/* $NetBSD: efs_dir.h,v 1.2 2016/07/07 06:55:42 msaitoh Exp $ */ /* * Copyright (c) 2006 Stephen M. Rumble <rumble@ephemeral.org> * * Permission to use, copy, modify, and distribute this software for any * purpose with or without fee is hereby granted, provided that the above * copyright notice and this permission notice appear in all copies. * * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ /* * EFS directory block and directory entry formats. * * See IRIX dir(4) */ #ifndef _FS_EFS_EFS_DIR_H_ #define _FS_EFS_EFS_DIR_H_ /* * EFS directory block (512 bytes on disk) */ #define EFS_DIRBLK_MAGIC 0xbeef #define EFS_DIRBLK_SIZE EFS_BB_SIZE #define EFS_DIRBLK_HEADER_SIZE 4 #define EFS_DIRBLK_SPACE_SIZE (EFS_DIRBLK_SIZE - EFS_DIRBLK_HEADER_SIZE) struct efs_dirblk { uint16_t db_magic; /* must be EFS_DIRBLK_MAGIC */ uint8_t db_firstused; /* first dir entry offset (compacted) */ uint8_t db_slots; /* total number of entry offsets */ /* * The following db_space is used for three things: * 1) Array of entry offsets, one byte each, relative to the * efs_dirblk structure (not db_space!). These are stored right * shifted by one, thus providing 9 bits to address the entries. * 2) Array of even-sized directory entries, which exist at even * offsets, of course. * 3) Free space between the two arrays used for expanding either. * * The entry offsets exist in the lower offset range of de_space, * followed by efs_dirent structures higher up: * * db_space[sizeof(db_space)] _______________________ _ * | | | * | efs_dirent at z << 1 | | * |_______________________| | * | | | * | efs_dirent at x << 1 | |-- directory * | | | entries * |_______________________| | * | | | * | efs_dirent at y << 1 | | * db_space[db_firstused << 1] |_______________________| _| * | ... | * | free space | * | ... | * db_space[db_slots] |_______________________| _ * |___________z___________| | * |___________0___________| |-- directory * |___________y___________| | entry * db_space[0] |___________x___________| _| offsets * * In the above diagram, db_firstused would be equal to y. Note that * directory entry offsets need not occur in the same order as their * corresponding entries. The size of the offset array is indicated * by 'db_slots'. Unused slots in the middle of the array are zeroed. * * A range of free space between the end of the offset array and the * first directory entry is used for allocating new entry offsets and * directory entries. Its size is equal to ('db_firstused' << 1) - * 'db_slots'. * * When a directory entry is added, the directory offset array is * searched for a zeroed entry to use. If none is available and space * permits, it is allocated from the bottom of the free space region * and 'db_slots' is incremented. The space for the directory entry is * allocated from the top of free space, and the offset is stored. * * When a directory entry is removed, all directory entries below it * are moved up in order to expand the free space region. If the * corresponding entry offset borders the free space (it is last in the * array), it is coalesced into the free space region and 'db_slots' is * decremented. * * XXX when all entries removed, (how) do we free the dirblk? * * According to IRIX dir(4), the offset of a directory entry's offset * within the array of offsets does not change (say what?). That is, if * directory entry P's offset is contained in db_space[3], it will * remain in db_space[3] until it is removed. In other words, they do * not reshuffle the entry offsets in order to coalesce the unused * offset array entries into the free space region. Since we allocate * from zeroed ones before dipping into free space, this is typically * not a problem. However, it leaves open the case where many older * files are removed, thus leaving a valid array offset at the top, * which reduces free space and potentially keeps a large directory * entry from being added. Since there's no technical reason why moving * them around would violate the format, I'm guessing that IRIX does * some sort of caching of index offsets within the array. A few quick * tests seems to indicate that coalescing can be slightly more * performant. One could also sort array offsets by de_namelen and * binary search on lookup, but I am not sure how much performance could * be gained since there are only 72 entries at maximum, far less on * average, and many unix files have similar length. Quick tests show * no appreciable difference when using binary search, as one would * suspect. */ uint8_t db_space[EFS_DIRBLK_SPACE_SIZE]; } __packed; /* * 'db_slots' (directory entry offset array size) can be no larger * than (EFS_DIRBLK_SPACE_SIZE / 9), as each efs_dirent struct is * minimally 6 bytes and requires one 1-byte offset entry. */ #define EFS_DIRBLK_SLOTS_MAX (EFS_DIRBLK_SPACE_SIZE / 7) #define EFS_DIRBLK_SLOT_FREE (0) /* free, uncoalesced slots are zeroed */ /* * Directory entry structure, which resides in efs_dirblk->space. Minimally * 6 bytes on-disk, maximally 260 bytes. * * The allocation within efs_dirblk->space must always be even, so the * structure is always padded by one byte if the efs_dirent struct is odd. This * occurs when de_namelen is even. The macros below handle this irregularity. It * should be noted that despite this, de_namelen will always reflect the true * length of de_name, which is NOT nul-terminated. Therefore without a priori * knowledge of this scheme, one cannot accurately calculate the efs_dirent size * based on the de_namelen field alone, rather EFS_DIRENT_SIZE() must be used. */ struct efs_dirent { /* entry's inode number */ union { uint32_t l; uint16_t s[2]; } de_u; /* * de_name is of variable length (1 <= de_namelen <= 255). Note that * the string is NOT nul-terminated. */ uint8_t de_namelen; char de_name[1]; /* variably sized */ } __packed; #define de_inumber de_u.l #define EFS_DIRBLK_TO_DIRENT(_d, _o) (struct efs_dirent *)((char *)(_d) + _o) /* * Offsets are stored on-disk right shifted one to squeeze 512 even-byte * boundary offsets into a uint8_t. Before being compacted, the least * significant bits of an offset must, of course, be zero. */ #define EFS_DIRENT_OFF_SHFT 1 #define EFS_DIRENT_OFF_EXPND(_x) ((_x) << EFS_DIRENT_OFF_SHFT) #define EFS_DIRENT_OFF_COMPT(_x) ((_x) >> EFS_DIRENT_OFF_SHFT) #define EFS_DIRENT_OFF_VALID(_x) (((_x) & 0x1) == 0 && (_x) < \ EFS_DIRBLK_SPACE_SIZE) /*if expanded*/ #define EFS_DIRENT_NAMELEN_MAX 255 #define EFS_DIRENT_SIZE_MIN (sizeof(struct efs_dirent)) #define EFS_DIRENT_SIZE_MAX (EFS_DIRENT_SIZE_MIN+EFS_DIRENT_NAMELEN_MAX - 1) /* * Calculate the size of struct efs_dirent given the provided namelen. If our * namelen were even, then struct efs_dirent's size would be odd. In such a case * we must pad to ensure 16-bit alignment of the structure. */ #define EFS_DIRENT_SIZE(_x) (EFS_DIRENT_SIZE_MIN + (_x) - ((_x) & 0x1)) #endif /* !_FS_EFS_EFS_DIR_H_ */
