Initial commit: Schunix as it stands before the SchOS rename
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
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Nexoniarz
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203
include/fs.h
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203
include/fs.h
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// SCHFS - On-disk file system format.
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// Both the kernel and user programs use this header file.
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//
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// Changes from original:
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// - struct dinode gains atime, mtime, ctime (timestamps) and checksum
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// (CRC32c). Padding reduced from 44 to 28 bytes; struct stays 128 bytes.
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// - struct superblock gains checksum field.
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// - struct fsv1_extent added for T_EXTENT inode block mapping.
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// - OVERFLOW_DIR_START / OVERFLOW_DIR_END replace the bare "113 * BSIZE"
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// magic numbers used in fs.c and mkfs.c.
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#ifndef FS_H
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#define FS_H
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#define ROOTINO 1 // root i-number
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#define BSIZE 1024 // block size
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// Permission mode bits (rwmode field)
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#define RW 3 // 11 read+write
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#define W_ 1 // 01 write-only
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#define R_ 2 // 10 read-only
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#define NONE 0 // 00 no access
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// ---------------------------------------------------------------------------
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// Superblock
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// ---------------------------------------------------------------------------
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// Disk layout:
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// [ boot | super | log | inode-bitmap | inode-blocks | block-bitmap | data ]
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struct superblock {
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uint magic; // Must be FSMAGIC
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uint size; // Size of file system image (blocks)
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uint nblocks; // Number of data blocks
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uint ninodes; // Number of inodes
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uint nlog; // Number of log blocks
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uint logstart; // Block number of first log block
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uint inodestart; // Block number of first inode block
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uint bmapstart; // Block number of first free-block bitmap block
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uint ibmapstart; // Block number of first inode-bitmap block
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uint freeinodes; // Count of free inodes
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uint freeblocks; // Count of free blocks
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uint checksum; // CRC32c of this struct (field zeroed during computation)
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};
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extern struct superblock sb;
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#define FSMAGIC 0x10203040
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// ---------------------------------------------------------------------------
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// Block / inode geometry
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// ---------------------------------------------------------------------------
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#define NDIRECT 12
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#define NINDIRECT (BSIZE / sizeof(uint))
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// Maximum file size in blocks: direct + 1x + 2x + 3x indirect
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#define MAXFILE (NDIRECT \
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+ NINDIRECT \
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+ (NINDIRECT * NINDIRECT) \
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+ (NINDIRECT * NINDIRECT * NINDIRECT))
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// ---------------------------------------------------------------------------
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// Extent descriptor (T_EXTENT inodes only)
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//
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// Up to MAX_INLINE_EXTENTS are packed into ip->addrs[0..NDIRECT-1].
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// addrs[] = NDIRECT uints = 12*4 = 48 bytes
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// each fsv1_extent = 12 bytes → 48/12 = 4 inline extents
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// (addrs[NDIRECT], [NDIRECT+1], [NDIRECT+2] remain as indirect pointers)
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//
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// For files needing more extents, addrs[NDIRECT] points to an indirect block
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// of BSIZE/sizeof(struct fsv1_extent) = 85 additional extents.
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// ---------------------------------------------------------------------------
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// Renamed from "schfs_extent". The new format in include/schfs.h has its own,
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// completely different, struct of that name -- 64-bit fields and a refcount --
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// and any file including both headers hit a redefinition error. Two structs
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// with one name and two layouts is a trap worth removing rather than working
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// around; this one belongs to the v1 format and dies with it.
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struct fsv1_extent {
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uint start_block; // logical block number in the file (first of run)
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uint start_blkaddr; // physical disk block address
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uint len; // number of contiguous blocks in this run
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};
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// Inline extents packed into addrs[0 .. NDIRECT-1] only.
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#define MAX_INLINE_EXTENTS (NDIRECT * sizeof(uint) / sizeof(struct fsv1_extent))
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// ---------------------------------------------------------------------------
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// On-disk inode (exactly 128 bytes; IPB = 8 inodes per 1024-byte block)
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//
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// Byte layout:
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// 0 short type 2
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// 2 short major 2
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// 4 short minor 2
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// 6 short nlink 2
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// 8 uint size 4
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// 12 uint rwmode 4
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// 16 uint supermode 4
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// 20 uint addrs[15] 60 T_EXTENT: packed fsv1_extent[4] in [0..11], rest normal
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// 80 uint showmode 4
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// 84 uint atime 4 ← last access time (Unix seconds)
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// 88 uint mtime 4 ← last modification time
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// 92 uint ctime 4 ← last metadata-change time
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// 96 uint checksum 4 ← CRC32c (zeroed during computation)
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// 100 uchar pad[28] 28 ← was 44; reduced by 16 for the 4 new fields
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// 128 bytes total
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// ---------------------------------------------------------------------------
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struct dinode {
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short type; // file type
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short major; // major device number (T_DEVICE only)
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short minor; // minor device number (T_DEVICE only)
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short nlink; // hard-link count
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uint size; // file size in bytes
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uint rwmode; // read/write permission flags
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uint supermode; // superuser-only flag
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uint addrs[NDIRECT + 3]; // block addresses / packed extent entries
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uint showmode; // visibility flag
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uint atime; // last access time (seconds since epoch)
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uint mtime; // last modification time
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uint ctime; // last metadata-change time
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uint checksum; // CRC32c of this dinode (field = 0 when hashing)
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uchar pad[28]; // reserved padding (struct = 128 bytes)
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};
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// Inodes per block
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#define IPB (BSIZE / sizeof(struct dinode))
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// Block containing inode i
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#define IBLOCK(i, sb) ((i) / IPB + (sb).inodestart)
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// Bitmap bits per block
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#define BPB (BSIZE * 8)
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// Block of free-block bitmap containing bit for block b
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#define BBLOCK(b, sb) ((b) / BPB + (sb).bmapstart)
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// Block of inode bitmap containing bit for inode i
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#define IBBLOCK(i, sb) ((i) / BPB + (sb).ibmapstart)
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// ---------------------------------------------------------------------------
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// Directory entry
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// ---------------------------------------------------------------------------
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// 30, not 14.
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//
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// 14 was xv6's, and the v1 filesystem truncated to it *silently*: a file called
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// JetBrainsMono-Regular.ttf was stored as "JetBrainsMono-", could not be opened
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// by its real name, and would have collided outright with
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// JetBrainsMono-Bold.ttf. Any two files sharing a 14-character prefix mapped to
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// one entry. That is data loss, not a display limit.
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//
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// The value is chosen so that `struct dirent` is exactly 32 bytes, because the
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// directory HTree below is laid out in *bytes* and a bucket must stay 256 bytes
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// (see DIRENT_BUCKET_BYTES). Going from 16-byte to 32-byte entries therefore
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// halves the slots per bucket from 16 to 8 and changes no offset anywhere else
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// -- HASHRANGE, the overflow region and MAXFSIZE all keep their values. The
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// cost is more overflow use in heavily collided directories, which is a far
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// better trade than silently mangling names.
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//
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// It is still not POSIX's 255. Getting there means reshaping the directory
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// format, which wants the on-disk version policy SchFS is getting first.
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#define DIRSIZ 30
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struct dirent {
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ushort inum;
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char name[DIRSIZ];
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};
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// ---------------------------------------------------------------------------
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// Directory HTree constants
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//
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// BKDRHash(name) returns a value in [16, 16 + HASHRANGE).
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// Each bucket is 256 bytes: 8 dirent slots of 32 bytes. It was 16 slots of 16
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// until DIRSIZ grew; the byte size is what the layout depends on, so it is the
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// thing held constant.
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//
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// With HASHRANGE=443:
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// max primary end byte = (16 + 443) * 256 = 117 504 (~114.75 blocks)
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// OVERFLOW_DIR_START = 113 * BSIZE = 115 712
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// OVERFLOW_DIR_END = 115 * BSIZE = 117 760
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// MAXFSIZE = 119 * BSIZE = 121 856
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// ---------------------------------------------------------------------------
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#define DIRENT_NUM 7168
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#define FIRST_LAYER_NODE_NUM 112
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#define OVERFLOW_BLOCK (FIRST_LAYER_NODE_NUM + 1)
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#define NUM_DIRENT_PER_BLOCK (BSIZE / sizeof(struct dirent))
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#define SECOND_LAYER_NODE_NUM NUM_DIRENT_PER_BLOCK
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#define HASHRANGE 443
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// One hash bucket, in bytes. Every offset in the HTree is derived from this, so
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// it must not change when DIRSIZ does -- see the note on DIRSIZ.
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#define DIRENT_BUCKET_BYTES 256
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#define DIRENT_PER_BUCKET (DIRENT_BUCKET_BYTES / sizeof(struct dirent))
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#define MAXFSIZE (119 * BSIZE)
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// Overflow bucket: shared between fs.c and mkfs.c.
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// These replace the bare "113 * BSIZE" / "115 * BSIZE" literals.
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#define OVERFLOW_DIR_START (113 * BSIZE)
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#define OVERFLOW_DIR_END (115 * BSIZE)
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#endif // FS_H
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