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