErrrroorrss
1351 NNOOTTEE Gut it. Call is not implemented by Venus.
1353 0wpage
1355 44..2266.. ooddyy__eexxppaanndd
1358 SSuummmmaarryy expands something in a dynamic set.
1360 AArrgguummeennttss
1362 iinn irrelevant
1364 oouutt
1365 irrelevant
1367 DDeessccrriippttiioonn
1369 EErrrroorrss
1371 NNOOTTEE Gut it. Call is not implemented by Venus.
1373 0wpage
1375 44..2277.. pprreeffeettcchh
1378 SSuummmmaarryy Prefetch a dynamic set.
1380 AArrgguummeennttss
1382 iinn Not documented.
1384 oouutt
1385 Not documented.
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).
1391 EErrrroorrss
1393 NNOOTTEE Gut it. It isn't working and isn't used by Coda.
1396 0wpage
1398 44..2288.. ssiiggnnaall
1401 SSuummmmaarryy Send Venus a signal about an upcall.
1403 AArrgguummeennttss
1405 iinn none
1407 oouutt
1408 not applicable.
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.
1415 EErrrroorrss No reply is given.
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).
1424 0wpage
1426 55.. TThhee mmiinniiccaacchhee aanndd ddoowwnnccaallllss
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.
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.
1442 The current minicache implementations have cache entries which record
1443 the following:
1445 1. the name of the file
1447 2. the cnode of the directory containing the object
1449 3. a list of CodaCred's for which the lookup is permitted.
1451 4. the cnode of the object
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.
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.
1469 No information is available on this call.
1472 55..22.. FFLLUUSSHH
1476 AArrgguummeennttss None
1478 SSuummmmaarryy Flush the name cache entirely.
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.
1489 AArrgguummeennttss
1491 struct cfs_purgeuser_out {/* CFS_PURGEUSER is a venus->kernel call */
1492 struct CodaCred cred;
1493 } cfs_purgeuser;
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.
1501 55..44.. ZZAAPPFFIILLEE
1504 AArrgguummeennttss
1506 struct cfs_zapfile_out { /* CFS_ZAPFILE is a venus->kernel call */
1507 ViceFid CodaFid;
1508 } cfs_zapfile;
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.
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.
1522 55..55.. ZZAAPPDDIIRR
1525 AArrgguummeennttss
1527 struct cfs_zapdir_out { /* CFS_ZAPDIR is a venus->kernel call */
1528 ViceFid CodaFid;
1529 } cfs_zapdir;
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.
1542 AArrgguummeennttss
1544 struct cfs_zapvnode_out { /* CFS_ZAPVNODE is a venus->kernel call */
1545 struct CodaCred cred;
1546 ViceFid VFid;
1547 } cfs_zapvnode;
1551 DDeessccrriippttiioonn Remove all entries in the cache carrying the cred and VFid
1552 as in the arguments. This downcall is probably never issued.
1558 SSuummmmaarryy
1560 AArrgguummeennttss
1562 struct cfs_purgefid_out { /* CFS_PURGEFID is a venus->kernel call */
1563 ViceFid CodaFid;
1564 } cfs_purgefid;
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.
1574 55..88.. RREEPPLLAACCEE
1577 SSuummmmaarryy Replace the Fid's for a collection of names.
1579 AArrgguummeennttss
1581 struct cfs_replace_out { /* cfs_replace is a venus->kernel call */
1582 ViceFid NewFid;
1583 ViceFid OldFid;
1584 } cfs_replace;
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.
1593 0wpage
1595 66.. IInniittiiaalliizzaattiioonn aanndd cclleeaannuupp
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:
1604 1. message queues
1606 2. cnodes
1608 3. name cache entries
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.
1616 It can expect requests through:
1618 1. the message subsystem
1620 2. the VFS layer
1622 3. pioctl interface
1624 Currently the _p_i_o_c_t_l passes through the VFS for Coda so we can
1625 treat these similarly.
1628 66..11.. RReeqquuiirreemmeennttss
1631 The following requirements should be accommodated:
1633 1. The message queues should have open and close routines. On Unix
1634 the opening of the character devices are such routines.
1636 +o Before opening, no messages can be placed.
1638 +o Opening will remove any old messages still pending.
1640 +o Close will notify any sleeping processes that their upcall cannot
1641 be completed.
1643 +o Close will free all memory allocated by the message queues.
1646 2. At open the namecache shall be initialized to empty state.
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.
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.
1657 5. Upon closing the namecache shall be flushed and disabled.
1659 6. All memory held by cnodes can be freed without relying on upcalls.
1661 7. Unmounting the file system can be done without relying on upcalls.
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.
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.