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 82e590463SRobert Morris // Simple logging. Each system call that might write the file system 92e590463SRobert Morris // should be surrounded with begin_trans() and commit_trans() calls. 102e590463SRobert Morris // 112e590463SRobert Morris // The log holds at most one transaction at a time. Commit forces 122e590463SRobert Morris // the log (with commit record) to disk, then installs the affected 132e590463SRobert Morris // blocks to disk, then erases the log. begin_trans() ensures that 142e590463SRobert Morris // only one system call can be in a transaction; others must wait. 152e590463SRobert Morris // 162e590463SRobert Morris // Allowing only one transaction at a time means that the file 172e590463SRobert Morris // system code doesn't have to worry about the possibility of 182e590463SRobert Morris // one transaction reading a block that another one has modified, 192e590463SRobert Morris // for example an i-node block. 202e590463SRobert Morris // 212e590463SRobert Morris // Read-only system calls don't need to use transactions, though 22a14c96f8SAustin Clements // this means that they may observe uncommitted data. I-node and 23a14c96f8SAustin Clements // buffer locks prevent read-only calls from seeing inconsistent data. 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; 451ddfbbb1SFrans Kaashoek int intrans; 4613a96baeSFrans Kaashoek int dev; 4713a96baeSFrans Kaashoek struct logheader lh; 48ee1b3306SAustin Clements }; 49ee1b3306SAustin Clements struct log log; 5013a96baeSFrans Kaashoek 5113a96baeSFrans Kaashoek static void recover_from_log(void); 5213a96baeSFrans Kaashoek 5313a96baeSFrans Kaashoek void 5413a96baeSFrans Kaashoek initlog(void) 5513a96baeSFrans Kaashoek { 5613a96baeSFrans Kaashoek if (sizeof(struct logheader) >= BSIZE) 5713a96baeSFrans Kaashoek panic("initlog: too big logheader"); 5813a96baeSFrans Kaashoek 5913a96baeSFrans Kaashoek struct superblock sb; 6013a96baeSFrans Kaashoek initlock(&log.lock, "log"); 6113a96baeSFrans Kaashoek readsb(ROOTDEV, &sb); 6213a96baeSFrans Kaashoek log.start = sb.size - sb.nlog; 6313a96baeSFrans Kaashoek log.size = sb.nlog; 6413a96baeSFrans Kaashoek log.dev = ROOTDEV; 6513a96baeSFrans Kaashoek recover_from_log(); 6613a96baeSFrans Kaashoek } 6713a96baeSFrans Kaashoek 6813a96baeSFrans Kaashoek // Copy committed blocks from log to their home location 6913a96baeSFrans Kaashoek static void 7013a96baeSFrans Kaashoek install_trans(void) 7113a96baeSFrans Kaashoek { 7213a96baeSFrans Kaashoek int tail; 7313a96baeSFrans Kaashoek 742e590463SRobert Morris for (tail = 0; tail < log.lh.n; tail++) { 75e25b74caSFrans Kaashoek struct buf *lbuf = bread(log.dev, log.start+tail+1); // read log block 76e25b74caSFrans Kaashoek struct buf *dbuf = bread(log.dev, log.lh.sector[tail]); // read dst 77e25b74caSFrans Kaashoek memmove(dbuf->data, lbuf->data, BSIZE); // copy block to dst 78e25b74caSFrans Kaashoek bwrite(dbuf); // flush dst to disk 7913a96baeSFrans Kaashoek brelse(lbuf); 8013a96baeSFrans Kaashoek brelse(dbuf); 8113a96baeSFrans Kaashoek } 8213a96baeSFrans Kaashoek } 8313a96baeSFrans Kaashoek 8413a96baeSFrans Kaashoek // Read the log header from disk into the in-memory log header 8513a96baeSFrans Kaashoek static void 8613a96baeSFrans Kaashoek read_head(void) 8713a96baeSFrans Kaashoek { 8813a96baeSFrans Kaashoek struct buf *buf = bread(log.dev, log.start); 8913a96baeSFrans Kaashoek struct logheader *lh = (struct logheader *) (buf->data); 9013a96baeSFrans Kaashoek int i; 912e590463SRobert Morris log.lh.n = lh->n; 922e590463SRobert Morris for (i = 0; i < log.lh.n; i++) { 9313a96baeSFrans Kaashoek log.lh.sector[i] = lh->sector[i]; 9413a96baeSFrans Kaashoek } 9513a96baeSFrans Kaashoek brelse(buf); 9613a96baeSFrans Kaashoek } 9713a96baeSFrans Kaashoek 98e25b74caSFrans Kaashoek // Write in-memory log header to disk, committing log entries till head 9913a96baeSFrans Kaashoek static void 10013a96baeSFrans Kaashoek write_head(void) 10113a96baeSFrans Kaashoek { 10213a96baeSFrans Kaashoek struct buf *buf = bread(log.dev, log.start); 10313a96baeSFrans Kaashoek struct logheader *hb = (struct logheader *) (buf->data); 10413a96baeSFrans Kaashoek int i; 1052e590463SRobert Morris hb->n = log.lh.n; 1062e590463SRobert Morris for (i = 0; i < log.lh.n; i++) { 10713a96baeSFrans Kaashoek hb->sector[i] = log.lh.sector[i]; 10813a96baeSFrans Kaashoek } 10913a96baeSFrans Kaashoek bwrite(buf); 11013a96baeSFrans Kaashoek brelse(buf); 11113a96baeSFrans Kaashoek } 11213a96baeSFrans Kaashoek 11313a96baeSFrans Kaashoek static void 11413a96baeSFrans Kaashoek recover_from_log(void) 11513a96baeSFrans Kaashoek { 11613a96baeSFrans Kaashoek read_head(); 1175053dd6aSRobert Morris install_trans(); // if committed, copy from log to disk 1182e590463SRobert Morris log.lh.n = 0; 1195053dd6aSRobert Morris write_head(); // clear the log 12013a96baeSFrans Kaashoek } 12113a96baeSFrans Kaashoek 12213a96baeSFrans Kaashoek void 12313a96baeSFrans Kaashoek begin_trans(void) 12413a96baeSFrans Kaashoek { 12513a96baeSFrans Kaashoek acquire(&log.lock); 1261ddfbbb1SFrans Kaashoek while (log.intrans) { 1271ddfbbb1SFrans Kaashoek sleep(&log, &log.lock); 1281ddfbbb1SFrans Kaashoek } 1291ddfbbb1SFrans Kaashoek log.intrans = 1; 13013a96baeSFrans Kaashoek release(&log.lock); 13113a96baeSFrans Kaashoek } 13213a96baeSFrans Kaashoek 13313a96baeSFrans Kaashoek void 13413a96baeSFrans Kaashoek commit_trans(void) 13513a96baeSFrans Kaashoek { 136843eecfcSAustin Clements if (log.lh.n > 0) { 137e25b74caSFrans Kaashoek write_head(); // Causes all blocks till log.head to be commited 13813a96baeSFrans Kaashoek install_trans(); // Install all the transactions till head 1392e590463SRobert Morris log.lh.n = 0; 14013a96baeSFrans Kaashoek write_head(); // Reclaim log 141843eecfcSAustin Clements } 1421ddfbbb1SFrans Kaashoek 14313a96baeSFrans Kaashoek acquire(&log.lock); 1441ddfbbb1SFrans Kaashoek log.intrans = 0; 1451ddfbbb1SFrans Kaashoek wakeup(&log); 14613a96baeSFrans Kaashoek release(&log.lock); 14713a96baeSFrans Kaashoek } 14813a96baeSFrans Kaashoek 1492e590463SRobert Morris // Caller has modified b->data and is done with the buffer. 1502e590463SRobert Morris // Append the block to the log and record the block number, 1512e590463SRobert Morris // but don't write the log header (which would commit the write). 1522e590463SRobert Morris // log_write() replaces bwrite(); a typical use is: 1532e590463SRobert Morris // bp = bread(...) 1542e590463SRobert Morris // modify bp->data[] 1552e590463SRobert Morris // log_write(bp) 1562e590463SRobert Morris // brelse(bp) 15713a96baeSFrans Kaashoek void 15813a96baeSFrans Kaashoek log_write(struct buf *b) 15913a96baeSFrans Kaashoek { 16013a96baeSFrans Kaashoek int i; 16113a96baeSFrans Kaashoek 1622e590463SRobert Morris if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1) 16313a96baeSFrans Kaashoek panic("too big a transaction"); 1641ddfbbb1SFrans Kaashoek if (!log.intrans) 16513a96baeSFrans Kaashoek panic("write outside of trans"); 16613a96baeSFrans Kaashoek 1672e590463SRobert Morris for (i = 0; i < log.lh.n; i++) { 16813a96baeSFrans Kaashoek if (log.lh.sector[i] == b->sector) // log absorbtion? 16913a96baeSFrans Kaashoek break; 17013a96baeSFrans Kaashoek } 17113a96baeSFrans Kaashoek log.lh.sector[i] = b->sector; 17213a96baeSFrans Kaashoek struct buf *lbuf = bread(b->dev, log.start+i+1); 17313a96baeSFrans Kaashoek memmove(lbuf->data, b->data, BSIZE); 17413a96baeSFrans Kaashoek bwrite(lbuf); 17513a96baeSFrans Kaashoek brelse(lbuf); 1762e590463SRobert Morris if (i == log.lh.n) 1772e590463SRobert Morris log.lh.n++; 17813a96baeSFrans Kaashoek } 179*9bb1e53dSAustin Clements 180*9bb1e53dSAustin Clements //PAGEBREAK! 181*9bb1e53dSAustin Clements // Blank page. 182*9bb1e53dSAustin Clements 183