| 1 | /* $NetBSD: efs.h,v 1.2 2007/06/30 15:56:16 rumble Exp $ */ |
| 2 | |
| 3 | /* |
| 4 | * Copyright (c) 2006 Stephen M. Rumble <rumble@ephemeral.org> |
| 5 | * |
| 6 | * Permission to use, copy, modify, and distribute this software for any |
| 7 | * purpose with or without fee is hereby granted, provided that the above |
| 8 | * copyright notice and this permission notice appear in all copies. |
| 9 | * |
| 10 | * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
| 11 | * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| 12 | * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR |
| 13 | * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| 14 | * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
| 15 | * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF |
| 16 | * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| 17 | */ |
| 18 | |
| 19 | /* |
| 20 | * See IRIX efs(4) |
| 21 | */ |
| 22 | |
| 23 | #ifndef _FS_EFS_EFS_H_ |
| 24 | #define _FS_EFS_EFS_H_ |
| 25 | |
| 26 | #define EFS_DEBUG |
| 27 | |
| 28 | /* |
| 29 | * SGI EFS - Extent File System |
| 30 | * |
| 31 | * The EFS filesystem is comprised of 512-byte sectors, or "basic blocks" (bb). |
| 32 | * These blocks are divided into cylinder groups (cg), from which extents are |
| 33 | * allocated. An extent is a contiguous region of blocks with minimal length |
| 34 | * of 1 and maximal length of 248. |
| 35 | * |
| 36 | * The filesystem is limited to 8GB by struct efs_extent's ex_bn field, which |
| 37 | * specifies an extent's offset in terms of basic blocks. Unfortunately, it was |
| 38 | * squished into a bitfield and given only 24bits so we are left with |
| 39 | * 2**24 * 512 bytes. Individual files are maximally 2GB, but not due to any |
| 40 | * limitation of on-disk structures. All sizes and offsets are stored as block, |
| 41 | * not byte values, with the exception of sb.sb_bmsize and efs_dinode.di_size. |
| 42 | * |
| 43 | * An EFS filesystem begins with the superblock (struct efs_sb) at bb offset 1 |
| 44 | * (offset 0 is reserved for bootblocks and other forms of contraband). The |
| 45 | * superblock contains various parameters including magic, checksum, filesystem |
| 46 | * size, number of cylinder groups, size of cylinder groups, and location of the |
| 47 | * first cylinder group. A bitmap may begin at offset bb 2. This is true of |
| 48 | * filesystems whose magic flag is EFS_MAGIC. However, the ability to grow an |
| 49 | * efs filesystem was added in IRIX 3.3 and a grown efs's bitmap is located |
| 50 | * toward the end of the disk, pointed to by sb.sb_bmblock. A grown filesystem |
| 51 | * is detected with the EFS_NEWMAGIC flag. See below for more details and |
| 52 | * differences. |
| 53 | * |
| 54 | * In order to promote inode and data locality, the disk is separated into |
| 55 | * sb.sb_ncg cylinder groups, which consist of sb.sb_cgfsize blocks each. |
| 56 | * The cylinder groups are laid out consecutively beginning from block offset |
| 57 | * sb.sb_firstcg. The beginning of each cylinder group is comprised of |
| 58 | * sb.sb_cgisize inodes (struct efs_dinode). The remaining space contains |
| 59 | * file extents, which are preferentially allocated to files whose inodes are |
| 60 | * within the same cylinder group. |
| 61 | * |
| 62 | * EFS increases I/O performance by storing files in contiguous chunks called |
| 63 | * 'extents' (struct efs_extent). Extents are variably sized from 1 to 248 |
| 64 | * blocks, but please don't ask me why 256 isn't the limit. |
| 65 | * |
| 66 | * Each inode (struct efs_dinode) contains space for twelve extent descriptors, |
| 67 | * allowing for up to 1,523,712 byte files (12 * 248 * 512) to be described |
| 68 | * without indirection. When indirection is employed, each of the twelve |
| 69 | * descriptors may reference extents that contain up to 248 more direct |
| 70 | * descriptors. Since each descriptor is 8 bytes we could theoretically have |
| 71 | * in total 15,872 * 12 direct descriptors, allowing for 15,872 * 12 * 248 * |
| 72 | * 512 = ~22GB files. However, since ei_numextents is a signed 16-bit quantity, |
| 73 | * we're limited to only 32767 indirect extents, which leaves us with a ~3.87GB |
| 74 | * maximum file size. (Of course, with a maximum filesystem size of 8GB, such a |
| 75 | * restriction isn't so bad.) Note that a single full indirect extent could |
| 76 | * reference approximately 1.877GB of data, but SGI strikes again! Earlier |
| 77 | * versions of IRIX (4.0.5H certainly, and perhaps prior) limit indirect |
| 78 | * extents to 32 basic blocks worth. This caps the number of extents at 12 * |
| 79 | * 32 * 64, permitting ~2.91GB files. SGI later raised this limit to 64 blocks |
| 80 | * worth, which exceeds the range of ei_numextents and gives a maximum |
| 81 | * theoretical file size of ~3.87GB. However, EFS purportedly only permits |
| 82 | * files up to 2GB in length. |
| 83 | * |
| 84 | * The bitmap referred to by sb_bmsize and (optionally) sb_bmblock contains |
| 85 | * data block allocation information. I haven't looked at this at all, nor |
| 86 | * am I aware of how inode allocation is performed. |
| 87 | * |
| 88 | * An EFS disk layout looks like the following: |
| 89 | * ____________________________________________________________________ |
| 90 | * | unused | superblock | bitmap | pad | cyl grp | ..cyl grps... | pad | |
| 91 | * -------------------------------------------------------------------- |
| 92 | * bb: 0 1 2 ^-sb.sb_firstcg sb.sb_size-^ |
| 93 | * |
| 94 | * A cylinder group looks like the following: |
| 95 | * ____________________________________________________________________ |
| 96 | * | inodes | ... extents and free space ... | |
| 97 | * -------------------------------------------------------------------- |
| 98 | * 0 ^-(sb.sb_cgisize * sb.sb_cgfsize-^ |
| 99 | * sizeof(struct efs_dinode)) |
| 100 | * |
| 101 | * So far as I am aware, EFS file systems have always been big endian, existing |
| 102 | * on mips (and perhaps earlier on m68k) machines only. While mips chips are |
| 103 | * bi-endian, I am unaware of any sgimips machine that was used in mipsel mode. |
| 104 | * |
| 105 | * See efs_sb.h, efs_dir.h, and efs_dinode.h for more information regarding |
| 106 | * directory layout and on-disk inodes, and the superblock accordingly. |
| 107 | */ |
| 108 | |
| 109 | /* |
| 110 | * Basic blocks are always 512 bytes. |
| 111 | */ |
| 112 | #define EFS_BB_SHFT 9 |
| 113 | #define EFS_BB_SIZE (1 << EFS_BB_SHFT) |
| 114 | |
| 115 | /* |
| 116 | * EFS basic block layout: |
| 117 | */ |
| 118 | #define EFS_BB_UNUSED 0 /* bb 0 is unused */ |
| 119 | #define EFS_BB_SB 1 /* bb 1 is superblock */ |
| 120 | #define EFS_BB_BITMAP 2 /* bb 2 is bitmap (unless moved by growfs) */ |
| 121 | /* bitmap continues, then padding up to first aligned cylinder group */ |
| 122 | |
| 123 | /* |
| 124 | * basic block <-> byte conversions |
| 125 | */ |
| 126 | #define EFS_BB2BY(_x) ((_x) << EFS_BB_SHFT) |
| 127 | #define EFS_BY2BB(_x) (((_x) + EFS_BB_SIZE - 1) >> EFS_BB_SHFT) |
| 128 | |
| 129 | /* |
| 130 | * Struct efs_extent limits us to 24 bit offsets, therefore the maximum |
| 131 | * efs.sb_size is 2**24 blocks (8GB). |
| 132 | * |
| 133 | * Trivia: IRIX's mkfs_efs(1M) has claimed the maximum to be 0xfffffe for years. |
| 134 | */ |
| 135 | #define EFS_SIZE_MAX 0x01000000 |
| 136 | |
| 137 | #ifdef _KERNEL |
| 138 | |
| 139 | #define VFSTOEFS(mp) ((struct efs_mount *)(mp)->mnt_data) |
| 140 | |
| 141 | /* debug goo */ |
| 142 | #ifdef DEBUG |
| 143 | #define EFS_DEBUG |
| 144 | #endif |
| 145 | #ifdef EFS_DEBUG |
| 146 | #define EFS_DPRINTF(_x) printf _x |
| 147 | #else |
| 148 | #define EFS_DPRINTF(_x) |
| 149 | #endif |
| 150 | |
| 151 | #endif |
| 152 | |
| 153 | #endif /* !_FS_EFS_EFS_H_ */ |