mount.h revision 10431
1/* 2 * Copyright (c) 1989, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)mount.h 8.13 (Berkeley) 3/27/94 34 * $Id: mount.h,v 1.25 1995/08/28 09:19:05 julian Exp $ 35 */ 36 37#ifndef _SYS_MOUNT_H_ 38#define _SYS_MOUNT_H_ 39 40#ifndef KERNEL 41#include <sys/ucred.h> 42#endif 43#include <sys/queue.h> 44 45typedef struct { long val[2]; } fsid_t; /* file system id type */ 46 47/* 48 * File identifier. 49 * These are unique per filesystem on a single machine. 50 */ 51#define MAXFIDSZ 16 52 53struct fid { 54 u_short fid_len; /* length of data in bytes */ 55 u_short fid_reserved; /* force longword alignment */ 56 char fid_data[MAXFIDSZ]; /* data (variable length) */ 57}; 58 59/* 60 * file system statistics 61 */ 62 63#define MNAMELEN 90 /* length of buffer for returned name */ 64 65struct statfs { 66 short f_type; /* type of filesystem (see below) */ 67 short f_flags; /* copy of mount flags */ 68 long f_bsize; /* fundamental file system block size */ 69 long f_iosize; /* optimal transfer block size */ 70 long f_blocks; /* total data blocks in file system */ 71 long f_bfree; /* free blocks in fs */ 72 long f_bavail; /* free blocks avail to non-superuser */ 73 long f_files; /* total file nodes in file system */ 74 long f_ffree; /* free file nodes in fs */ 75 fsid_t f_fsid; /* file system id */ 76 long f_spare[9]; /* spare for later */ 77 char f_mntonname[MNAMELEN]; /* directory on which mounted */ 78 char f_mntfromname[MNAMELEN];/* mounted filesystem */ 79}; 80 81/* 82 * File system types. 83 */ 84#define MOUNT_NONE 0 85#define MOUNT_UFS 1 /* Fast Filesystem */ 86#define MOUNT_NFS 2 /* Sun-compatible Network Filesystem */ 87#define MOUNT_MFS 3 /* Memory-based Filesystem */ 88#define MOUNT_MSDOS 4 /* MS/DOS Filesystem */ 89#define MOUNT_LFS 5 /* Log-based Filesystem */ 90#define MOUNT_LOFS 6 /* Loopback Filesystem */ 91#define MOUNT_FDESC 7 /* File Descriptor Filesystem */ 92#define MOUNT_PORTAL 8 /* Portal Filesystem */ 93#define MOUNT_NULL 9 /* Minimal Filesystem Layer */ 94#define MOUNT_UMAP 10 /* User/Group Identifer Remapping Filesystem */ 95#define MOUNT_KERNFS 11 /* Kernel Information Filesystem */ 96#define MOUNT_PROCFS 12 /* /proc Filesystem */ 97#define MOUNT_AFS 13 /* Andrew Filesystem */ 98#define MOUNT_CD9660 14 /* ISO9660 (aka CDROM) Filesystem */ 99#define MOUNT_UNION 15 /* Union (translucent) Filesystem */ 100#define MOUNT_DEVFS 16 /* existing device Filesystem */ 101#define MOUNT_MAXTYPE 16 102 103#define INITMOUNTNAMES { \ 104 "none", /* 0 MOUNT_NONE */ \ 105 "ufs", /* 1 MOUNT_UFS */ \ 106 "nfs", /* 2 MOUNT_NFS */ \ 107 "mfs", /* 3 MOUNT_MFS */ \ 108 "msdos", /* 4 MOUNT_MSDOS */ \ 109 "lfs", /* 5 MOUNT_LFS */ \ 110 "lofs", /* 6 MOUNT_LOFS */ \ 111 "fdesc", /* 7 MOUNT_FDESC */ \ 112 "portal", /* 8 MOUNT_PORTAL */ \ 113 "null", /* 9 MOUNT_NULL */ \ 114 "umap", /* 10 MOUNT_UMAP */ \ 115 "kernfs", /* 11 MOUNT_KERNFS */ \ 116 "procfs", /* 12 MOUNT_PROCFS */ \ 117 "afs", /* 13 MOUNT_AFS */ \ 118 "cd9660", /* 14 MOUNT_CD9660 */ \ 119 "union", /* 15 MOUNT_UNION */ \ 120 "devfs", /* 15 MOUNT_DEVFS */ \ 121 0, /* 16 MOUNT_SPARE */ \ 122} 123 124/* 125 * Structure per mounted file system. Each mounted file system has an 126 * array of operations and an instance record. The file systems are 127 * put on a doubly linked list. 128 */ 129LIST_HEAD(vnodelst, vnode); 130 131struct mount { 132 CIRCLEQ_ENTRY(mount) mnt_list; /* mount list */ 133 struct vfsops *mnt_op; /* operations on fs */ 134 struct vfsconf *mnt_vfc; /* configuration info */ 135 struct vnode *mnt_vnodecovered; /* vnode we mounted on */ 136 struct vnodelst mnt_vnodelist; /* list of vnodes this mount */ 137 int mnt_flag; /* flags */ 138 int mnt_maxsymlinklen; /* max size of short symlink */ 139 struct statfs mnt_stat; /* cache of filesystem stats */ 140 qaddr_t mnt_data; /* private data */ 141/* struct vfsconf *mnt_vfc; */ /* configuration info */ 142 time_t mnt_time; /* last time written*/ 143}; 144 145/* 146 * Mount flags. 147 * 148 * Unmount uses MNT_FORCE flag. 149 */ 150#define MNT_RDONLY 0x00000001 /* read only filesystem */ 151#define MNT_SYNCHRONOUS 0x00000002 /* file system written synchronously */ 152#define MNT_NOEXEC 0x00000004 /* can't exec from filesystem */ 153#define MNT_NOSUID 0x00000008 /* don't honor setuid bits on fs */ 154#define MNT_NODEV 0x00000010 /* don't interpret special files */ 155#define MNT_UNION 0x00000020 /* union with underlying filesystem */ 156#define MNT_ASYNC 0x00000040 /* file system written asynchronously */ 157 158/* 159 * exported mount flags. 160 */ 161#define MNT_EXRDONLY 0x00000080 /* exported read only */ 162#define MNT_EXPORTED 0x00000100 /* file system is exported */ 163#define MNT_DEFEXPORTED 0x00000200 /* exported to the world */ 164#define MNT_EXPORTANON 0x00000400 /* use anon uid mapping for everyone */ 165#define MNT_EXKERB 0x00000800 /* exported with Kerberos uid mapping */ 166 167/* 168 * Flags set by internal operations. 169 */ 170#define MNT_LOCAL 0x00001000 /* filesystem is stored locally */ 171#define MNT_QUOTA 0x00002000 /* quotas are enabled on filesystem */ 172#define MNT_ROOTFS 0x00004000 /* identifies the root filesystem */ 173#define MNT_USER 0x00008000 /* mounted by a user */ 174 175/* 176 * Mask of flags that are visible to statfs() 177 */ 178#define MNT_VISFLAGMASK 0x0000ffff 179 180/* 181 * filesystem control flags. 182 * 183 * MNT_MLOCK lock the mount entry so that name lookup cannot proceed 184 * past the mount point. This keeps the subtree stable during mounts 185 * and unmounts. 186 */ 187#define MNT_UPDATE 0x00010000 /* not a real mount, just an update */ 188#define MNT_DELEXPORT 0x00020000 /* delete export host lists */ 189#define MNT_RELOAD 0x00040000 /* reload filesystem data */ 190#define MNT_FORCE 0x00080000 /* force unmount or readonly change */ 191#define MNT_MLOCK 0x00100000 /* lock so that subtree is stable */ 192#define MNT_MWAIT 0x00200000 /* someone is waiting for lock */ 193#define MNT_MPBUSY 0x00400000 /* scan of mount point in progress */ 194#define MNT_MPWANT 0x00800000 /* waiting for mount point */ 195#define MNT_UNMOUNT 0x01000000 /* unmount in progress */ 196#define MNT_WANTRDWR 0x02000000 /* want upgrade to read/write */ 197 198/* 199 * used to get configured filesystems information 200 */ 201#define VFS_MAXNAMELEN 32 202struct vfsconf { 203 void *vfc_vfsops; 204 char vfc_name[VFS_MAXNAMELEN]; 205 int vfc_index; 206 int vfc_refcount; 207 int vfc_flags; 208}; 209 210/* 211 * NB: these flags refer to IMPLEMENTATION properties, not properties of 212 * any actual mounts; i.e., it does not make sense to change the flags. 213 */ 214#define VFCF_STATIC 0x00000001 /* statically compiled into kernel */ 215#define VFCF_NETWORK 0x00000002 /* may get data over the network */ 216#define VFCF_READONLY 0x00000004 /* writes are not implemented */ 217#define VFCF_SYNTHETIC 0x00000008 /* data does not represent real files */ 218#define VFCF_LOOPBACK 0x00000010 /* aliases some other mounted FS */ 219#define VFCF_UNICODE 0x00000020 /* stores file names as Unicode*/ 220 221/* 222 * Operations supported on mounted file system. 223 */ 224#ifdef KERNEL 225 226extern int doforce; /* Flag to permit forcible unmounting. */ 227extern struct vfsconf void_vfsconf; 228extern struct vfsconf *vfsconf[]; 229 230#ifdef __STDC__ 231struct nameidata; 232struct mbuf; 233#endif 234 235struct vfsops { 236 int (*vfs_mount) __P((struct mount *mp, char *path, caddr_t data, 237 struct nameidata *ndp, struct proc *p)); 238 int (*vfs_start) __P((struct mount *mp, int flags, 239 struct proc *p)); 240 int (*vfs_unmount) __P((struct mount *mp, int mntflags, 241 struct proc *p)); 242 int (*vfs_root) __P((struct mount *mp, struct vnode **vpp)); 243 int (*vfs_quotactl) __P((struct mount *mp, int cmds, uid_t uid, 244 caddr_t arg, struct proc *p)); 245 int (*vfs_statfs) __P((struct mount *mp, struct statfs *sbp, 246 struct proc *p)); 247 int (*vfs_sync) __P((struct mount *mp, int waitfor, 248 struct ucred *cred, struct proc *p)); 249 int (*vfs_vget) __P((struct mount *mp, ino_t ino, 250 struct vnode **vpp)); 251 int (*vfs_fhtovp) __P((struct mount *mp, struct fid *fhp, 252 struct mbuf *nam, struct vnode **vpp, 253 int *exflagsp, struct ucred **credanonp)); 254 int (*vfs_vptofh) __P((struct vnode *vp, struct fid *fhp)); 255 int (*vfs_init) __P((void)); 256 int (*vfs_sysctl) __P((int *, u_int, void *, size_t *, void *, size_t, 257 struct proc *)); 258}; 259 260#define VFS_MOUNT(MP, PATH, DATA, NDP, P) \ 261 (*(MP)->mnt_op->vfs_mount)(MP, PATH, DATA, NDP, P) 262#define VFS_START(MP, FLAGS, P) (*(MP)->mnt_op->vfs_start)(MP, FLAGS, P) 263#define VFS_UNMOUNT(MP, FORCE, P) (*(MP)->mnt_op->vfs_unmount)(MP, FORCE, P) 264#define VFS_ROOT(MP, VPP) (*(MP)->mnt_op->vfs_root)(MP, VPP) 265#define VFS_QUOTACTL(MP,C,U,A,P) (*(MP)->mnt_op->vfs_quotactl)(MP, C, U, A, P) 266#define VFS_STATFS(MP, SBP, P) (*(MP)->mnt_op->vfs_statfs)(MP, SBP, P) 267#define VFS_SYNC(MP, WAIT, C, P) (*(MP)->mnt_op->vfs_sync)(MP, WAIT, C, P) 268#define VFS_VGET(MP, INO, VPP) (*(MP)->mnt_op->vfs_vget)(MP, INO, VPP) 269#define VFS_FHTOVP(MP, FIDP, NAM, VPP, EXFLG, CRED) \ 270 (*(MP)->mnt_op->vfs_fhtovp)(MP, FIDP, NAM, VPP, EXFLG, CRED) 271#define VFS_VPTOFH(VP, FIDP) (*(VP)->v_mount->mnt_op->vfs_vptofh)(VP, FIDP) 272 273#ifdef VFS_LKM 274#include <sys/conf.h> 275#include <sys/exec.h> 276#include <sys/sysent.h> 277#include <sys/lkm.h> 278 279#define VFS_SET(vfsops, fsname, index, flags) \ 280 static struct vfsconf _fs_vfsconf = { \ 281 &vfsops, \ 282 #fsname, \ 283 index, \ 284 0, \ 285 flags \ 286 }; \ 287 extern struct linker_set MODVNOPS; \ 288 MOD_VFS(#fsname,index,&MODVNOPS,&_fs_vfsconf); \ 289 int \ 290 fsname ## _mod(struct lkm_table *lkmtp, int cmd, int ver) { \ 291 DISPATCH(lkmtp, cmd, ver, nosys, nosys, nosys); } 292#else 293 294#define VFS_SET(vfsops, fsname, index, flags) \ 295 static struct vfsconf _fs_vfsconf = { \ 296 &vfsops, \ 297 #fsname, \ 298 index, \ 299 0, \ 300 flags | VFCF_STATIC \ 301 }; \ 302 DATA_SET(vfs_set,_fs_vfsconf) 303#endif /* VFS_LKM */ 304 305#endif /* KERNEL */ 306 307/* 308 * Flags for various system call interfaces. 309 * 310 * waitfor flags to vfs_sync() and getfsstat() 311 */ 312#define MNT_WAIT 1 313#define MNT_NOWAIT 2 314 315/* 316 * Generic file handle 317 */ 318struct fhandle { 319 fsid_t fh_fsid; /* File system id of mount point */ 320 struct fid fh_fid; /* File sys specific id */ 321}; 322typedef struct fhandle fhandle_t; 323 324#ifdef KERNEL 325#include <net/radix.h> 326#include <sys/socket.h> /* XXX for AF_MAX */ 327 328/* 329 * Network address lookup element 330 */ 331struct netcred { 332 struct radix_node netc_rnodes[2]; 333 int netc_exflags; 334 struct ucred netc_anon; 335}; 336 337/* 338 * Network export information 339 */ 340struct netexport { 341 struct netcred ne_defexported; /* Default export */ 342 struct radix_node_head *ne_rtable[AF_MAX+1]; /* Individual exports */ 343}; 344#endif /* KERNEL */ 345 346/* 347 * Export arguments for local filesystem mount calls. 348 */ 349struct export_args { 350 int ex_flags; /* export related flags */ 351 uid_t ex_root; /* mapping for root uid */ 352 struct ucred ex_anon; /* mapping for anonymous user */ 353 struct sockaddr *ex_addr; /* net address to which exported */ 354 int ex_addrlen; /* and the net address length */ 355 struct sockaddr *ex_mask; /* mask of valid bits in saddr */ 356 int ex_masklen; /* and the smask length */ 357}; 358 359/* 360 * Arguments to mount UFS-based filesystems 361 */ 362struct ufs_args { 363 char *fspec; /* block special device to mount */ 364 struct export_args export; /* network export information */ 365}; 366 367#ifdef MFS 368/* 369 * Arguments to mount MFS 370 */ 371struct mfs_args { 372 char *fspec; /* name to export for statfs */ 373 struct export_args export; /* if exported MFSes are supported */ 374 caddr_t base; /* base of file system in memory */ 375 u_long size; /* size of file system */ 376}; 377#endif /* MFS */ 378 379#ifdef MSDOSFS 380/* 381 * Arguments to mount MSDOS filesystems. 382 */ 383struct msdosfs_args { 384 char *fspec; /* blocks special holding the fs to mount */ 385 struct export_args export; /* network export information */ 386 uid_t uid; /* uid that owns msdosfs files */ 387 gid_t gid; /* gid that owns msdosfs files */ 388 mode_t mask; /* mask to be applied for msdosfs perms */ 389}; 390#endif 391 392#ifdef CD9660 393/* 394 * Arguments to mount ISO 9660 filesystems. 395 */ 396struct iso_args { 397 char *fspec; /* block special device to mount */ 398 struct export_args export; /* network export info */ 399 int flags; /* mounting flags, see below */ 400 401}; 402#define ISOFSMNT_NORRIP 0x00000001 /* disable Rock Ridge Ext.*/ 403#define ISOFSMNT_GENS 0x00000002 /* enable generation numbers */ 404#define ISOFSMNT_EXTATT 0x00000004 /* enable extended attributes */ 405#endif /* CD9660 */ 406 407#ifdef NFS 408/* 409 * Arguments to mount NFS 410 */ 411struct nfs_args { 412 struct sockaddr *addr; /* file server address */ 413 int addrlen; /* length of address */ 414 int sotype; /* Socket type */ 415 int proto; /* and Protocol */ 416 u_char *fh; /* File handle to be mounted */ 417 int fhsize; /* Size, in bytes, of fh */ 418 int flags; /* flags */ 419 int wsize; /* write size in bytes */ 420 int rsize; /* read size in bytes */ 421 int readdirsize; /* readdir size in bytes */ 422 int timeo; /* initial timeout in .1 secs */ 423 int retrans; /* times to retry send */ 424 int maxgrouplist; /* Max. size of group list */ 425 int readahead; /* # of blocks to readahead */ 426 int leaseterm; /* Term (sec) of lease */ 427 int deadthresh; /* Retrans threshold */ 428 char *hostname; /* server's name */ 429}; 430 431/* 432 * NFS mount option flags 433 */ 434#define NFSMNT_SOFT 0x00000001 /* soft mount (hard is default) */ 435#define NFSMNT_WSIZE 0x00000002 /* set write size */ 436#define NFSMNT_RSIZE 0x00000004 /* set read size */ 437#define NFSMNT_TIMEO 0x00000008 /* set initial timeout */ 438#define NFSMNT_RETRANS 0x00000010 /* set number of request retrys */ 439#define NFSMNT_MAXGRPS 0x00000020 /* set maximum grouplist size */ 440#define NFSMNT_INT 0x00000040 /* allow interrupts on hard mount */ 441#define NFSMNT_NOCONN 0x00000080 /* Don't Connect the socket */ 442#define NFSMNT_NQNFS 0x00000100 /* Use Nqnfs protocol */ 443#define NFSMNT_NFSV3 0x00000200 /* Use NFS Version 3 protocol */ 444#define NFSMNT_KERB 0x00000400 /* Use Kerberos authentication */ 445#define NFSMNT_DUMBTIMR 0x00000800 /* Don't estimate rtt dynamically */ 446#define NFSMNT_LEASETERM 0x00001000 /* set lease term (nqnfs) */ 447#define NFSMNT_READAHEAD 0x00002000 /* set read ahead */ 448#define NFSMNT_DEADTHRESH 0x00004000 /* set dead server retry thresh */ 449#define NFSMNT_RESVPORT 0x00008000 /* Allocate a reserved port */ 450#define NFSMNT_RDIRPLUS 0x00010000 /* Use Readdirplus for V3 */ 451#define NFSMNT_READDIRSIZE 0x00020000 /* Set readdir size */ 452#define NFSMNT_INTERNAL 0xfffc0000 /* Bits set internally */ 453#define NFSMNT_HASWRITEVERF 0x00040000 /* Has write verifier for V3 */ 454#define NFSMNT_GOTPATHCONF 0x00080000 /* Got the V3 pathconf info */ 455#define NFSMNT_GOTFSINFO 0x00100000 /* Got the V3 fsinfo */ 456#define NFSMNT_MNTD 0x00200000 /* Mnt server for mnt point */ 457#define NFSMNT_DISMINPROG 0x00400000 /* Dismount in progress */ 458#define NFSMNT_DISMNT 0x00800000 /* Dismounted */ 459#define NFSMNT_SNDLOCK 0x01000000 /* Send socket lock */ 460#define NFSMNT_WANTSND 0x02000000 /* Want above */ 461#define NFSMNT_RCVLOCK 0x04000000 /* Rcv socket lock */ 462#define NFSMNT_WANTRCV 0x08000000 /* Want above */ 463#define NFSMNT_WAITAUTH 0x10000000 /* Wait for authentication */ 464#define NFSMNT_HASAUTH 0x20000000 /* Has authenticator */ 465#define NFSMNT_WANTAUTH 0x40000000 /* Wants an authenticator */ 466#define NFSMNT_AUTHERR 0x80000000 /* Authentication error */ 467#endif /* NFS */ 468 469#ifdef KERNEL 470extern int (*mountroot) __P((caddr_t)); 471extern struct vfsops *mountrootvfsops; 472 473/* 474 * exported vnode operations 475 */ 476int dounmount __P((struct mount *, int, struct proc *)); 477struct mount *getvfs __P((fsid_t *)); /* return vfs given fsid */ 478void getnewfsid __P((struct mount *, int)); 479int vflush __P((struct mount *, struct vnode *, int)); 480int vfs_export /* process mount export info */ 481 __P((struct mount *, struct netexport *, struct export_args *)); 482struct netcred *vfs_export_lookup /* lookup host in fs export list */ 483 __P((struct mount *, struct netexport *, struct mbuf *)); 484int vfs_lock __P((struct mount *)); /* lock a vfs */ 485int vfs_mountedon __P((struct vnode *)); /* is a vfs mounted on vp */ 486int vfs_mountroot __P((caddr_t)); /* XXX goes away? */ 487void vfs_msync __P((struct mount *, int)); 488void vfs_unlock __P((struct mount *)); /* unlock a vfs */ 489void vfs_unmountall __P((void)); 490int vfs_busy __P((struct mount *)); /* mark a vfs busy */ 491void vfs_unbusy __P((struct mount *)); /* mark a vfs not busy */ 492extern CIRCLEQ_HEAD(mntlist, mount) mountlist; /* mounted filesystem list */ 493extern struct vfsops *vfssw[]; /* filesystem type table */ 494 495#else /* KERNEL */ 496 497#include <sys/cdefs.h> 498 499__BEGIN_DECLS 500int fstatfs __P((int, struct statfs *)); 501int getfh __P((const char *, fhandle_t *)); 502int getfsstat __P((struct statfs *, long, int)); 503int getmntinfo __P((struct statfs **, int)); 504int mount __P((int, const char *, int, void *)); 505int statfs __P((const char *, struct statfs *)); 506int unmount __P((const char *, int)); 507 508/* C library stuff */ 509struct vfsconf *getvfsbyname __P((const char *)); 510struct vfsconf *getvfsbytype __P((int)); 511struct vfsconf *getvfsent __P((void)); 512void setvfsent __P((int)); 513void endvfsent __P((void)); 514int vfsisloadable __P((const char *)); 515int vfsload __P((const char *)); 516__END_DECLS 517 518#endif /* KERNEL */ 519 520#endif /* !_SYS_MOUNT_H_ */ 521