1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)fs.5 8.2 (Berkeley) 4/19/94 29.\" 30.Dd January 16, 2017 31.Dt FS 5 32.Os 33.Sh NAME 34.Nm fs , 35.Nm inode 36.Nd format of file system volume 37.Sh SYNOPSIS 38.In sys/param.h 39.In ufs/ffs/fs.h 40.Pp 41.In sys/types.h 42.In sys/lock.h 43.In sys/extattr.h 44.In sys/acl.h 45.In ufs/ufs/quota.h 46.In ufs/ufs/dinode.h 47.In ufs/ufs/extattr.h 48.Sh DESCRIPTION 49The files 50.In fs.h 51and 52.In inode.h 53declare several structures, defined variables and macros 54which are used to create and manage the underlying format of 55file system objects on random access devices (disks). 56.Pp 57The block size and number of blocks which 58comprise a file system are parameters of the file system. 59Sectors beginning at 60.Dv BBLOCK 61and continuing for 62.Dv BBSIZE 63are used 64for a disklabel and for some hardware primary 65and secondary bootstrapping programs. 66.Pp 67The actual file system begins at sector 68.Dv SBLOCK 69with the 70.Em super-block 71that is of size 72.Dv SBLOCKSIZE . 73The following structure describes the super-block and is 74from the file 75.In ufs/ffs/fs.h : 76.Bd -literal 77/* 78 * Super block for an FFS filesystem. 79 */ 80struct fs { 81 int32_t fs_firstfield; /* historic filesystem linked list, */ 82 int32_t fs_unused_1; /* used for incore super blocks */ 83 int32_t fs_sblkno; /* offset of super-block in filesys */ 84 int32_t fs_cblkno; /* offset of cyl-block in filesys */ 85 int32_t fs_iblkno; /* offset of inode-blocks in filesys */ 86 int32_t fs_dblkno; /* offset of first data after cg */ 87 int32_t fs_old_cgoffset; /* cylinder group offset in cylinder */ 88 int32_t fs_old_cgmask; /* used to calc mod fs_ntrak */ 89 int32_t fs_old_time; /* last time written */ 90 int32_t fs_old_size; /* number of blocks in fs */ 91 int32_t fs_old_dsize; /* number of data blocks in fs */ 92 int32_t fs_ncg; /* number of cylinder groups */ 93 int32_t fs_bsize; /* size of basic blocks in fs */ 94 int32_t fs_fsize; /* size of frag blocks in fs */ 95 int32_t fs_frag; /* number of frags in a block in fs */ 96/* these are configuration parameters */ 97 int32_t fs_minfree; /* minimum percentage of free blocks */ 98 int32_t fs_old_rotdelay; /* num of ms for optimal next block */ 99 int32_t fs_old_rps; /* disk revolutions per second */ 100/* these fields can be computed from the others */ 101 int32_t fs_bmask; /* ``blkoff'' calc of blk offsets */ 102 int32_t fs_fmask; /* ``fragoff'' calc of frag offsets */ 103 int32_t fs_bshift; /* ``lblkno'' calc of logical blkno */ 104 int32_t fs_fshift; /* ``numfrags'' calc number of frags */ 105/* these are configuration parameters */ 106 int32_t fs_maxcontig; /* max number of contiguous blks */ 107 int32_t fs_maxbpg; /* max number of blks per cyl group */ 108/* these fields can be computed from the others */ 109 int32_t fs_fragshift; /* block to frag shift */ 110 int32_t fs_fsbtodb; /* fsbtodb and dbtofsb shift constant */ 111 int32_t fs_sbsize; /* actual size of super block */ 112 int32_t fs_spare1[2]; /* old fs_csmask */ 113 /* old fs_csshift */ 114 int32_t fs_nindir; /* value of NINDIR */ 115 int32_t fs_inopb; /* value of INOPB */ 116 int32_t fs_old_nspf; /* value of NSPF */ 117/* yet another configuration parameter */ 118 int32_t fs_optim; /* optimization preference, see below */ 119 int32_t fs_old_npsect; /* # sectors/track including spares */ 120 int32_t fs_old_interleave; /* hardware sector interleave */ 121 int32_t fs_old_trackskew; /* sector 0 skew, per track */ 122 int32_t fs_id[2]; /* unique filesystem id */ 123/* sizes determined by number of cylinder groups and their sizes */ 124 int32_t fs_old_csaddr; /* blk addr of cyl grp summary area */ 125 int32_t fs_cssize; /* size of cyl grp summary area */ 126 int32_t fs_cgsize; /* cylinder group size */ 127 int32_t fs_spare2; /* old fs_ntrak */ 128 int32_t fs_old_nsect; /* sectors per track */ 129 int32_t fs_old_spc; /* sectors per cylinder */ 130 int32_t fs_old_ncyl; /* cylinders in filesystem */ 131 int32_t fs_old_cpg; /* cylinders per group */ 132 int32_t fs_ipg; /* inodes per group */ 133 int32_t fs_fpg; /* blocks per group * fs_frag */ 134/* this data must be re-computed after crashes */ 135 struct csum fs_old_cstotal; /* cylinder summary information */ 136/* these fields are cleared at mount time */ 137 int8_t fs_fmod; /* super block modified flag */ 138 int8_t fs_clean; /* filesystem is clean flag */ 139 int8_t fs_ronly; /* mounted read-only flag */ 140 int8_t fs_old_flags; /* old FS_ flags */ 141 u_char fs_fsmnt[MAXMNTLEN]; /* name mounted on */ 142 u_char fs_volname[MAXVOLLEN]; /* volume name */ 143 uint64_t fs_swuid; /* system-wide uid */ 144 int32_t fs_pad; /* due to alignment of fs_swuid */ 145/* these fields retain the current block allocation info */ 146 int32_t fs_cgrotor; /* last cg searched */ 147 void *fs_ocsp[NOCSPTRS]; /* padding; was list of fs_cs buffers */ 148 uint8_t *fs_contigdirs; /* # of contiguously allocated dirs */ 149 struct csum *fs_csp; /* cg summary info buffer for fs_cs */ 150 int32_t *fs_maxcluster; /* max cluster in each cyl group */ 151 u_int *fs_active; /* used by snapshots to track fs */ 152 int32_t fs_old_cpc; /* cyl per cycle in postbl */ 153 int32_t fs_maxbsize; /* maximum blocking factor permitted */ 154 int64_t fs_unrefs; /* number of unreferenced inodes */ 155 int64_t fs_sparecon64[16]; /* old rotation block list head */ 156 int64_t fs_sblockloc; /* byte offset of standard superblock */ 157 struct csum_total fs_cstotal; /* cylinder summary information */ 158 ufs_time_t fs_time; /* last time written */ 159 int64_t fs_size; /* number of blocks in fs */ 160 int64_t fs_dsize; /* number of data blocks in fs */ 161 ufs2_daddr_t fs_csaddr; /* blk addr of cyl grp summary area */ 162 int64_t fs_pendingblocks; /* blocks in process of being freed */ 163 int32_t fs_pendinginodes; /* inodes in process of being freed */ 164 int32_t fs_snapinum[FSMAXSNAP]; /* list of snapshot inode numbers */ 165 int32_t fs_avgfilesize; /* expected average file size */ 166 int32_t fs_avgfpdir; /* expected # of files per directory */ 167 int32_t fs_save_cgsize; /* save real cg size to use fs_bsize */ 168 int32_t fs_sparecon32[26]; /* reserved for future constants */ 169 int32_t fs_flags; /* see FS_ flags below */ 170 int32_t fs_contigsumsize; /* size of cluster summary array */ 171 int32_t fs_maxsymlinklen; /* max length of an internal symlink */ 172 int32_t fs_old_inodefmt; /* format of on-disk inodes */ 173 uint64_t fs_maxfilesize; /* maximum representable file size */ 174 int64_t fs_qbmask; /* ~fs_bmask for use with 64-bit size */ 175 int64_t fs_qfmask; /* ~fs_fmask for use with 64-bit size */ 176 int32_t fs_state; /* validate fs_clean field */ 177 int32_t fs_old_postblformat; /* format of positional layout tables */ 178 int32_t fs_old_nrpos; /* number of rotational positions */ 179 int32_t fs_spare5[2]; /* old fs_postbloff */ 180 /* old fs_rotbloff */ 181 int32_t fs_magic; /* magic number */ 182}; 183 184/* 185 * Filesystem identification 186 */ 187#define FS_UFS1_MAGIC 0x011954 /* UFS1 fast filesystem magic number */ 188#define FS_UFS2_MAGIC 0x19540119 /* UFS2 fast filesystem magic number */ 189#define FS_OKAY 0x7c269d38 /* superblock checksum */ 190#define FS_42INODEFMT -1 /* 4.2BSD inode format */ 191#define FS_44INODEFMT 2 /* 4.4BSD inode format */ 192 193/* 194 * Preference for optimization. 195 */ 196#define FS_OPTTIME 0 /* minimize allocation time */ 197#define FS_OPTSPACE 1 /* minimize disk fragmentation */ 198.Ed 199.Pp 200Each disk drive contains some number of file systems. 201A file system consists of a number of cylinder groups. 202Each cylinder group has inodes and data. 203.Pp 204A file system is described by its super-block, which in turn 205describes the cylinder groups. 206The super-block is critical 207data and is replicated in each cylinder group to protect against 208catastrophic loss. 209This is done at file system creation 210time and the critical 211super-block data does not change, so the copies need not be 212referenced further unless disaster strikes. 213.Pp 214Addresses stored in inodes are capable of addressing fragments 215of `blocks'. 216File system blocks of at most size 217.Dv MAXBSIZE 218can 219be optionally broken into 2, 4, or 8 pieces, each of which is 220addressable; these pieces may be 221.Dv DEV_BSIZE , 222or some multiple of 223a 224.Dv DEV_BSIZE 225unit. 226.Pp 227Large files consist of exclusively large data blocks. 228To avoid 229undue wasted disk space, the last data block of a small file is 230allocated as only as many fragments of a large block as are 231necessary. 232The file system format retains only a single pointer 233to such a fragment, which is a piece of a single large block that 234has been divided. 235The size of such a fragment is determinable from 236information in the inode, using the 237.Fn blksize fs ip lbn 238macro. 239.Pp 240The file system records space availability at the fragment level; 241to determine block availability, aligned fragments are examined. 242.Pp 243The root inode is the root of the file system. 244Inode 0 cannot be used for normal purposes and 245historically bad blocks were linked to inode 1, 246thus the root inode is 2 (inode 1 is no longer used for 247this purpose, however numerous dump tapes make this 248assumption, so we are stuck with it). 249.Pp 250The 251.Fa fs_minfree 252element gives the minimum acceptable percentage of file system 253blocks that may be free. 254If the freelist drops below this level 255only the super-user may continue to allocate blocks. 256The 257.Fa fs_minfree 258element 259may be set to 0 if no reserve of free blocks is deemed necessary, 260however severe performance degradations will be observed if the 261file system is run at greater than 90% full; thus the default 262value of 263.Fa fs_minfree 264is 8%. 265.Pp 266Empirically the best trade-off between block fragmentation and 267overall disk utilization at a loading of 90% comes with a 268fragmentation of 8, thus the default fragment size is an eighth 269of the block size. 270.Pp 271The element 272.Fa fs_optim 273specifies whether the file system should try to minimize the time spent 274allocating blocks, or if it should attempt to minimize the space 275fragmentation on the disk. 276If the value of fs_minfree (see above) is less than 8%, 277then the file system defaults to optimizing for space to avoid 278running out of full sized blocks. 279If the value of minfree is greater than or equal to 8%, 280fragmentation is unlikely to be problematical, and 281the file system defaults to optimizing for time. 282.Pp 283.Em Cylinder group related limits : 284Each cylinder keeps track of the availability of blocks at different 285rotational positions, so that sequential blocks can be laid out 286with minimum rotational latency. 287With the default of 8 distinguished 288rotational positions, the resolution of the 289summary information is 2ms for a typical 3600 rpm drive. 290.Pp 291The element 292.Fa fs_old_rotdelay 293gives the minimum number of milliseconds to initiate 294another disk transfer on the same cylinder. 295It is used in determining the rotationally optimal 296layout for disk blocks within a file; 297the default value for 298.Fa fs_old_rotdelay 299is 2ms. 300.Pp 301Each file system has a statically allocated number of inodes. 302An inode is allocated for each 303.Dv NBPI 304bytes of disk space. 305The inode allocation strategy is extremely conservative. 306.Pp 307.Dv MINBSIZE 308is the smallest allowable block size. 309With a 310.Dv MINBSIZE 311of 4096 312it is possible to create files of size 3132^32 with only two levels of indirection. 314.Dv MINBSIZE 315must be big enough to hold a cylinder group block, 316thus changes to 317.Pq Fa struct cg 318must keep its size within 319.Dv MINBSIZE . 320Note that super-blocks are never more than size 321.Dv SBLOCKSIZE . 322.Pp 323The path name on which the file system is mounted is maintained in 324.Fa fs_fsmnt . 325.Dv MAXMNTLEN 326defines the amount of space allocated in 327the super-block for this name. 328The limit on the amount of summary information per file system 329is defined by 330.Dv MAXCSBUFS . 331For a 4096 byte block size, it is currently parameterized for a 332maximum of two million cylinders. 333.Pp 334Per cylinder group information is summarized in blocks allocated 335from the first cylinder group's data blocks. 336These blocks are read in from 337.Fa fs_csaddr 338(size 339.Fa fs_cssize ) 340in addition to the super-block. 341.Pp 342.Sy N.B. : 343.Fn sizeof "struct csum" 344must be a power of two in order for 345the 346.Fn fs_cs 347macro to work. 348.Pp 349The 350.Em "Super-block for a file system" : 351The size of the rotational layout tables 352is limited by the fact that the super-block is of size 353.Dv SBLOCKSIZE . 354The size of these tables is 355.Em inversely 356proportional to the block 357size of the file system. 358The size of the tables is 359increased when sector sizes are not powers of two, 360as this increases the number of cylinders 361included before the rotational pattern repeats 362.Pq Fa fs_cpc . 363The size of the rotational layout 364tables is derived from the number of bytes remaining in 365.Pq Fa struct fs . 366.Pp 367The number of blocks of data per cylinder group 368is limited because cylinder groups are at most one block. 369The inode and free block tables 370must fit into a single block after deducting space for 371the cylinder group structure 372.Pq Fa struct cg . 373.Pp 374The 375.Em Inode : 376The inode is the focus of all file activity in the 377.Ux 378file system. 379There is a unique inode allocated 380for each active file, 381each current directory, each mounted-on file, 382text file, and the root. 383An inode is `named' by its device/i-number pair. 384For further information, see the include file 385.In ufs/ufs/inode.h . 386.Pp 387The format of an external attribute is defined by the extattr structure: 388.Bd -literal 389struct extattr { 390 uint32_t ea_length; /* length of this attribute */ 391 uint8_t ea_namespace; /* name space of this attribute */ 392 uint8_t ea_contentpadlen; /* bytes of padding at end of attribute */ 393 uint8_t ea_namelength; /* length of attribute name */ 394 char ea_name[1]; /* attribute name (NOT nul-terminated) */ 395 /* padding, if any, to align attribute content to 8 byte boundary */ 396 /* extended attribute content follows */ 397}; 398.Ed 399.Pp 400Several macros are defined to manipulate these structures. 401Each macro takes a pointer to an extattr structure. 402.Bl -tag -width ".Dv EXTATTR_CONTENT_SIZE(eap)" 403.It Dv EXTATTR_NEXT(eap) 404Returns a pointer to the next extended attribute following 405.Fa eap . 406.It Dv EXTATTR_CONTENT(eap) 407Returns a pointer to the extended attribute content referenced by 408.Fa eap . 409.It Dv EXTATTR_CONTENT_SIZE(eap) 410Returns the size of the extended attribute content referenced by 411.Fa eap . 412.El 413.Pp 414The following code identifies an ACL: 415.Bd -literal 416 if (eap->ea_namespace == EXTATTR_NAMESPACE_SYSTEM && 417 eap->ea_namelength == sizeof(POSIX1E_ACL_ACCESS_EXTATTR_NAME) - 1 && 418 strncmp(eap->ea_name, POSIX1E_ACL_ACCESS_EXTATTR_NAME, 419 sizeof(POSIX1E_ACL_ACCESS_EXTATTR_NAME) - 1) == 0) { 420 aclp = EXTATTR_CONTENT(eap); 421 acllen = EXTATTR_CONTENT_SIZE(eap); 422 ... 423 } 424.Ed 425.Sh HISTORY 426A super-block structure named filsys appeared in 427.At v6 . 428The file system described in this manual appeared 429in 430.Bx 4.2 . 431