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diff --git a/share/man/man5/fs.5 b/share/man/man5/fs.5 new file mode 100644 index 0000000..ab8b96d --- /dev/null +++ b/share/man/man5/fs.5 @@ -0,0 +1,446 @@ +.\" Copyright (c) 1983, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)fs.5 8.2 (Berkeley) 4/19/94 +.\" $FreeBSD$ +.\" +.Dd October 31, 2006 +.Dt FS 5 +.Os +.Sh NAME +.Nm fs , +.Nm inode +.Nd format of file system volume +.Sh SYNOPSIS +.In sys/param.h +.In ufs/ffs/fs.h +.Pp +.In sys/types.h +.In sys/lock.h +.In sys/extattr.h +.In sys/acl.h +.In ufs/ufs/quota.h +.In ufs/ufs/dinode.h +.In ufs/ufs/extattr.h +.Sh DESCRIPTION +The files +.In fs.h +and +.In inode.h +declare several structures, defined variables and macros +which are used to create and manage the underlying format of +file system objects on random access devices (disks). +.Pp +The block size and number of blocks which +comprise a file system are parameters of the file system. +Sectors beginning at +.Dv BBLOCK +and continuing for +.Dv BBSIZE +are used +for a disklabel and for some hardware primary +and secondary bootstrapping programs. +.Pp +The actual file system begins at sector +.Dv SBLOCK +with the +.Em super-block +that is of size +.Dv SBLOCKSIZE . +The following structure describes the super-block and is +from the file +.In ufs/ffs/fs.h : +.Bd -literal +/* + * Super block for an FFS filesystem. + */ +struct fs { + int32_t fs_firstfield; /* historic filesystem linked list, */ + int32_t fs_unused_1; /* used for incore super blocks */ + int32_t fs_sblkno; /* offset of super-block in filesys */ + int32_t fs_cblkno; /* offset of cyl-block in filesys */ + int32_t fs_iblkno; /* offset of inode-blocks in filesys */ + int32_t fs_dblkno; /* offset of first data after cg */ + int32_t fs_old_cgoffset; /* cylinder group offset in cylinder */ + int32_t fs_old_cgmask; /* used to calc mod fs_ntrak */ + int32_t fs_old_time; /* last time written */ + int32_t fs_old_size; /* number of blocks in fs */ + int32_t fs_old_dsize; /* number of data blocks in fs */ + int32_t fs_ncg; /* number of cylinder groups */ + int32_t fs_bsize; /* size of basic blocks in fs */ + int32_t fs_fsize; /* size of frag blocks in fs */ + int32_t fs_frag; /* number of frags in a block in fs */ +/* these are configuration parameters */ + int32_t fs_minfree; /* minimum percentage of free blocks */ + int32_t fs_old_rotdelay; /* num of ms for optimal next block */ + int32_t fs_old_rps; /* disk revolutions per second */ +/* these fields can be computed from the others */ + int32_t fs_bmask; /* ``blkoff'' calc of blk offsets */ + int32_t fs_fmask; /* ``fragoff'' calc of frag offsets */ + int32_t fs_bshift; /* ``lblkno'' calc of logical blkno */ + int32_t fs_fshift; /* ``numfrags'' calc number of frags */ +/* these are configuration parameters */ + int32_t fs_maxcontig; /* max number of contiguous blks */ + int32_t fs_maxbpg; /* max number of blks per cyl group */ +/* these fields can be computed from the others */ + int32_t fs_fragshift; /* block to frag shift */ + int32_t fs_fsbtodb; /* fsbtodb and dbtofsb shift constant */ + int32_t fs_sbsize; /* actual size of super block */ + int32_t fs_spare1[2]; /* old fs_csmask */ + /* old fs_csshift */ + int32_t fs_nindir; /* value of NINDIR */ + int32_t fs_inopb; /* value of INOPB */ + int32_t fs_old_nspf; /* value of NSPF */ +/* yet another configuration parameter */ + int32_t fs_optim; /* optimization preference, see below */ + int32_t fs_old_npsect; /* # sectors/track including spares */ + int32_t fs_old_interleave; /* hardware sector interleave */ + int32_t fs_old_trackskew; /* sector 0 skew, per track */ + int32_t fs_id[2]; /* unique filesystem id */ +/* sizes determined by number of cylinder groups and their sizes */ + int32_t fs_old_csaddr; /* blk addr of cyl grp summary area */ + int32_t fs_cssize; /* size of cyl grp summary area */ + int32_t fs_cgsize; /* cylinder group size */ + int32_t fs_spare2; /* old fs_ntrak */ + int32_t fs_old_nsect; /* sectors per track */ + int32_t fs_old_spc; /* sectors per cylinder */ + int32_t fs_old_ncyl; /* cylinders in filesystem */ + int32_t fs_old_cpg; /* cylinders per group */ + int32_t fs_ipg; /* inodes per group */ + int32_t fs_fpg; /* blocks per group * fs_frag */ +/* this data must be re-computed after crashes */ + struct csum fs_old_cstotal; /* cylinder summary information */ +/* these fields are cleared at mount time */ + int8_t fs_fmod; /* super block modified flag */ + int8_t fs_clean; /* filesystem is clean flag */ + int8_t fs_ronly; /* mounted read-only flag */ + int8_t fs_old_flags; /* old FS_ flags */ + u_char fs_fsmnt[MAXMNTLEN]; /* name mounted on */ + u_char fs_volname[MAXVOLLEN]; /* volume name */ + uint64_t fs_swuid; /* system-wide uid */ + int32_t fs_pad; /* due to alignment of fs_swuid */ +/* these fields retain the current block allocation info */ + int32_t fs_cgrotor; /* last cg searched */ + void *fs_ocsp[NOCSPTRS]; /* padding; was list of fs_cs buffers */ + uint8_t *fs_contigdirs; /* # of contiguously allocated dirs */ + struct csum *fs_csp; /* cg summary info buffer for fs_cs */ + int32_t *fs_maxcluster; /* max cluster in each cyl group */ + u_int *fs_active; /* used by snapshots to track fs */ + int32_t fs_old_cpc; /* cyl per cycle in postbl */ + int32_t fs_maxbsize; /* maximum blocking factor permitted */ + int64_t fs_unrefs; /* number of unreferenced inodes */ + int64_t fs_sparecon64[16]; /* old rotation block list head */ + int64_t fs_sblockloc; /* byte offset of standard superblock */ + struct csum_total fs_cstotal; /* cylinder summary information */ + ufs_time_t fs_time; /* last time written */ + int64_t fs_size; /* number of blocks in fs */ + int64_t fs_dsize; /* number of data blocks in fs */ + ufs2_daddr_t fs_csaddr; /* blk addr of cyl grp summary area */ + int64_t fs_pendingblocks; /* blocks in process of being freed */ + int32_t fs_pendinginodes; /* inodes in process of being freed */ + int32_t fs_snapinum[FSMAXSNAP]; /* list of snapshot inode numbers */ + int32_t fs_avgfilesize; /* expected average file size */ + int32_t fs_avgfpdir; /* expected # of files per directory */ + int32_t fs_save_cgsize; /* save real cg size to use fs_bsize */ + int32_t fs_sparecon32[26]; /* reserved for future constants */ + int32_t fs_flags; /* see FS_ flags below */ + int32_t fs_contigsumsize; /* size of cluster summary array */ + int32_t fs_maxsymlinklen; /* max length of an internal symlink */ + int32_t fs_old_inodefmt; /* format of on-disk inodes */ + uint64_t fs_maxfilesize; /* maximum representable file size */ + int64_t fs_qbmask; /* ~fs_bmask for use with 64-bit size */ + int64_t fs_qfmask; /* ~fs_fmask for use with 64-bit size */ + int32_t fs_state; /* validate fs_clean field */ + int32_t fs_old_postblformat; /* format of positional layout tables */ + int32_t fs_old_nrpos; /* number of rotational positions */ + int32_t fs_spare5[2]; /* old fs_postbloff */ + /* old fs_rotbloff */ + int32_t fs_magic; /* magic number */ +}; + +/* + * Filesystem identification + */ +#define FS_UFS1_MAGIC 0x011954 /* UFS1 fast filesystem magic number */ +#define FS_UFS2_MAGIC 0x19540119 /* UFS2 fast filesystem magic number */ +#define FS_OKAY 0x7c269d38 /* superblock checksum */ +#define FS_42INODEFMT -1 /* 4.2BSD inode format */ +#define FS_44INODEFMT 2 /* 4.4BSD inode format */ + +/* + * Preference for optimization. + */ +#define FS_OPTTIME 0 /* minimize allocation time */ +#define FS_OPTSPACE 1 /* minimize disk fragmentation */ +.Ed +.Pp +Each disk drive contains some number of file systems. +A file system consists of a number of cylinder groups. +Each cylinder group has inodes and data. +.Pp +A file system is described by its super-block, which in turn +describes the cylinder groups. +The super-block is critical +data and is replicated in each cylinder group to protect against +catastrophic loss. +This is done at file system creation +time and the critical +super-block data does not change, so the copies need not be +referenced further unless disaster strikes. +.Pp +Addresses stored in inodes are capable of addressing fragments +of `blocks'. +File system blocks of at most size +.Dv MAXBSIZE +can +be optionally broken into 2, 4, or 8 pieces, each of which is +addressable; these pieces may be +.Dv DEV_BSIZE , +or some multiple of +a +.Dv DEV_BSIZE +unit. +.Pp +Large files consist of exclusively large data blocks. +To avoid +undue wasted disk space, the last data block of a small file is +allocated as only as many fragments of a large block as are +necessary. +The file system format retains only a single pointer +to such a fragment, which is a piece of a single large block that +has been divided. +The size of such a fragment is determinable from +information in the inode, using the +.Fn blksize fs ip lbn +macro. +.Pp +The file system records space availability at the fragment level; +to determine block availability, aligned fragments are examined. +.Pp +The root inode is the root of the file system. +Inode 0 cannot be used for normal purposes and +historically bad blocks were linked to inode 1, +thus the root inode is 2 (inode 1 is no longer used for +this purpose, however numerous dump tapes make this +assumption, so we are stuck with it). +.Pp +The +.Fa fs_minfree +element gives the minimum acceptable percentage of file system +blocks that may be free. +If the freelist drops below this level +only the super-user may continue to allocate blocks. +The +.Fa fs_minfree +element +may be set to 0 if no reserve of free blocks is deemed necessary, +however severe performance degradations will be observed if the +file system is run at greater than 90% full; thus the default +value of +.Fa fs_minfree +is 10%. +.Pp +Empirically the best trade-off between block fragmentation and +overall disk utilization at a loading of 90% comes with a +fragmentation of 8, thus the default fragment size is an eighth +of the block size. +.Pp +The element +.Fa fs_optim +specifies whether the file system should try to minimize the time spent +allocating blocks, or if it should attempt to minimize the space +fragmentation on the disk. +If the value of fs_minfree (see above) is less than 10%, +then the file system defaults to optimizing for space to avoid +running out of full sized blocks. +If the value of minfree is greater than or equal to 10%, +fragmentation is unlikely to be problematical, and +the file system defaults to optimizing for time. +.Pp +.Em Cylinder group related limits : +Each cylinder keeps track of the availability of blocks at different +rotational positions, so that sequential blocks can be laid out +with minimum rotational latency. +With the default of 8 distinguished +rotational positions, the resolution of the +summary information is 2ms for a typical 3600 rpm drive. +.Pp +The element +.Fa fs_old_rotdelay +gives the minimum number of milliseconds to initiate +another disk transfer on the same cylinder. +It is used in determining the rotationally optimal +layout for disk blocks within a file; +the default value for +.Fa fs_old_rotdelay +is 2ms. +.Pp +Each file system has a statically allocated number of inodes. +An inode is allocated for each +.Dv NBPI +bytes of disk space. +The inode allocation strategy is extremely conservative. +.Pp +.Dv MINBSIZE +is the smallest allowable block size. +With a +.Dv MINBSIZE +of 4096 +it is possible to create files of size +2^32 with only two levels of indirection. +.Dv MINBSIZE +must be big enough to hold a cylinder group block, +thus changes to +.Pq Fa struct cg +must keep its size within +.Dv MINBSIZE . +Note that super-blocks are never more than size +.Dv SBLOCKSIZE . +.Pp +The path name on which the file system is mounted is maintained in +.Fa fs_fsmnt . +.Dv MAXMNTLEN +defines the amount of space allocated in +the super-block for this name. +The limit on the amount of summary information per file system +is defined by +.Dv MAXCSBUFS . +For a 4096 byte block size, it is currently parameterized for a +maximum of two million cylinders. +.Pp +Per cylinder group information is summarized in blocks allocated +from the first cylinder group's data blocks. +These blocks are read in from +.Fa fs_csaddr +(size +.Fa fs_cssize ) +in addition to the super-block. +.Pp +.Sy N.B. : +.Fn sizeof "struct csum" +must be a power of two in order for +the +.Fn fs_cs +macro to work. +.Pp +The +.Em "Super-block for a file system" : +The size of the rotational layout tables +is limited by the fact that the super-block is of size +.Dv SBLOCKSIZE . +The size of these tables is +.Em inversely +proportional to the block +size of the file system. +The size of the tables is +increased when sector sizes are not powers of two, +as this increases the number of cylinders +included before the rotational pattern repeats +.Pq Fa fs_cpc . +The size of the rotational layout +tables is derived from the number of bytes remaining in +.Pq Fa struct fs . +.Pp +The number of blocks of data per cylinder group +is limited because cylinder groups are at most one block. +The inode and free block tables +must fit into a single block after deducting space for +the cylinder group structure +.Pq Fa struct cg . +.Pp +The +.Em Inode : +The inode is the focus of all file activity in the +.Ux +file system. +There is a unique inode allocated +for each active file, +each current directory, each mounted-on file, +text file, and the root. +An inode is `named' by its device/i-number pair. +For further information, see the include file +.In ufs/ufs/inode.h . +.Pp +The format of an external attribute is defined by the extattr structure: +.Bd -literal +struct extattr { + int32_t ea_length; /* length of this attribute */ + int8_t ea_namespace; /* name space of this attribute */ + int8_t ea_contentpadlen; /* padding at end of attribute */ + int8_t ea_namelength; /* length of attribute name */ + char ea_name[1]; /* null-terminated attribute name */ + /* extended attribute content follows */ +}; +.Ed +.Pp +Several macros are defined to manipulate these structures. +Each macro takes a pointer to an extattr structure. +.Bl -tag -width ".Dv EXTATTR_SET_LENGTHS(eap, size)" +.It Dv EXTATTR_NEXT(eap) +Returns a pointer to the next extended attribute following +.Fa eap . +.It Dv EXTATTR_CONTENT(eap) +Returns a pointer to the extended attribute content referenced by +.Fa eap . +.It Dv EXTATTR_CONTENT_SIZE(eap) +Returns the size of the extended attribute content referenced by +.Fa eap . +.It Dv EXTATTR_SET_LENGTHS(eap, size) +Called with the size of the attribute content after initializing +the attribute name to calculate and set the +.Fa ea_length , +.Fa ea_namelength , +and +.Fa ea_contentpadlen +fields of the extended attribute structure. +.El +.Pp +The following code identifies an ACL: +.Bd -literal + if (eap->ea_namespace == EXTATTR_NAMESPACE_SYSTEM && + !strcmp(eap->ea_name, POSIX1E_ACL_ACCESS_EXTATTR_NAME) { + aclp = EXTATTR_CONTENT(eap); + acllen = EXTATTR_CONTENT_SIZE(eap); + ... + } +.Ed +.Pp +The following code creates an extended attribute +containing a copy of a structure +.Fa mygif : +.Bd -literal + eap->ea_namespace = EXTATTR_NAMESPACE_USER; + strcpy(eap->ea_name, "filepic.gif"); + EXTATTR_SET_LENGTHS(eap, sizeof(struct mygif)); + memcpy(EXTATTR_CONTENT(eap), &mygif, sizeof(struct mygif)); +.Ed +.Sh HISTORY +A super-block structure named filsys appeared in +.At v6 . +The file system described in this manual appeared +in +.Bx 4.2 . |
