1a505fd66Srsc // File system implementation. Four layers: 2bcca6c6bSrsc // + Blocks: allocator for raw disk blocks. 3bcca6c6bSrsc // + Files: inode allocator, reading, writing, metadata. 4bcca6c6bSrsc // + Directories: inode with special contents (list of other inodes!) 5bcca6c6bSrsc // + Names: paths like /usr/rtm/xv6/fs.c for convenient naming. 6bcca6c6bSrsc // 74d39b633Srsc // Disk layout is: superblock, inodes, block in-use bitmap, data blocks. 8eaea18cbSrsc // 9eaea18cbSrsc // This file contains the low-level file system manipulation 10eaea18cbSrsc // routines. The (higher-level) system call implementations 11eaea18cbSrsc // are in sysfile.c. 12bcca6c6bSrsc 1311a9947fSrtm #include "types.h" 14558ab49fSrsc #include "defs.h" 1511a9947fSrtm #include "param.h" 16558ab49fSrsc #include "stat.h" 1711a9947fSrtm #include "mmu.h" 1811a9947fSrtm #include "proc.h" 1911a9947fSrtm #include "spinlock.h" 2011a9947fSrtm #include "buf.h" 2111a9947fSrtm #include "fs.h" 220aef8914SRuss Cox #include "file.h" 2311a9947fSrtm 24bcca6c6bSrsc #define min(a, b) ((a) < (b) ? (a) : (b)) 25fbf91039Srsc static void itrunc(struct inode*); 2611a9947fSrtm 27a505fd66Srsc // Read the super block. 2813a96baeSFrans Kaashoek void 29a505fd66Srsc readsb(int dev, struct superblock *sb) 30a505fd66Srsc { 31a505fd66Srsc struct buf *bp; 32a505fd66Srsc 33a505fd66Srsc bp = bread(dev, 1); 34a505fd66Srsc memmove(sb, bp->data, sizeof(*sb)); 35a505fd66Srsc brelse(bp); 36a505fd66Srsc } 37a505fd66Srsc 38a505fd66Srsc // Zero a block. 39a505fd66Srsc static void 40a505fd66Srsc bzero(int dev, int bno) 41a505fd66Srsc { 42a505fd66Srsc struct buf *bp; 43a505fd66Srsc 44a505fd66Srsc bp = bread(dev, bno); 45a505fd66Srsc memset(bp->data, 0, BSIZE); 46a505fd66Srsc bwrite(bp); 47a505fd66Srsc brelse(bp); 48a505fd66Srsc } 49a505fd66Srsc 50bcca6c6bSrsc // Blocks. 515be0039cSrtm 52f5527388Srsc // Allocate a disk block. 5324111398Skaashoek static uint 5424111398Skaashoek balloc(uint dev) 5524111398Skaashoek { 56a505fd66Srsc int b, bi, m; 5724111398Skaashoek struct buf *bp; 58a505fd66Srsc struct superblock sb; 5924111398Skaashoek 60a505fd66Srsc bp = 0; 61a505fd66Srsc readsb(dev, &sb); 62a505fd66Srsc for(b = 0; b < sb.size; b += BPB){ 63a505fd66Srsc bp = bread(dev, BBLOCK(b, sb.ninodes)); 6496b7da5fSNickolai Zeldovich for(bi = 0; bi < BPB && bi < (sb.size - b); bi++){ 65a505fd66Srsc m = 1 << (bi % 8); 66a505fd66Srsc if((bp->data[bi/8] & m) == 0){ // Is block free? 67a505fd66Srsc bp->data[bi/8] |= m; // Mark block in use on disk. 6813a96baeSFrans Kaashoek log_write(bp); 6924111398Skaashoek brelse(bp); 70a505fd66Srsc return b + bi; 7124111398Skaashoek } 72a505fd66Srsc } 7328d9ef04Skaashoek brelse(bp); 747d4aef6cSrsc } 757d4aef6cSrsc panic("balloc: out of blocks"); 767d4aef6cSrsc } 7724111398Skaashoek 78bb207a1dSrsc // Free a disk block. 7928d9ef04Skaashoek static void 8028d9ef04Skaashoek bfree(int dev, uint b) 8128d9ef04Skaashoek { 8228d9ef04Skaashoek struct buf *bp; 83a505fd66Srsc struct superblock sb; 84a505fd66Srsc int bi, m; 8528d9ef04Skaashoek 86a505fd66Srsc bzero(dev, b); 8728d9ef04Skaashoek 88a505fd66Srsc readsb(dev, &sb); 89a505fd66Srsc bp = bread(dev, BBLOCK(b, sb.ninodes)); 9028d9ef04Skaashoek bi = b % BPB; 91a505fd66Srsc m = 1 << (bi % 8); 92902b13f5Srtm if((bp->data[bi/8] & m) == 0) 93902b13f5Srtm panic("freeing free block"); 94a505fd66Srsc bp->data[bi/8] &= ~m; // Mark block free on disk. 9513a96baeSFrans Kaashoek log_write(bp); 9628d9ef04Skaashoek brelse(bp); 9728d9ef04Skaashoek } 9824111398Skaashoek 996c34f97cSrsc // Inodes. 1006c34f97cSrsc // 1016c34f97cSrsc // An inode is a single, unnamed file in the file system. 1026c34f97cSrsc // The inode disk structure holds metadata (the type, device numbers, 1036c34f97cSrsc // and data size) along with a list of blocks where the associated 1046c34f97cSrsc // data can be found. 105bcca6c6bSrsc // 106bcca6c6bSrsc // The inodes are laid out sequentially on disk immediately after 107bcca6c6bSrsc // the superblock. The kernel keeps a cache of the in-use 108bcca6c6bSrsc // on-disk structures to provide a place for synchronizing access 109bcca6c6bSrsc // to inodes shared between multiple processes. 110bcca6c6bSrsc // 111902b13f5Srtm // ip->ref counts the number of pointer references to this cached 11248755214SRuss Cox // inode; references are typically kept in struct file and in proc->cwd. 113bcca6c6bSrsc // When ip->ref falls to zero, the inode is no longer cached. 114bcca6c6bSrsc // It is an error to use an inode without holding a reference to it. 115bcca6c6bSrsc // 116eaea18cbSrsc // Processes are only allowed to read and write inode 1176c34f97cSrsc // metadata and contents when holding the inode's lock, 1186c34f97cSrsc // represented by the I_BUSY flag in the in-memory copy. 119902b13f5Srtm // Because inode locks are held during disk accesses, 120902b13f5Srtm // they are implemented using a flag rather than with 121902b13f5Srtm // spin locks. Callers are responsible for locking 122eaea18cbSrsc // inodes before passing them to routines in this file; leaving 123eaea18cbSrsc // this responsibility with the caller makes it possible for them 124eaea18cbSrsc // to create arbitrarily-sized atomic operations. 125eaea18cbSrsc // 126eaea18cbSrsc // To give maximum control over locking to the callers, 127eaea18cbSrsc // the routines in this file that return inode pointers 128eaea18cbSrsc // return pointers to *unlocked* inodes. It is the callers' 129902b13f5Srtm // responsibility to lock them before using them. A non-zero 130902b13f5Srtm // ip->ref keeps these unlocked inodes in the cache. 131bcca6c6bSrsc 132bcca6c6bSrsc struct { 133bcca6c6bSrsc struct spinlock lock; 134bcca6c6bSrsc struct inode inode[NINODE]; 135bcca6c6bSrsc } icache; 136bcca6c6bSrsc 137bcca6c6bSrsc void 138bcca6c6bSrsc iinit(void) 139bcca6c6bSrsc { 14034295f46Srsc initlock(&icache.lock, "icache"); 141bcca6c6bSrsc } 142bcca6c6bSrsc 143f9a06440SRuss Cox static struct inode* iget(uint dev, uint inum); 144f9a06440SRuss Cox 145f9a06440SRuss Cox //PAGEBREAK! 146f9a06440SRuss Cox // Allocate a new inode with the given type on device dev. 147f9a06440SRuss Cox struct inode* 148f9a06440SRuss Cox ialloc(uint dev, short type) 149f9a06440SRuss Cox { 150f9a06440SRuss Cox int inum; 151f9a06440SRuss Cox struct buf *bp; 152f9a06440SRuss Cox struct dinode *dip; 153f9a06440SRuss Cox struct superblock sb; 154f9a06440SRuss Cox 155f9a06440SRuss Cox readsb(dev, &sb); 156f9a06440SRuss Cox for(inum = 1; inum < sb.ninodes; inum++){ // loop over inode blocks 157f9a06440SRuss Cox bp = bread(dev, IBLOCK(inum)); 158f9a06440SRuss Cox dip = (struct dinode*)bp->data + inum%IPB; 159f9a06440SRuss Cox if(dip->type == 0){ // a free inode 160f9a06440SRuss Cox memset(dip, 0, sizeof(*dip)); 161f9a06440SRuss Cox dip->type = type; 16213a96baeSFrans Kaashoek log_write(bp); // mark it allocated on the disk 163f9a06440SRuss Cox brelse(bp); 164f9a06440SRuss Cox return iget(dev, inum); 165f9a06440SRuss Cox } 166f9a06440SRuss Cox brelse(bp); 167f9a06440SRuss Cox } 168f9a06440SRuss Cox panic("ialloc: no inodes"); 169f9a06440SRuss Cox } 170f9a06440SRuss Cox 171f9a06440SRuss Cox // Copy inode, which has changed, from memory to disk. 172f9a06440SRuss Cox void 173f9a06440SRuss Cox iupdate(struct inode *ip) 174f9a06440SRuss Cox { 175f9a06440SRuss Cox struct buf *bp; 176f9a06440SRuss Cox struct dinode *dip; 177f9a06440SRuss Cox 178f9a06440SRuss Cox bp = bread(ip->dev, IBLOCK(ip->inum)); 179f9a06440SRuss Cox dip = (struct dinode*)bp->data + ip->inum%IPB; 180f9a06440SRuss Cox dip->type = ip->type; 181f9a06440SRuss Cox dip->major = ip->major; 182f9a06440SRuss Cox dip->minor = ip->minor; 183f9a06440SRuss Cox dip->nlink = ip->nlink; 184f9a06440SRuss Cox dip->size = ip->size; 185f9a06440SRuss Cox memmove(dip->addrs, ip->addrs, sizeof(ip->addrs)); 18613a96baeSFrans Kaashoek log_write(bp); 187f9a06440SRuss Cox brelse(bp); 188f9a06440SRuss Cox } 189f9a06440SRuss Cox 190f5527388Srsc // Find the inode with number inum on device dev 1917895178dSrsc // and return the in-memory copy. 19207090dd7Srsc static struct inode* 19311a9947fSrtm iget(uint dev, uint inum) 19411a9947fSrtm { 195bcca6c6bSrsc struct inode *ip, *empty; 19611a9947fSrtm 197bcca6c6bSrsc acquire(&icache.lock); 19811a9947fSrtm 199bcca6c6bSrsc // Try for cached inode. 200bcca6c6bSrsc empty = 0; 201bcca6c6bSrsc for(ip = &icache.inode[0]; ip < &icache.inode[NINODE]; ip++){ 2020d6bbd31Srsc if(ip->ref > 0 && ip->dev == dev && ip->inum == inum){ 2030d6bbd31Srsc ip->ref++; 204bcca6c6bSrsc release(&icache.lock); 20507090dd7Srsc return ip; 20611a9947fSrtm } 207bcca6c6bSrsc if(empty == 0 && ip->ref == 0) // Remember empty slot. 208bcca6c6bSrsc empty = ip; 20911a9947fSrtm } 21011a9947fSrtm 211bcca6c6bSrsc // Allocate fresh inode. 212bcca6c6bSrsc if(empty == 0) 21332eea766Srsc panic("iget: no inodes"); 21411a9947fSrtm 215bcca6c6bSrsc ip = empty; 216bcca6c6bSrsc ip->dev = dev; 217bcca6c6bSrsc ip->inum = inum; 218bcca6c6bSrsc ip->ref = 1; 219f32f3638Srsc ip->flags = 0; 220bcca6c6bSrsc release(&icache.lock); 22111a9947fSrtm 22207090dd7Srsc return ip; 223f32f3638Srsc } 224f32f3638Srsc 225eaea18cbSrsc // Increment reference count for ip. 226eaea18cbSrsc // Returns ip to enable ip = idup(ip1) idiom. 22707090dd7Srsc struct inode* 22807090dd7Srsc idup(struct inode *ip) 229f32f3638Srsc { 230eaea18cbSrsc acquire(&icache.lock); 231eaea18cbSrsc ip->ref++; 232eaea18cbSrsc release(&icache.lock); 23307090dd7Srsc return ip; 234f32f3638Srsc } 235f32f3638Srsc 236f32f3638Srsc // Lock the given inode. 23707090dd7Srsc void 23807090dd7Srsc ilock(struct inode *ip) 239f32f3638Srsc { 240f32f3638Srsc struct buf *bp; 241f32f3638Srsc struct dinode *dip; 242eaea18cbSrsc 24307090dd7Srsc if(ip == 0 || ip->ref < 1) 24407090dd7Srsc panic("ilock"); 245f32f3638Srsc 246f32f3638Srsc acquire(&icache.lock); 247f32f3638Srsc while(ip->flags & I_BUSY) 248f32f3638Srsc sleep(ip, &icache.lock); 249f32f3638Srsc ip->flags |= I_BUSY; 250f32f3638Srsc release(&icache.lock); 251f32f3638Srsc 252f32f3638Srsc if(!(ip->flags & I_VALID)){ 253f32f3638Srsc bp = bread(ip->dev, IBLOCK(ip->inum)); 2543341e30fSrsc dip = (struct dinode*)bp->data + ip->inum%IPB; 255bcca6c6bSrsc ip->type = dip->type; 256bcca6c6bSrsc ip->major = dip->major; 257bcca6c6bSrsc ip->minor = dip->minor; 258bcca6c6bSrsc ip->nlink = dip->nlink; 259bcca6c6bSrsc ip->size = dip->size; 260bcca6c6bSrsc memmove(ip->addrs, dip->addrs, sizeof(ip->addrs)); 26111a9947fSrtm brelse(bp); 262f32f3638Srsc ip->flags |= I_VALID; 263eaea18cbSrsc if(ip->type == 0) 264eaea18cbSrsc panic("ilock: no type"); 26511a9947fSrtm } 266bcca6c6bSrsc } 267bcca6c6bSrsc 268bcca6c6bSrsc // Unlock the given inode. 26907090dd7Srsc void 270bcca6c6bSrsc iunlock(struct inode *ip) 271bcca6c6bSrsc { 27207090dd7Srsc if(ip == 0 || !(ip->flags & I_BUSY) || ip->ref < 1) 273bcca6c6bSrsc panic("iunlock"); 274bcca6c6bSrsc 275bcca6c6bSrsc acquire(&icache.lock); 276ce72cadbSrsc ip->flags &= ~I_BUSY; 277bcca6c6bSrsc wakeup(ip); 278bcca6c6bSrsc release(&icache.lock); 279bcca6c6bSrsc } 280bcca6c6bSrsc 281f32f3638Srsc // Caller holds reference to unlocked ip. Drop reference. 282bcca6c6bSrsc void 28307090dd7Srsc iput(struct inode *ip) 284bcca6c6bSrsc { 285f32f3638Srsc acquire(&icache.lock); 286f32f3638Srsc if(ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0){ 287f32f3638Srsc // inode is no longer used: truncate and free inode. 288f32f3638Srsc if(ip->flags & I_BUSY) 289eaea18cbSrsc panic("iput busy"); 290f32f3638Srsc ip->flags |= I_BUSY; 291f32f3638Srsc release(&icache.lock); 292f32f3638Srsc itrunc(ip); 293f32f3638Srsc ip->type = 0; 294f32f3638Srsc iupdate(ip); 295f32f3638Srsc acquire(&icache.lock); 296ce72cadbSrsc ip->flags = 0; 2978970df0cSrsc wakeup(ip); 298f32f3638Srsc } 299f32f3638Srsc ip->ref--; 300f32f3638Srsc release(&icache.lock); 301bcca6c6bSrsc } 302bcca6c6bSrsc 3037895178dSrsc // Common idiom: unlock, then put. 30407090dd7Srsc void 30507090dd7Srsc iunlockput(struct inode *ip) 30607090dd7Srsc { 30707090dd7Srsc iunlock(ip); 30807090dd7Srsc iput(ip); 30907090dd7Srsc } 31007090dd7Srsc 3118d2e9a48Srsc //PAGEBREAK! 312bcca6c6bSrsc // Inode contents 313bcca6c6bSrsc // 314bcca6c6bSrsc // The contents (data) associated with each inode is stored 315bcca6c6bSrsc // in a sequence of blocks on the disk. The first NDIRECT blocks 3167895178dSrsc // are listed in ip->addrs[]. The next NINDIRECT blocks are 317745e73cdSAustin Clements // listed in the block ip->addrs[NDIRECT]. 3189d3fb671Srtm 319bb207a1dSrsc // Return the disk block address of the nth block in inode ip. 32013ae8808Srsc // If there is no such block, bmap allocates one. 321eaea18cbSrsc static uint 32213ae8808Srsc bmap(struct inode *ip, uint bn) 32322bac2cbSkaashoek { 324bcca6c6bSrsc uint addr, *a; 325bcca6c6bSrsc struct buf *bp; 32622bac2cbSkaashoek 327ea2909b6Skaashoek if(bn < NDIRECT){ 32813ae8808Srsc if((addr = ip->addrs[bn]) == 0) 329bcca6c6bSrsc ip->addrs[bn] = addr = balloc(ip->dev); 330bcca6c6bSrsc return addr; 331bcca6c6bSrsc } 332bcca6c6bSrsc bn -= NDIRECT; 333bcca6c6bSrsc 334bcca6c6bSrsc if(bn < NINDIRECT){ 335bcca6c6bSrsc // Load indirect block, allocating if necessary. 33613ae8808Srsc if((addr = ip->addrs[NDIRECT]) == 0) 337ba6cd8a6Srsc ip->addrs[NDIRECT] = addr = balloc(ip->dev); 338bcca6c6bSrsc bp = bread(ip->dev, addr); 339bcca6c6bSrsc a = (uint*)bp->data; 340bcca6c6bSrsc if((addr = a[bn]) == 0){ 341bcca6c6bSrsc a[bn] = addr = balloc(ip->dev); 34213a96baeSFrans Kaashoek log_write(bp); 343bcca6c6bSrsc } 344bcca6c6bSrsc brelse(bp); 345bcca6c6bSrsc return addr; 34622bac2cbSkaashoek } 34722bac2cbSkaashoek 348bcca6c6bSrsc panic("bmap: out of range"); 349bcca6c6bSrsc } 350bcca6c6bSrsc 351bcca6c6bSrsc // Truncate inode (discard contents). 3528eb20827Srtm // Only called after the last dirent referring 3538eb20827Srtm // to this inode has been erased on disk. 354fbf91039Srsc static void 3552aa4c3bcSrtm itrunc(struct inode *ip) 35622bac2cbSkaashoek { 357ea2909b6Skaashoek int i, j; 358bcca6c6bSrsc struct buf *bp; 3597d4aef6cSrsc uint *a; 36022bac2cbSkaashoek 361bcca6c6bSrsc for(i = 0; i < NDIRECT; i++){ 362bcca6c6bSrsc if(ip->addrs[i]){ 36322bac2cbSkaashoek bfree(ip->dev, ip->addrs[i]); 36422bac2cbSkaashoek ip->addrs[i] = 0; 36522bac2cbSkaashoek } 36622bac2cbSkaashoek } 367bcca6c6bSrsc 368ba6cd8a6Srsc if(ip->addrs[NDIRECT]){ 369ba6cd8a6Srsc bp = bread(ip->dev, ip->addrs[NDIRECT]); 370bcca6c6bSrsc a = (uint*)bp->data; 371bcca6c6bSrsc for(j = 0; j < NINDIRECT; j++){ 372bcca6c6bSrsc if(a[j]) 373bcca6c6bSrsc bfree(ip->dev, a[j]); 374bcca6c6bSrsc } 375bcca6c6bSrsc brelse(bp); 376ba6cd8a6Srsc bfree(ip->dev, ip->addrs[NDIRECT]); 377ba6cd8a6Srsc ip->addrs[NDIRECT] = 0; 378bcca6c6bSrsc } 379bcca6c6bSrsc 38022bac2cbSkaashoek ip->size = 0; 38122bac2cbSkaashoek iupdate(ip); 38222bac2cbSkaashoek } 38322bac2cbSkaashoek 384bb207a1dSrsc // Copy stat information from inode. 385e958c538Skaashoek void 3861f544842Skaashoek stati(struct inode *ip, struct stat *st) 3871f544842Skaashoek { 3881dca3afbSrsc st->dev = ip->dev; 3891dca3afbSrsc st->ino = ip->inum; 3901dca3afbSrsc st->type = ip->type; 3911dca3afbSrsc st->nlink = ip->nlink; 3921dca3afbSrsc st->size = ip->size; 3931f544842Skaashoek } 3941f544842Skaashoek 395eaea18cbSrsc //PAGEBREAK! 396bb207a1dSrsc // Read data from inode. 397c59361f1Srtm int 39817a85657Srtm readi(struct inode *ip, char *dst, uint off, uint n) 399c59361f1Srtm { 400bcca6c6bSrsc uint tot, m; 401c59361f1Srtm struct buf *bp; 402c59361f1Srtm 403939f9edeSkaashoek if(ip->type == T_DEV){ 4041dca3afbSrsc if(ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].read) 405939f9edeSkaashoek return -1; 406d844f0f9Srsc return devsw[ip->major].read(ip, dst, n); 407939f9edeSkaashoek } 408939f9edeSkaashoek 4097895178dSrsc if(off > ip->size || off + n < off) 410bcca6c6bSrsc return -1; 411bcca6c6bSrsc if(off + n > ip->size) 412bcca6c6bSrsc n = ip->size - off; 413bcca6c6bSrsc 414bcca6c6bSrsc for(tot=0; tot<n; tot+=m, off+=m, dst+=m){ 41513ae8808Srsc bp = bread(ip->dev, bmap(ip, off/BSIZE)); 416bcca6c6bSrsc m = min(n - tot, BSIZE - off%BSIZE); 417bcca6c6bSrsc memmove(dst, bp->data + off%BSIZE, m); 418c59361f1Srtm brelse(bp); 419c59361f1Srtm } 420bcca6c6bSrsc return n; 421ea2909b6Skaashoek } 422ea2909b6Skaashoek 423eaea18cbSrsc // PAGEBREAK! 424bb207a1dSrsc // Write data to inode. 425ea2909b6Skaashoek int 426bcca6c6bSrsc writei(struct inode *ip, char *src, uint off, uint n) 4276fa5ffb5Skaashoek { 428bcca6c6bSrsc uint tot, m; 4297d4aef6cSrsc struct buf *bp; 4307d4aef6cSrsc 4316fa5ffb5Skaashoek if(ip->type == T_DEV){ 4321dca3afbSrsc if(ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].write) 433939f9edeSkaashoek return -1; 434d844f0f9Srsc return devsw[ip->major].write(ip, src, n); 4357d4aef6cSrsc } 4367d4aef6cSrsc 43713ae8808Srsc if(off > ip->size || off + n < off) 438bcca6c6bSrsc return -1; 439bcca6c6bSrsc if(off + n > MAXFILE*BSIZE) 440*2e590463SRobert Morris return -1; 441bcca6c6bSrsc 442bcca6c6bSrsc for(tot=0; tot<n; tot+=m, off+=m, src+=m){ 44313ae8808Srsc bp = bread(ip->dev, bmap(ip, off/BSIZE)); 444bcca6c6bSrsc m = min(n - tot, BSIZE - off%BSIZE); 445bcca6c6bSrsc memmove(bp->data + off%BSIZE, src, m); 446*2e590463SRobert Morris log_write(bp); 44728d9ef04Skaashoek brelse(bp); 44828d9ef04Skaashoek } 449bcca6c6bSrsc 450bcca6c6bSrsc if(n > 0 && off > ip->size){ 45148b82470Srsc ip->size = off; 45228d9ef04Skaashoek iupdate(ip); 45328d9ef04Skaashoek } 454bcca6c6bSrsc return n; 4556fa5ffb5Skaashoek } 4566fa5ffb5Skaashoek 457eaea18cbSrsc //PAGEBREAK! 458bcca6c6bSrsc // Directories 459bcca6c6bSrsc 460eaea18cbSrsc int 461fbf91039Srsc namecmp(const char *s, const char *t) 462fbf91039Srsc { 463766ba5ccSrsc return strncmp(s, t, DIRSIZ); 464fbf91039Srsc } 465fbf91039Srsc 466bcca6c6bSrsc // Look for a directory entry in a directory. 467eaea18cbSrsc // If found, set *poff to byte offset of entry. 46820365348Srtm // Caller must have already locked dp. 46907090dd7Srsc struct inode* 470fbf91039Srsc dirlookup(struct inode *dp, char *name, uint *poff) 471bcca6c6bSrsc { 472f32f3638Srsc uint off, inum; 473bcca6c6bSrsc struct buf *bp; 474bcca6c6bSrsc struct dirent *de; 475bcca6c6bSrsc 476bcca6c6bSrsc if(dp->type != T_DIR) 47720365348Srtm panic("dirlookup not DIR"); 478bcca6c6bSrsc 479bcca6c6bSrsc for(off = 0; off < dp->size; off += BSIZE){ 48013ae8808Srsc bp = bread(dp->dev, bmap(dp, off / BSIZE)); 481bcca6c6bSrsc for(de = (struct dirent*)bp->data; 482bcca6c6bSrsc de < (struct dirent*)(bp->data + BSIZE); 483bcca6c6bSrsc de++){ 484bcca6c6bSrsc if(de->inum == 0) 485bcca6c6bSrsc continue; 486fbf91039Srsc if(namecmp(name, de->name) == 0){ 487bcca6c6bSrsc // entry matches path element 488e2a620daSrsc if(poff) 489bcca6c6bSrsc *poff = off + (uchar*)de - bp->data; 490f32f3638Srsc inum = de->inum; 491bcca6c6bSrsc brelse(bp); 492f32f3638Srsc return iget(dp->dev, inum); 493f32f3638Srsc } 494f32f3638Srsc } 495f32f3638Srsc brelse(bp); 496f32f3638Srsc } 497bcca6c6bSrsc return 0; 498bcca6c6bSrsc } 499bcca6c6bSrsc 50013ae8808Srsc // Write a new directory entry (name, inum) into the directory dp. 501eaea18cbSrsc int 50213ae8808Srsc dirlink(struct inode *dp, char *name, uint inum) 503bcca6c6bSrsc { 504e2a620daSrsc int off; 505bcca6c6bSrsc struct dirent de; 50607090dd7Srsc struct inode *ip; 507f32f3638Srsc 508eaea18cbSrsc // Check that name is not present. 50907090dd7Srsc if((ip = dirlookup(dp, name, 0)) != 0){ 51007090dd7Srsc iput(ip); 511f32f3638Srsc return -1; 512f32f3638Srsc } 513bcca6c6bSrsc 514bcca6c6bSrsc // Look for an empty dirent. 515bcca6c6bSrsc for(off = 0; off < dp->size; off += sizeof(de)){ 516bcca6c6bSrsc if(readi(dp, (char*)&de, off, sizeof(de)) != sizeof(de)) 5177895178dSrsc panic("dirlink read"); 518bcca6c6bSrsc if(de.inum == 0) 519bcca6c6bSrsc break; 520bcca6c6bSrsc } 521bcca6c6bSrsc 522766ba5ccSrsc strncpy(de.name, name, DIRSIZ); 52313ae8808Srsc de.inum = inum; 524bcca6c6bSrsc if(writei(dp, (char*)&de, off, sizeof(de)) != sizeof(de)) 5257895178dSrsc panic("dirlink"); 526f32f3638Srsc 527f32f3638Srsc return 0; 528bcca6c6bSrsc } 529bcca6c6bSrsc 5308d2e9a48Srsc //PAGEBREAK! 531bcca6c6bSrsc // Paths 532bcca6c6bSrsc 533eaea18cbSrsc // Copy the next path element from path into name. 534eaea18cbSrsc // Return a pointer to the element following the copied one. 535eaea18cbSrsc // The returned path has no leading slashes, 536eaea18cbSrsc // so the caller can check *path=='\0' to see if the name is the last one. 537eaea18cbSrsc // If no name to remove, return 0. 538ab5c2dbbSrsc // 539ab5c2dbbSrsc // Examples: 540eaea18cbSrsc // skipelem("a/bb/c", name) = "bb/c", setting name = "a" 5417895178dSrsc // skipelem("///a//bb", name) = "bb", setting name = "a" 54213ae8808Srsc // skipelem("a", name) = "", setting name = "a" 543eaea18cbSrsc // skipelem("", name) = skipelem("////", name) = 0 544ab5c2dbbSrsc // 545ab5c2dbbSrsc static char* 546fbf91039Srsc skipelem(char *path, char *name) 547ab5c2dbbSrsc { 548fbf91039Srsc char *s; 549fbf91039Srsc int len; 550fbf91039Srsc 551ab5c2dbbSrsc while(*path == '/') 552ab5c2dbbSrsc path++; 553ab5c2dbbSrsc if(*path == 0) 554ab5c2dbbSrsc return 0; 555fbf91039Srsc s = path; 556ab5c2dbbSrsc while(*path != '/' && *path != 0) 557ab5c2dbbSrsc path++; 558fbf91039Srsc len = path - s; 559fbf91039Srsc if(len >= DIRSIZ) 560fbf91039Srsc memmove(name, s, DIRSIZ); 561fbf91039Srsc else { 562fbf91039Srsc memmove(name, s, len); 563fbf91039Srsc name[len] = 0; 564fbf91039Srsc } 565ab5c2dbbSrsc while(*path == '/') 566ab5c2dbbSrsc path++; 567ab5c2dbbSrsc return path; 568ab5c2dbbSrsc } 569ab5c2dbbSrsc 570eaea18cbSrsc // Look up and return the inode for a path name. 571bf2932a6Srsc // If parent != 0, return the inode for the parent and copy the final 572bf2932a6Srsc // path element into name, which must have room for DIRSIZ bytes. 57307090dd7Srsc static struct inode* 574f9a06440SRuss Cox namex(char *path, int nameiparent, char *name) 5759d3fb671Srtm { 57607090dd7Srsc struct inode *ip, *next; 5779d3fb671Srtm 578ab5c2dbbSrsc if(*path == '/') 5792ce40d70Srtm ip = iget(ROOTDEV, ROOTINO); 580f32f3638Srsc else 58148755214SRuss Cox ip = idup(proc->cwd); 5829d3fb671Srtm 583fbf91039Srsc while((path = skipelem(path, name)) != 0){ 58407090dd7Srsc ilock(ip); 58507090dd7Srsc if(ip->type != T_DIR){ 58607090dd7Srsc iunlockput(ip); 587eaea18cbSrsc return 0; 588eaea18cbSrsc } 589f9a06440SRuss Cox if(nameiparent && *path == '\0'){ 590e2a620daSrsc // Stop one level early. 59107090dd7Srsc iunlock(ip); 59207090dd7Srsc return ip; 593ab5c2dbbSrsc } 5947895178dSrsc if((next = dirlookup(ip, name, 0)) == 0){ 59507090dd7Srsc iunlockput(ip); 596eaea18cbSrsc return 0; 597eaea18cbSrsc } 59807090dd7Srsc iunlockput(ip); 59907090dd7Srsc ip = next; 600ab5c2dbbSrsc } 601f9a06440SRuss Cox if(nameiparent){ 60207090dd7Srsc iput(ip); 6035051da6dSrtm return 0; 60420365348Srtm } 60507090dd7Srsc return ip; 6060633b971Skaashoek } 6079d3fb671Srtm 6087895178dSrsc struct inode* 6097895178dSrsc namei(char *path) 6107895178dSrsc { 6117895178dSrsc char name[DIRSIZ]; 61213ae8808Srsc return namex(path, 0, name); 6137895178dSrsc } 614bf2932a6Srsc 6157895178dSrsc struct inode* 6167895178dSrsc nameiparent(char *path, char *name) 6177895178dSrsc { 61813ae8808Srsc return namex(path, 1, name); 6197895178dSrsc } 620