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NetBSD/sys/fs/efs/efs_extent.h

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Additional fixes/enhancements: 1) Comply with the way buffercache(9) is intended to be used. Now we read in single blocks of EFS_BB_SIZE, never taking in variable length extents with a single bread() call. 2) Handle symlinks with more than one extent. There's no reason for this to ever happen, but it's handled now. 3) Finally, add a hint to our iteration initialiser so we can start from the desired offset, rather than naively looping through from the beginning each time. Since we can binary search the correct location quickly, this improves large sequential reads by about 40% with 128MB files. Improvement should increase with file size.
2007-07-04 23:24:09 +04:00
/* $NetBSD: efs_extent.h,v 1.3 2007/07/04 19:24:09 rumble Exp $ */
Add read-only support for SGI's Extent File System. Reviewed by pooka@.
2007-06-30 03:30:16 +04:00
/*
* 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 extent descriptor format and sundry.
*
* See IRIX inode(4)
*/
#ifndef _FS_EFS_EFS_EXTENT_H_
#define _FS_EFS_EFS_EXTENT_H_
/*
* EFS on-disk extent descriptor (8 bytes)
*
* SGI smushed this structure's members into bit fields, but we have to
Additional documentation on extents and some artificial limitations SGI has introduced (and changed in backwards-incompatible ways) over the years.
2007-06-30 19:56:16 +04:00
* be a little more portable. Therefore we use the efs_extent (see below)
* type for in-core manipulation and convert immediately to and from disk.
Add read-only support for SGI's Extent File System. Reviewed by pooka@.
2007-06-30 03:30:16 +04:00
*/
struct efs_dextent {
union {
uint64_t ex_magic:8, /* magic number (always 0) */
ex_bn:24, /* bb number in filesystem */
ex_length:8, /* length of extent (in bb) */
ex_offset:24; /* logical file offset (in bb) */
uint8_t bytes[8];
uint32_t words[2];
} ex_muddle;
} __packed;
#define ex_bytes ex_muddle.bytes
#define ex_words ex_muddle.words
/*
* In-core, unsquished representation of an extent.
*/
struct efs_extent {
uint8_t ex_magic;
uint32_t ex_bn; /* NB: only 24 bits on disk */
uint8_t ex_length;
uint32_t ex_offset; /* NB: only 24 bits on disk */
};
#define EFS_EXTENT_MAGIC 0
#define EFS_EXTENT_BN_MASK 0x00ffffff
#define EFS_EXTENT_OFFSET_MASK 0x00ffffff
Additional fixes/enhancements: 1) Comply with the way buffercache(9) is intended to be used. Now we read in single blocks of EFS_BB_SIZE, never taking in variable length extents with a single bread() call. 2) Handle symlinks with more than one extent. There's no reason for this to ever happen, but it's handled now. 3) Finally, add a hint to our iteration initialiser so we can start from the desired offset, rather than naively looping through from the beginning each time. Since we can binary search the correct location quickly, this improves large sequential reads by about 40% with 128MB files. Improvement should increase with file size.
2007-07-04 23:24:09 +04:00
#define EFS_EXTENTS_PER_BB (EFS_BB_SIZE / sizeof(struct efs_dextent))
Add read-only support for SGI's Extent File System. Reviewed by pooka@.
2007-06-30 03:30:16 +04:00
#endif /* !_FS_EFS_EFS_EXTENT_H_ */