113a96baeSFrans Kaashoek #include "types.h" 213a96baeSFrans Kaashoek #include "defs.h" 313a96baeSFrans Kaashoek #include "param.h" 413a96baeSFrans Kaashoek #include "spinlock.h" 513a96baeSFrans Kaashoek #include "fs.h" 613a96baeSFrans Kaashoek #include "buf.h" 713a96baeSFrans Kaashoek 8*71453f72SRobert Morris // Simple logging that allows concurrent FS system calls. 92e590463SRobert Morris // 10*71453f72SRobert Morris // A log transaction contains the updates of *multiple* FS system 11*71453f72SRobert Morris // calls. The logging systems only commits when there are 12*71453f72SRobert Morris // no FS system calls active. Thus there is never 13*71453f72SRobert Morris // any reasoning required about whether a commit might 14*71453f72SRobert Morris // write an uncommitted system call's updates to disk. 152e590463SRobert Morris // 16*71453f72SRobert Morris // A system call should call begin_op()/end_op() to mark 17*71453f72SRobert Morris // its start and end. Usually begin_op() just increments 18*71453f72SRobert Morris // the count of in-progress FS system calls and returns. 19*71453f72SRobert Morris // But if it thinks the log is close to running out, it 20*71453f72SRobert Morris // blocks this system call, and causes the system to wait 21*71453f72SRobert Morris // until end_op() indicates there are no executing FS 22*71453f72SRobert Morris // system calls, at which point the last end_op() commits 23*71453f72SRobert Morris // all the system calls' writes. 242e590463SRobert Morris // 252e590463SRobert Morris // The log is a physical re-do log containing disk blocks. 262e590463SRobert Morris // The on-disk log format: 272e590463SRobert Morris // header block, containing sector #s for block A, B, C, ... 282e590463SRobert Morris // block A 292e590463SRobert Morris // block B 302e590463SRobert Morris // block C 312e590463SRobert Morris // ... 322e590463SRobert Morris // Log appends are synchronous. 3313a96baeSFrans Kaashoek 342e590463SRobert Morris // Contents of the header block, used for both the on-disk header block 352e590463SRobert Morris // and to keep track in memory of logged sector #s before commit. 3613a96baeSFrans Kaashoek struct logheader { 372e590463SRobert Morris int n; 3813a96baeSFrans Kaashoek int sector[LOGSIZE]; 3913a96baeSFrans Kaashoek }; 4013a96baeSFrans Kaashoek 41ee1b3306SAustin Clements struct log { 4213a96baeSFrans Kaashoek struct spinlock lock; 4313a96baeSFrans Kaashoek int start; 4413a96baeSFrans Kaashoek int size; 45*71453f72SRobert Morris int outstanding; // how many FS sys calls are executing. 46*71453f72SRobert Morris int committing; // in commit(), please wait. 4713a96baeSFrans Kaashoek int dev; 4813a96baeSFrans Kaashoek struct logheader lh; 49ee1b3306SAustin Clements }; 50ee1b3306SAustin Clements struct log log; 5113a96baeSFrans Kaashoek 5213a96baeSFrans Kaashoek static void recover_from_log(void); 53*71453f72SRobert Morris static void commit(); 5413a96baeSFrans Kaashoek 5513a96baeSFrans Kaashoek void 5613a96baeSFrans Kaashoek initlog(void) 5713a96baeSFrans Kaashoek { 5813a96baeSFrans Kaashoek if (sizeof(struct logheader) >= BSIZE) 5913a96baeSFrans Kaashoek panic("initlog: too big logheader"); 6013a96baeSFrans Kaashoek 6113a96baeSFrans Kaashoek struct superblock sb; 6213a96baeSFrans Kaashoek initlock(&log.lock, "log"); 6313a96baeSFrans Kaashoek readsb(ROOTDEV, &sb); 6413a96baeSFrans Kaashoek log.start = sb.size - sb.nlog; 6513a96baeSFrans Kaashoek log.size = sb.nlog; 6613a96baeSFrans Kaashoek log.dev = ROOTDEV; 6713a96baeSFrans Kaashoek recover_from_log(); 6813a96baeSFrans Kaashoek } 6913a96baeSFrans Kaashoek 7013a96baeSFrans Kaashoek // Copy committed blocks from log to their home location 7113a96baeSFrans Kaashoek static void 7213a96baeSFrans Kaashoek install_trans(void) 7313a96baeSFrans Kaashoek { 7413a96baeSFrans Kaashoek int tail; 7513a96baeSFrans Kaashoek 762e590463SRobert Morris for (tail = 0; tail < log.lh.n; tail++) { 77e25b74caSFrans Kaashoek struct buf *lbuf = bread(log.dev, log.start+tail+1); // read log block 78e25b74caSFrans Kaashoek struct buf *dbuf = bread(log.dev, log.lh.sector[tail]); // read dst 79e25b74caSFrans Kaashoek memmove(dbuf->data, lbuf->data, BSIZE); // copy block to dst 80a5fbfe41SRobert Morris bwrite(dbuf); // write dst to disk 8113a96baeSFrans Kaashoek brelse(lbuf); 8213a96baeSFrans Kaashoek brelse(dbuf); 8313a96baeSFrans Kaashoek } 8413a96baeSFrans Kaashoek } 8513a96baeSFrans Kaashoek 8613a96baeSFrans Kaashoek // Read the log header from disk into the in-memory log header 8713a96baeSFrans Kaashoek static void 8813a96baeSFrans Kaashoek read_head(void) 8913a96baeSFrans Kaashoek { 9013a96baeSFrans Kaashoek struct buf *buf = bread(log.dev, log.start); 9113a96baeSFrans Kaashoek struct logheader *lh = (struct logheader *) (buf->data); 9213a96baeSFrans Kaashoek int i; 932e590463SRobert Morris log.lh.n = lh->n; 942e590463SRobert Morris for (i = 0; i < log.lh.n; i++) { 9513a96baeSFrans Kaashoek log.lh.sector[i] = lh->sector[i]; 9613a96baeSFrans Kaashoek } 9713a96baeSFrans Kaashoek brelse(buf); 9813a96baeSFrans Kaashoek } 9913a96baeSFrans Kaashoek 100a5fbfe41SRobert Morris // Write in-memory log header to disk. 101a5fbfe41SRobert Morris // This is the true point at which the 102a5fbfe41SRobert Morris // current transaction commits. 10313a96baeSFrans Kaashoek static void 10413a96baeSFrans Kaashoek write_head(void) 10513a96baeSFrans Kaashoek { 10613a96baeSFrans Kaashoek struct buf *buf = bread(log.dev, log.start); 10713a96baeSFrans Kaashoek struct logheader *hb = (struct logheader *) (buf->data); 10813a96baeSFrans Kaashoek int i; 1092e590463SRobert Morris hb->n = log.lh.n; 1102e590463SRobert Morris for (i = 0; i < log.lh.n; i++) { 11113a96baeSFrans Kaashoek hb->sector[i] = log.lh.sector[i]; 11213a96baeSFrans Kaashoek } 11313a96baeSFrans Kaashoek bwrite(buf); 11413a96baeSFrans Kaashoek brelse(buf); 11513a96baeSFrans Kaashoek } 11613a96baeSFrans Kaashoek 11713a96baeSFrans Kaashoek static void 11813a96baeSFrans Kaashoek recover_from_log(void) 11913a96baeSFrans Kaashoek { 12013a96baeSFrans Kaashoek read_head(); 1215053dd6aSRobert Morris install_trans(); // if committed, copy from log to disk 1222e590463SRobert Morris log.lh.n = 0; 1235053dd6aSRobert Morris write_head(); // clear the log 12413a96baeSFrans Kaashoek } 12513a96baeSFrans Kaashoek 126*71453f72SRobert Morris // an FS system call should call begin_op() when it starts. 12713a96baeSFrans Kaashoek void 128*71453f72SRobert Morris begin_op(void) 12913a96baeSFrans Kaashoek { 13013a96baeSFrans Kaashoek acquire(&log.lock); 131*71453f72SRobert Morris while(1){ 132*71453f72SRobert Morris if(log.committing){ 1331ddfbbb1SFrans Kaashoek sleep(&log, &log.lock); 134*71453f72SRobert Morris } else { 135*71453f72SRobert Morris // XXX wait (for a commit) if log is longish. 136*71453f72SRobert Morris // need to reserve to avoid over-commit of log space. 137*71453f72SRobert Morris log.outstanding += 1; 13813a96baeSFrans Kaashoek release(&log.lock); 139*71453f72SRobert Morris break; 140*71453f72SRobert Morris } 141*71453f72SRobert Morris } 14213a96baeSFrans Kaashoek } 14313a96baeSFrans Kaashoek 144*71453f72SRobert Morris // an FS system call should call end_op() after it finishes. 145*71453f72SRobert Morris // can't write the disk &c while holding locks, thus do_commit. 14613a96baeSFrans Kaashoek void 147*71453f72SRobert Morris end_op(void) 148*71453f72SRobert Morris { 149*71453f72SRobert Morris int do_commit = 0; 150*71453f72SRobert Morris 151*71453f72SRobert Morris acquire(&log.lock); 152*71453f72SRobert Morris log.outstanding -= 1; 153*71453f72SRobert Morris if(log.committing) 154*71453f72SRobert Morris panic("log.committing"); 155*71453f72SRobert Morris if(log.outstanding == 0){ 156*71453f72SRobert Morris do_commit = 1; 157*71453f72SRobert Morris log.committing = 1; 158*71453f72SRobert Morris } 159*71453f72SRobert Morris release(&log.lock); 160*71453f72SRobert Morris 161*71453f72SRobert Morris if(do_commit){ 162*71453f72SRobert Morris commit(); 163*71453f72SRobert Morris acquire(&log.lock); 164*71453f72SRobert Morris log.committing = 0; 165*71453f72SRobert Morris wakeup(&log); 166*71453f72SRobert Morris release(&log.lock); 167*71453f72SRobert Morris } 168*71453f72SRobert Morris } 169*71453f72SRobert Morris 170*71453f72SRobert Morris static void 171*71453f72SRobert Morris commit() 17213a96baeSFrans Kaashoek { 173843eecfcSAustin Clements if (log.lh.n > 0) { 174a5fbfe41SRobert Morris write_head(); // Write header to disk -- the real commit 175a5fbfe41SRobert Morris install_trans(); // Now install writes to home locations 1762e590463SRobert Morris log.lh.n = 0; 177a5fbfe41SRobert Morris write_head(); // Erase the transaction from the log 178843eecfcSAustin Clements } 17913a96baeSFrans Kaashoek } 18013a96baeSFrans Kaashoek 1812e590463SRobert Morris // Caller has modified b->data and is done with the buffer. 1822e590463SRobert Morris // Append the block to the log and record the block number, 1832e590463SRobert Morris // but don't write the log header (which would commit the write). 1842e590463SRobert Morris // log_write() replaces bwrite(); a typical use is: 1852e590463SRobert Morris // bp = bread(...) 1862e590463SRobert Morris // modify bp->data[] 1872e590463SRobert Morris // log_write(bp) 1882e590463SRobert Morris // brelse(bp) 18913a96baeSFrans Kaashoek void 19013a96baeSFrans Kaashoek log_write(struct buf *b) 19113a96baeSFrans Kaashoek { 19213a96baeSFrans Kaashoek int i; 19313a96baeSFrans Kaashoek 1942e590463SRobert Morris if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1) 19513a96baeSFrans Kaashoek panic("too big a transaction"); 196*71453f72SRobert Morris if (log.outstanding < 1) 19713a96baeSFrans Kaashoek panic("write outside of trans"); 19813a96baeSFrans Kaashoek 1992e590463SRobert Morris for (i = 0; i < log.lh.n; i++) { 20013a96baeSFrans Kaashoek if (log.lh.sector[i] == b->sector) // log absorbtion? 20113a96baeSFrans Kaashoek break; 20213a96baeSFrans Kaashoek } 20313a96baeSFrans Kaashoek log.lh.sector[i] = b->sector; 20413a96baeSFrans Kaashoek struct buf *lbuf = bread(b->dev, log.start+i+1); 20513a96baeSFrans Kaashoek memmove(lbuf->data, b->data, BSIZE); 20613a96baeSFrans Kaashoek bwrite(lbuf); 20713a96baeSFrans Kaashoek brelse(lbuf); 2082e590463SRobert Morris if (i == log.lh.n) 2092e590463SRobert Morris log.lh.n++; 21012abb1a5SRobert Morris b->flags |= B_DIRTY; // XXX prevent eviction 21113a96baeSFrans Kaashoek } 2129bb1e53dSAustin Clements 2139bb1e53dSAustin Clements //PAGEBREAK! 2149bb1e53dSAustin Clements // Blank page. 2159bb1e53dSAustin Clements 216