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" 2211a9947fSrtm #include "fsvar.h" 236fa5ffb5Skaashoek #include "dev.h" 2411a9947fSrtm 25bcca6c6bSrsc #define min(a, b) ((a) < (b) ? (a) : (b)) 26fbf91039Srsc static void itrunc(struct inode*); 2711a9947fSrtm 28a505fd66Srsc // Read the super block. 29a505fd66Srsc static void 30a505fd66Srsc readsb(int dev, struct superblock *sb) 31a505fd66Srsc { 32a505fd66Srsc struct buf *bp; 33a505fd66Srsc 34a505fd66Srsc bp = bread(dev, 1); 35a505fd66Srsc memmove(sb, bp->data, sizeof(*sb)); 36a505fd66Srsc brelse(bp); 37a505fd66Srsc } 38a505fd66Srsc 39a505fd66Srsc // Zero a block. 40a505fd66Srsc static void 41a505fd66Srsc bzero(int dev, int bno) 42a505fd66Srsc { 43a505fd66Srsc struct buf *bp; 44a505fd66Srsc 45a505fd66Srsc bp = bread(dev, bno); 46a505fd66Srsc memset(bp->data, 0, BSIZE); 47a505fd66Srsc bwrite(bp); 48a505fd66Srsc brelse(bp); 49a505fd66Srsc } 50a505fd66Srsc 51bcca6c6bSrsc // Blocks. 525be0039cSrtm 53f5527388Srsc // Allocate a disk block. 5424111398Skaashoek static uint 5524111398Skaashoek balloc(uint dev) 5624111398Skaashoek { 57a505fd66Srsc int b, bi, m; 5824111398Skaashoek struct buf *bp; 59a505fd66Srsc struct superblock sb; 6024111398Skaashoek 61a505fd66Srsc bp = 0; 62a505fd66Srsc readsb(dev, &sb); 63a505fd66Srsc for(b = 0; b < sb.size; b += BPB){ 64a505fd66Srsc bp = bread(dev, BBLOCK(b, sb.ninodes)); 65a505fd66Srsc for(bi = 0; bi < BPB; bi++){ 66a505fd66Srsc m = 1 << (bi % 8); 67a505fd66Srsc if((bp->data[bi/8] & m) == 0){ // Is block free? 68a505fd66Srsc bp->data[bi/8] |= m; // Mark block in use on disk. 69a505fd66Srsc bwrite(bp); 7024111398Skaashoek brelse(bp); 71a505fd66Srsc return b + bi; 7224111398Skaashoek } 73a505fd66Srsc } 7428d9ef04Skaashoek brelse(bp); 757d4aef6cSrsc } 767d4aef6cSrsc panic("balloc: out of blocks"); 777d4aef6cSrsc } 7824111398Skaashoek 79bb207a1dSrsc // Free a disk block. 8028d9ef04Skaashoek static void 8128d9ef04Skaashoek bfree(int dev, uint b) 8228d9ef04Skaashoek { 8328d9ef04Skaashoek struct buf *bp; 84a505fd66Srsc struct superblock sb; 85a505fd66Srsc int bi, m; 8628d9ef04Skaashoek 87a505fd66Srsc bzero(dev, b); 8828d9ef04Skaashoek 89a505fd66Srsc readsb(dev, &sb); 90a505fd66Srsc bp = bread(dev, BBLOCK(b, sb.ninodes)); 9128d9ef04Skaashoek bi = b % BPB; 92a505fd66Srsc m = 1 << (bi % 8); 93902b13f5Srtm if((bp->data[bi/8] & m) == 0) 94902b13f5Srtm panic("freeing free block"); 95a505fd66Srsc bp->data[bi/8] &= ~m; // Mark block free on disk. 96a505fd66Srsc bwrite(bp); 9728d9ef04Skaashoek brelse(bp); 9828d9ef04Skaashoek } 9924111398Skaashoek 1006c34f97cSrsc // Inodes. 1016c34f97cSrsc // 1026c34f97cSrsc // An inode is a single, unnamed file in the file system. 1036c34f97cSrsc // The inode disk structure holds metadata (the type, device numbers, 1046c34f97cSrsc // and data size) along with a list of blocks where the associated 1056c34f97cSrsc // data can be found. 106bcca6c6bSrsc // 107bcca6c6bSrsc // The inodes are laid out sequentially on disk immediately after 108bcca6c6bSrsc // the superblock. The kernel keeps a cache of the in-use 109bcca6c6bSrsc // on-disk structures to provide a place for synchronizing access 110bcca6c6bSrsc // to inodes shared between multiple processes. 111bcca6c6bSrsc // 112902b13f5Srtm // ip->ref counts the number of pointer references to this cached 113bcca6c6bSrsc // inode; references are typically kept in struct file and in cp->cwd. 114bcca6c6bSrsc // When ip->ref falls to zero, the inode is no longer cached. 115bcca6c6bSrsc // It is an error to use an inode without holding a reference to it. 116bcca6c6bSrsc // 117eaea18cbSrsc // Processes are only allowed to read and write inode 1186c34f97cSrsc // metadata and contents when holding the inode's lock, 1196c34f97cSrsc // represented by the I_BUSY flag in the in-memory copy. 120902b13f5Srtm // Because inode locks are held during disk accesses, 121902b13f5Srtm // they are implemented using a flag rather than with 122902b13f5Srtm // spin locks. Callers are responsible for locking 123eaea18cbSrsc // inodes before passing them to routines in this file; leaving 124eaea18cbSrsc // this responsibility with the caller makes it possible for them 125eaea18cbSrsc // to create arbitrarily-sized atomic operations. 126eaea18cbSrsc // 127eaea18cbSrsc // To give maximum control over locking to the callers, 128eaea18cbSrsc // the routines in this file that return inode pointers 129eaea18cbSrsc // return pointers to *unlocked* inodes. It is the callers' 130902b13f5Srtm // responsibility to lock them before using them. A non-zero 131902b13f5Srtm // ip->ref keeps these unlocked inodes in the cache. 132bcca6c6bSrsc 133bcca6c6bSrsc struct { 134bcca6c6bSrsc struct spinlock lock; 135bcca6c6bSrsc struct inode inode[NINODE]; 136bcca6c6bSrsc } icache; 137bcca6c6bSrsc 138bcca6c6bSrsc void 139bcca6c6bSrsc iinit(void) 140bcca6c6bSrsc { 14134295f46Srsc initlock(&icache.lock, "icache"); 142bcca6c6bSrsc } 143bcca6c6bSrsc 144*f9a06440SRuss Cox static struct inode* iget(uint dev, uint inum); 145*f9a06440SRuss Cox 146*f9a06440SRuss Cox //PAGEBREAK! 147*f9a06440SRuss Cox // Allocate a new inode with the given type on device dev. 148*f9a06440SRuss Cox struct inode* 149*f9a06440SRuss Cox ialloc(uint dev, short type) 150*f9a06440SRuss Cox { 151*f9a06440SRuss Cox int inum; 152*f9a06440SRuss Cox struct buf *bp; 153*f9a06440SRuss Cox struct dinode *dip; 154*f9a06440SRuss Cox struct superblock sb; 155*f9a06440SRuss Cox 156*f9a06440SRuss Cox readsb(dev, &sb); 157*f9a06440SRuss Cox for(inum = 1; inum < sb.ninodes; inum++){ // loop over inode blocks 158*f9a06440SRuss Cox bp = bread(dev, IBLOCK(inum)); 159*f9a06440SRuss Cox dip = (struct dinode*)bp->data + inum%IPB; 160*f9a06440SRuss Cox if(dip->type == 0){ // a free inode 161*f9a06440SRuss Cox memset(dip, 0, sizeof(*dip)); 162*f9a06440SRuss Cox dip->type = type; 163*f9a06440SRuss Cox bwrite(bp); // mark it allocated on the disk 164*f9a06440SRuss Cox brelse(bp); 165*f9a06440SRuss Cox return iget(dev, inum); 166*f9a06440SRuss Cox } 167*f9a06440SRuss Cox brelse(bp); 168*f9a06440SRuss Cox } 169*f9a06440SRuss Cox panic("ialloc: no inodes"); 170*f9a06440SRuss Cox } 171*f9a06440SRuss Cox 172*f9a06440SRuss Cox // Copy inode, which has changed, from memory to disk. 173*f9a06440SRuss Cox void 174*f9a06440SRuss Cox iupdate(struct inode *ip) 175*f9a06440SRuss Cox { 176*f9a06440SRuss Cox struct buf *bp; 177*f9a06440SRuss Cox struct dinode *dip; 178*f9a06440SRuss Cox 179*f9a06440SRuss Cox bp = bread(ip->dev, IBLOCK(ip->inum)); 180*f9a06440SRuss Cox dip = (struct dinode*)bp->data + ip->inum%IPB; 181*f9a06440SRuss Cox dip->type = ip->type; 182*f9a06440SRuss Cox dip->major = ip->major; 183*f9a06440SRuss Cox dip->minor = ip->minor; 184*f9a06440SRuss Cox dip->nlink = ip->nlink; 185*f9a06440SRuss Cox dip->size = ip->size; 186*f9a06440SRuss Cox memmove(dip->addrs, ip->addrs, sizeof(ip->addrs)); 187*f9a06440SRuss Cox bwrite(bp); 188*f9a06440SRuss Cox brelse(bp); 189*f9a06440SRuss Cox } 190*f9a06440SRuss Cox 191f5527388Srsc // Find the inode with number inum on device dev 1927895178dSrsc // and return the in-memory copy. 19307090dd7Srsc static struct inode* 19411a9947fSrtm iget(uint dev, uint inum) 19511a9947fSrtm { 196bcca6c6bSrsc struct inode *ip, *empty; 19711a9947fSrtm 198bcca6c6bSrsc acquire(&icache.lock); 19911a9947fSrtm 200bcca6c6bSrsc // Try for cached inode. 201bcca6c6bSrsc empty = 0; 202bcca6c6bSrsc for(ip = &icache.inode[0]; ip < &icache.inode[NINODE]; ip++){ 2030d6bbd31Srsc if(ip->ref > 0 && ip->dev == dev && ip->inum == inum){ 2040d6bbd31Srsc ip->ref++; 205bcca6c6bSrsc release(&icache.lock); 20607090dd7Srsc return ip; 20711a9947fSrtm } 208bcca6c6bSrsc if(empty == 0 && ip->ref == 0) // Remember empty slot. 209bcca6c6bSrsc empty = ip; 21011a9947fSrtm } 21111a9947fSrtm 212bcca6c6bSrsc // Allocate fresh inode. 213bcca6c6bSrsc if(empty == 0) 21432eea766Srsc panic("iget: no inodes"); 21511a9947fSrtm 216bcca6c6bSrsc ip = empty; 217bcca6c6bSrsc ip->dev = dev; 218bcca6c6bSrsc ip->inum = inum; 219bcca6c6bSrsc ip->ref = 1; 220f32f3638Srsc ip->flags = 0; 221bcca6c6bSrsc release(&icache.lock); 22211a9947fSrtm 22307090dd7Srsc return ip; 224f32f3638Srsc } 225f32f3638Srsc 226eaea18cbSrsc // Increment reference count for ip. 227eaea18cbSrsc // Returns ip to enable ip = idup(ip1) idiom. 22807090dd7Srsc struct inode* 22907090dd7Srsc idup(struct inode *ip) 230f32f3638Srsc { 231eaea18cbSrsc acquire(&icache.lock); 232eaea18cbSrsc ip->ref++; 233eaea18cbSrsc release(&icache.lock); 23407090dd7Srsc return ip; 235f32f3638Srsc } 236f32f3638Srsc 237f32f3638Srsc // Lock the given inode. 23807090dd7Srsc void 23907090dd7Srsc ilock(struct inode *ip) 240f32f3638Srsc { 241f32f3638Srsc struct buf *bp; 242f32f3638Srsc struct dinode *dip; 243eaea18cbSrsc 24407090dd7Srsc if(ip == 0 || ip->ref < 1) 24507090dd7Srsc panic("ilock"); 246f32f3638Srsc 247f32f3638Srsc acquire(&icache.lock); 248f32f3638Srsc while(ip->flags & I_BUSY) 249f32f3638Srsc sleep(ip, &icache.lock); 250f32f3638Srsc ip->flags |= I_BUSY; 251f32f3638Srsc release(&icache.lock); 252f32f3638Srsc 253f32f3638Srsc if(!(ip->flags & I_VALID)){ 254f32f3638Srsc bp = bread(ip->dev, IBLOCK(ip->inum)); 2553341e30fSrsc dip = (struct dinode*)bp->data + ip->inum%IPB; 256bcca6c6bSrsc ip->type = dip->type; 257bcca6c6bSrsc ip->major = dip->major; 258bcca6c6bSrsc ip->minor = dip->minor; 259bcca6c6bSrsc ip->nlink = dip->nlink; 260bcca6c6bSrsc ip->size = dip->size; 261bcca6c6bSrsc memmove(ip->addrs, dip->addrs, sizeof(ip->addrs)); 26211a9947fSrtm brelse(bp); 263f32f3638Srsc ip->flags |= I_VALID; 264eaea18cbSrsc if(ip->type == 0) 265eaea18cbSrsc panic("ilock: no type"); 26611a9947fSrtm } 267bcca6c6bSrsc } 268bcca6c6bSrsc 269bcca6c6bSrsc // Unlock the given inode. 27007090dd7Srsc void 271bcca6c6bSrsc iunlock(struct inode *ip) 272bcca6c6bSrsc { 27307090dd7Srsc if(ip == 0 || !(ip->flags & I_BUSY) || ip->ref < 1) 274bcca6c6bSrsc panic("iunlock"); 275bcca6c6bSrsc 276bcca6c6bSrsc acquire(&icache.lock); 277ce72cadbSrsc ip->flags &= ~I_BUSY; 278bcca6c6bSrsc wakeup(ip); 279bcca6c6bSrsc release(&icache.lock); 280bcca6c6bSrsc } 281bcca6c6bSrsc 282f32f3638Srsc // Caller holds reference to unlocked ip. Drop reference. 283bcca6c6bSrsc void 28407090dd7Srsc iput(struct inode *ip) 285bcca6c6bSrsc { 286f32f3638Srsc acquire(&icache.lock); 287f32f3638Srsc if(ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0){ 288f32f3638Srsc // inode is no longer used: truncate and free inode. 289f32f3638Srsc if(ip->flags & I_BUSY) 290eaea18cbSrsc panic("iput busy"); 291f32f3638Srsc ip->flags |= I_BUSY; 292f32f3638Srsc release(&icache.lock); 293f32f3638Srsc itrunc(ip); 294f32f3638Srsc ip->type = 0; 295f32f3638Srsc iupdate(ip); 296f32f3638Srsc acquire(&icache.lock); 297ce72cadbSrsc ip->flags = 0; 2988970df0cSrsc wakeup(ip); 299f32f3638Srsc } 300f32f3638Srsc ip->ref--; 301f32f3638Srsc release(&icache.lock); 302bcca6c6bSrsc } 303bcca6c6bSrsc 3047895178dSrsc // Common idiom: unlock, then put. 30507090dd7Srsc void 30607090dd7Srsc iunlockput(struct inode *ip) 30707090dd7Srsc { 30807090dd7Srsc iunlock(ip); 30907090dd7Srsc iput(ip); 31007090dd7Srsc } 31107090dd7Srsc 3128d2e9a48Srsc //PAGEBREAK! 313bcca6c6bSrsc // Inode contents 314bcca6c6bSrsc // 315bcca6c6bSrsc // The contents (data) associated with each inode is stored 316bcca6c6bSrsc // in a sequence of blocks on the disk. The first NDIRECT blocks 3177895178dSrsc // are listed in ip->addrs[]. The next NINDIRECT blocks are 318bcca6c6bSrsc // listed in the block ip->addrs[INDIRECT]. 3199d3fb671Srtm 320bb207a1dSrsc // Return the disk block address of the nth block in inode ip. 32113ae8808Srsc // If there is no such block, bmap allocates one. 322eaea18cbSrsc static uint 32313ae8808Srsc bmap(struct inode *ip, uint bn) 32422bac2cbSkaashoek { 325bcca6c6bSrsc uint addr, *a; 326bcca6c6bSrsc struct buf *bp; 32722bac2cbSkaashoek 328ea2909b6Skaashoek if(bn < NDIRECT){ 32913ae8808Srsc if((addr = ip->addrs[bn]) == 0) 330bcca6c6bSrsc ip->addrs[bn] = addr = balloc(ip->dev); 331bcca6c6bSrsc return addr; 332bcca6c6bSrsc } 333bcca6c6bSrsc bn -= NDIRECT; 334bcca6c6bSrsc 335bcca6c6bSrsc if(bn < NINDIRECT){ 336bcca6c6bSrsc // Load indirect block, allocating if necessary. 33713ae8808Srsc if((addr = ip->addrs[NDIRECT]) == 0) 338ba6cd8a6Srsc ip->addrs[NDIRECT] = addr = balloc(ip->dev); 339bcca6c6bSrsc bp = bread(ip->dev, addr); 340bcca6c6bSrsc a = (uint*)bp->data; 341bcca6c6bSrsc if((addr = a[bn]) == 0){ 342bcca6c6bSrsc a[bn] = addr = balloc(ip->dev); 343eaea18cbSrsc bwrite(bp); 344bcca6c6bSrsc } 345bcca6c6bSrsc brelse(bp); 346bcca6c6bSrsc return addr; 34722bac2cbSkaashoek } 34822bac2cbSkaashoek 349bcca6c6bSrsc panic("bmap: out of range"); 350bcca6c6bSrsc } 351bcca6c6bSrsc 352bcca6c6bSrsc // Truncate inode (discard contents). 3538eb20827Srtm // Only called after the last dirent referring 3548eb20827Srtm // to this inode has been erased on disk. 355fbf91039Srsc static void 3562aa4c3bcSrtm itrunc(struct inode *ip) 35722bac2cbSkaashoek { 358ea2909b6Skaashoek int i, j; 359bcca6c6bSrsc struct buf *bp; 3607d4aef6cSrsc uint *a; 36122bac2cbSkaashoek 362bcca6c6bSrsc for(i = 0; i < NDIRECT; i++){ 363bcca6c6bSrsc if(ip->addrs[i]){ 36422bac2cbSkaashoek bfree(ip->dev, ip->addrs[i]); 36522bac2cbSkaashoek ip->addrs[i] = 0; 36622bac2cbSkaashoek } 36722bac2cbSkaashoek } 368bcca6c6bSrsc 369ba6cd8a6Srsc if(ip->addrs[NDIRECT]){ 370ba6cd8a6Srsc bp = bread(ip->dev, ip->addrs[NDIRECT]); 371bcca6c6bSrsc a = (uint*)bp->data; 372bcca6c6bSrsc for(j = 0; j < NINDIRECT; j++){ 373bcca6c6bSrsc if(a[j]) 374bcca6c6bSrsc bfree(ip->dev, a[j]); 375bcca6c6bSrsc } 376bcca6c6bSrsc brelse(bp); 377ba6cd8a6Srsc bfree(ip->dev, ip->addrs[NDIRECT]); 378ba6cd8a6Srsc ip->addrs[NDIRECT] = 0; 379bcca6c6bSrsc } 380bcca6c6bSrsc 38122bac2cbSkaashoek ip->size = 0; 38222bac2cbSkaashoek iupdate(ip); 38322bac2cbSkaashoek } 38422bac2cbSkaashoek 385bb207a1dSrsc // Copy stat information from inode. 386e958c538Skaashoek void 3871f544842Skaashoek stati(struct inode *ip, struct stat *st) 3881f544842Skaashoek { 3891dca3afbSrsc st->dev = ip->dev; 3901dca3afbSrsc st->ino = ip->inum; 3911dca3afbSrsc st->type = ip->type; 3921dca3afbSrsc st->nlink = ip->nlink; 3931dca3afbSrsc st->size = ip->size; 3941f544842Skaashoek } 3951f544842Skaashoek 396eaea18cbSrsc //PAGEBREAK! 397bb207a1dSrsc // Read data from inode. 398c59361f1Srtm int 39917a85657Srtm readi(struct inode *ip, char *dst, uint off, uint n) 400c59361f1Srtm { 401bcca6c6bSrsc uint tot, m; 402c59361f1Srtm struct buf *bp; 403c59361f1Srtm 404939f9edeSkaashoek if(ip->type == T_DEV){ 4051dca3afbSrsc if(ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].read) 406939f9edeSkaashoek return -1; 407d844f0f9Srsc return devsw[ip->major].read(ip, dst, n); 408939f9edeSkaashoek } 409939f9edeSkaashoek 4107895178dSrsc if(off > ip->size || off + n < off) 411bcca6c6bSrsc return -1; 412bcca6c6bSrsc if(off + n > ip->size) 413bcca6c6bSrsc n = ip->size - off; 414bcca6c6bSrsc 415bcca6c6bSrsc for(tot=0; tot<n; tot+=m, off+=m, dst+=m){ 41613ae8808Srsc bp = bread(ip->dev, bmap(ip, off/BSIZE)); 417bcca6c6bSrsc m = min(n - tot, BSIZE - off%BSIZE); 418bcca6c6bSrsc memmove(dst, bp->data + off%BSIZE, m); 419c59361f1Srtm brelse(bp); 420c59361f1Srtm } 421bcca6c6bSrsc return n; 422ea2909b6Skaashoek } 423ea2909b6Skaashoek 424eaea18cbSrsc // PAGEBREAK! 425bb207a1dSrsc // Write data to inode. 426ea2909b6Skaashoek int 427bcca6c6bSrsc writei(struct inode *ip, char *src, uint off, uint n) 4286fa5ffb5Skaashoek { 429bcca6c6bSrsc uint tot, m; 4307d4aef6cSrsc struct buf *bp; 4317d4aef6cSrsc 4326fa5ffb5Skaashoek if(ip->type == T_DEV){ 4331dca3afbSrsc if(ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].write) 434939f9edeSkaashoek return -1; 435d844f0f9Srsc return devsw[ip->major].write(ip, src, n); 4367d4aef6cSrsc } 4377d4aef6cSrsc 43813ae8808Srsc if(off > ip->size || off + n < off) 439bcca6c6bSrsc return -1; 440bcca6c6bSrsc if(off + n > MAXFILE*BSIZE) 441bcca6c6bSrsc n = MAXFILE*BSIZE - off; 442bcca6c6bSrsc 443bcca6c6bSrsc for(tot=0; tot<n; tot+=m, off+=m, src+=m){ 44413ae8808Srsc bp = bread(ip->dev, bmap(ip, off/BSIZE)); 445bcca6c6bSrsc m = min(n - tot, BSIZE - off%BSIZE); 446bcca6c6bSrsc memmove(bp->data + off%BSIZE, src, m); 447eaea18cbSrsc bwrite(bp); 44828d9ef04Skaashoek brelse(bp); 44928d9ef04Skaashoek } 450bcca6c6bSrsc 451bcca6c6bSrsc if(n > 0 && off > ip->size){ 45248b82470Srsc ip->size = off; 45328d9ef04Skaashoek iupdate(ip); 45428d9ef04Skaashoek } 455bcca6c6bSrsc return n; 4566fa5ffb5Skaashoek } 4576fa5ffb5Skaashoek 458eaea18cbSrsc //PAGEBREAK! 459bcca6c6bSrsc // Directories 460bcca6c6bSrsc 461eaea18cbSrsc int 462fbf91039Srsc namecmp(const char *s, const char *t) 463fbf91039Srsc { 464766ba5ccSrsc return strncmp(s, t, DIRSIZ); 465fbf91039Srsc } 466fbf91039Srsc 467bcca6c6bSrsc // Look for a directory entry in a directory. 468eaea18cbSrsc // If found, set *poff to byte offset of entry. 46920365348Srtm // Caller must have already locked dp. 47007090dd7Srsc struct inode* 471fbf91039Srsc dirlookup(struct inode *dp, char *name, uint *poff) 472bcca6c6bSrsc { 473f32f3638Srsc uint off, inum; 474bcca6c6bSrsc struct buf *bp; 475bcca6c6bSrsc struct dirent *de; 476bcca6c6bSrsc 477bcca6c6bSrsc if(dp->type != T_DIR) 47820365348Srtm panic("dirlookup not DIR"); 479bcca6c6bSrsc 480bcca6c6bSrsc for(off = 0; off < dp->size; off += BSIZE){ 48113ae8808Srsc bp = bread(dp->dev, bmap(dp, off / BSIZE)); 482bcca6c6bSrsc for(de = (struct dirent*)bp->data; 483bcca6c6bSrsc de < (struct dirent*)(bp->data + BSIZE); 484bcca6c6bSrsc de++){ 485bcca6c6bSrsc if(de->inum == 0) 486bcca6c6bSrsc continue; 487fbf91039Srsc if(namecmp(name, de->name) == 0){ 488bcca6c6bSrsc // entry matches path element 489e2a620daSrsc if(poff) 490bcca6c6bSrsc *poff = off + (uchar*)de - bp->data; 491f32f3638Srsc inum = de->inum; 492bcca6c6bSrsc brelse(bp); 493f32f3638Srsc return iget(dp->dev, inum); 494f32f3638Srsc } 495f32f3638Srsc } 496f32f3638Srsc brelse(bp); 497f32f3638Srsc } 498bcca6c6bSrsc return 0; 499bcca6c6bSrsc } 500bcca6c6bSrsc 50113ae8808Srsc // Write a new directory entry (name, inum) into the directory dp. 502eaea18cbSrsc int 50313ae8808Srsc dirlink(struct inode *dp, char *name, uint inum) 504bcca6c6bSrsc { 505e2a620daSrsc int off; 506bcca6c6bSrsc struct dirent de; 50707090dd7Srsc struct inode *ip; 508f32f3638Srsc 509eaea18cbSrsc // Check that name is not present. 51007090dd7Srsc if((ip = dirlookup(dp, name, 0)) != 0){ 51107090dd7Srsc iput(ip); 512f32f3638Srsc return -1; 513f32f3638Srsc } 514bcca6c6bSrsc 515bcca6c6bSrsc // Look for an empty dirent. 516bcca6c6bSrsc for(off = 0; off < dp->size; off += sizeof(de)){ 517bcca6c6bSrsc if(readi(dp, (char*)&de, off, sizeof(de)) != sizeof(de)) 5187895178dSrsc panic("dirlink read"); 519bcca6c6bSrsc if(de.inum == 0) 520bcca6c6bSrsc break; 521bcca6c6bSrsc } 522bcca6c6bSrsc 523766ba5ccSrsc strncpy(de.name, name, DIRSIZ); 52413ae8808Srsc de.inum = inum; 525bcca6c6bSrsc if(writei(dp, (char*)&de, off, sizeof(de)) != sizeof(de)) 5267895178dSrsc panic("dirlink"); 527f32f3638Srsc 528f32f3638Srsc return 0; 529bcca6c6bSrsc } 530bcca6c6bSrsc 5318d2e9a48Srsc //PAGEBREAK! 532bcca6c6bSrsc // Paths 533bcca6c6bSrsc 534eaea18cbSrsc // Copy the next path element from path into name. 535eaea18cbSrsc // Return a pointer to the element following the copied one. 536eaea18cbSrsc // The returned path has no leading slashes, 537eaea18cbSrsc // so the caller can check *path=='\0' to see if the name is the last one. 538eaea18cbSrsc // If no name to remove, return 0. 539ab5c2dbbSrsc // 540ab5c2dbbSrsc // Examples: 541eaea18cbSrsc // skipelem("a/bb/c", name) = "bb/c", setting name = "a" 5427895178dSrsc // skipelem("///a//bb", name) = "bb", setting name = "a" 54313ae8808Srsc // skipelem("a", name) = "", setting name = "a" 544eaea18cbSrsc // skipelem("", name) = skipelem("////", name) = 0 545ab5c2dbbSrsc // 546ab5c2dbbSrsc static char* 547fbf91039Srsc skipelem(char *path, char *name) 548ab5c2dbbSrsc { 549fbf91039Srsc char *s; 550fbf91039Srsc int len; 551fbf91039Srsc 552ab5c2dbbSrsc while(*path == '/') 553ab5c2dbbSrsc path++; 554ab5c2dbbSrsc if(*path == 0) 555ab5c2dbbSrsc return 0; 556fbf91039Srsc s = path; 557ab5c2dbbSrsc while(*path != '/' && *path != 0) 558ab5c2dbbSrsc path++; 559fbf91039Srsc len = path - s; 560fbf91039Srsc if(len >= DIRSIZ) 561fbf91039Srsc memmove(name, s, DIRSIZ); 562fbf91039Srsc else { 563fbf91039Srsc memmove(name, s, len); 564fbf91039Srsc name[len] = 0; 565fbf91039Srsc } 566ab5c2dbbSrsc while(*path == '/') 567ab5c2dbbSrsc path++; 568ab5c2dbbSrsc return path; 569ab5c2dbbSrsc } 570ab5c2dbbSrsc 571eaea18cbSrsc // Look up and return the inode for a path name. 572bf2932a6Srsc // If parent != 0, return the inode for the parent and copy the final 573bf2932a6Srsc // path element into name, which must have room for DIRSIZ bytes. 57407090dd7Srsc static struct inode* 575*f9a06440SRuss Cox namex(char *path, int nameiparent, char *name) 5769d3fb671Srtm { 57707090dd7Srsc struct inode *ip, *next; 5789d3fb671Srtm 579ab5c2dbbSrsc if(*path == '/') 5802ce40d70Srtm ip = iget(ROOTDEV, ROOTINO); 581f32f3638Srsc else 58207090dd7Srsc ip = idup(cp->cwd); 5839d3fb671Srtm 584fbf91039Srsc while((path = skipelem(path, name)) != 0){ 58507090dd7Srsc ilock(ip); 58607090dd7Srsc if(ip->type != T_DIR){ 58707090dd7Srsc iunlockput(ip); 588eaea18cbSrsc return 0; 589eaea18cbSrsc } 590*f9a06440SRuss Cox if(nameiparent && *path == '\0'){ 591e2a620daSrsc // Stop one level early. 59207090dd7Srsc iunlock(ip); 59307090dd7Srsc return ip; 594ab5c2dbbSrsc } 5957895178dSrsc if((next = dirlookup(ip, name, 0)) == 0){ 59607090dd7Srsc iunlockput(ip); 597eaea18cbSrsc return 0; 598eaea18cbSrsc } 59907090dd7Srsc iunlockput(ip); 60007090dd7Srsc ip = next; 601ab5c2dbbSrsc } 602*f9a06440SRuss Cox if(nameiparent){ 60307090dd7Srsc iput(ip); 6045051da6dSrtm return 0; 60520365348Srtm } 60607090dd7Srsc return ip; 6070633b971Skaashoek } 6089d3fb671Srtm 6097895178dSrsc struct inode* 6107895178dSrsc namei(char *path) 6117895178dSrsc { 6127895178dSrsc char name[DIRSIZ]; 61313ae8808Srsc return namex(path, 0, name); 6147895178dSrsc } 615bf2932a6Srsc 6167895178dSrsc struct inode* 6177895178dSrsc nameiparent(char *path, char *name) 6187895178dSrsc { 61913ae8808Srsc return namex(path, 1, name); 6207895178dSrsc } 621