NetBSD-5.0.2/sys/fs/efs/efs_dir.h
/* $NetBSD: efs_dir.h,v 1.1 2007/06/29 23:30:27 rumble 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_ */