Merge branch 'master' of git+ssh://amsterdam.csail.mit.edu/home/am0/6…

….828/xv6

bio.c

@@ -80,6 +80,8 @@ bget(uint dev, uint sector)
   }
 
   // Not cached; recycle some non-busy and clean buffer.
+  // "clean" because B_DIRTY and !B_BUSY means log.c
+  // hasn't yet committed the changes to the buffer.
   for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
     if((b->flags & B_BUSY) == 0 && (b->flags & B_DIRTY) == 0){
       b->dev = dev;

defs.h

@@ -81,8 +81,8 @@ void            microdelay(int);
 // log.c
 void            initlog(void);
 void            log_write(struct buf*);
-void            begin_trans();
-void            commit_trans();
+void            begin_op();
+void            end_op();
 
 // mp.c
 extern int      ismp;

exec.c

@@ -18,9 +18,9 @@ exec(char *path, char **argv)
   struct proghdr ph;
   pde_t *pgdir, *oldpgdir;
 
-  begin_trans();
+  begin_op();
   if((ip = namei(path)) == 0){
-    commit_trans();
+    end_op();
     return -1;
   }
   ilock(ip);
@@ -50,7 +50,7 @@ exec(char *path, char **argv)
       goto bad;
   }
   iunlockput(ip);
-  commit_trans();
+  end_op();
   ip = 0;
 
   // Allocate two pages at the next page boundary.
@@ -101,7 +101,7 @@ exec(char *path, char **argv)
     freevm(pgdir);
   if(ip){
     iunlockput(ip);
-    commit_trans();
+    end_op();
   }
   return -1;
 }

file.c

@@ -72,9 +72,9 @@ fileclose(struct file *f)
   if(ff.type == FD_PIPE)
     pipeclose(ff.pipe, ff.writable);
   else if(ff.type == FD_INODE){
-    begin_trans();
+    begin_op();
     iput(ff.ip);
-    commit_trans();
+    end_op();
   }
 }
 
@@ -136,12 +136,12 @@ filewrite(struct file *f, char *addr, int n)
       if(n1 > max)
         n1 = max;
 
-      begin_trans();
+      begin_op();
       ilock(f->ip);
       if ((r = writei(f->ip, addr + i, f->off, n1)) > 0)
         f->off += r;
       iunlock(f->ip);
-      commit_trans();
+      end_op();
 
       if(r < 0)
         break;

log.c

@@ -5,18 +5,19 @@
 #include "fs.h"
 #include "buf.h"
 
-// Simple logging. Each file system system call
-// should be surrounded with begin_trans() and commit_trans() calls.
+// Simple logging that allows concurrent FS system calls.
 //
-// The log holds at most one transaction at a time. Commit forces
-// the log (with commit record) to disk, then installs the affected
-// blocks to disk, then erases the log. begin_trans() ensures that
-// only one system call can be in a transaction; others must wait.
-// 
-// Allowing only one transaction at a time means that the file
-// system code doesn't have to worry about the possibility of
-// one transaction reading a block that another one has modified,
-// for example an i-node block.
+// A log transaction contains the updates of multiple FS system
+// calls. The logging system only commits when there are
+// no FS system calls active. Thus there is never
+// any reasoning required about whether a commit might
+// write an uncommitted system call's updates to disk.
+//
+// A system call should call begin_op()/end_op() to mark
+// its start and end. Usually begin_op() just increments
+// the count of in-progress FS system calls and returns.
+// But if it thinks the log is close to running out, it
+// sleeps until the last outstanding end_op() commits.
 //
 // The log is a physical re-do log containing disk blocks.
 // The on-disk log format:
@@ -38,13 +39,15 @@ struct log {
   struct spinlock lock;
   int start;
   int size;
-  int busy; // a transaction is active
+  int outstanding; // how many FS sys calls are executing.
+  int committing;  // in commit(), please wait.
   int dev;
   struct logheader lh;
 };
 struct log log;
 
 static void recover_from_log(void);
+static void commit();
 
 void
 initlog(void)
@@ -117,36 +120,88 @@ recover_from_log(void)
   write_head(); // clear the log
 }
 
+// called at the start of each FS system call.
 void
-begin_trans(void)
+begin_op(void)
 {
   acquire(&log.lock);
-  while (log.busy) {
-    sleep(&log, &log.lock);
+  while(1){
+    if(log.committing){
+      sleep(&log, &log.lock);
+    } else if(log.lh.n + (log.outstanding+1)*MAXOPBLOCKS > LOGSIZE){
+      // this op might exhaust log space; wait for commit.
+      sleep(&log, &log.lock);
+    } else {
+      log.outstanding += 1;
+      release(&log.lock);
+      break;
+    }
   }
-  log.busy = 1;
-  release(&log.lock);
 }
 
+// called at the end of each FS system call.
+// commits if this was the last outstanding operation.
 void
-commit_trans(void)
+end_op(void)
+{
+  int do_commit = 0;
+
+  acquire(&log.lock);
+  log.outstanding -= 1;
+  if(log.committing)
+    panic("log.committing");
+  if(log.outstanding == 0){
+    do_commit = 1;
+    log.committing = 1;
+  } else {
+    // begin_op() may be waiting for log space.
+    wakeup(&log);
+  }
+  release(&log.lock);
+
+  if(do_commit){
+    // call commit w/o holding locks, since not allowed
+    // to sleep with locks.
+    commit();
+    acquire(&log.lock);
+    log.committing = 0;
+    wakeup(&log);
+    release(&log.lock);
+  }
+}
+
+// Copy modified blocks from cache to log.
+static void 
+write_log(void)
+{
+  int tail;
+
+  for (tail = 0; tail < log.lh.n; tail++) {
+    struct buf *to = bread(log.dev, log.start+tail+1); // log block
+    struct buf *from = bread(log.dev, log.lh.sector[tail]); // cache block
+    memmove(to->data, from->data, BSIZE);
+    bwrite(to);  // write the log
+    brelse(from); 
+    brelse(to);
+  }
+}
+
+static void
+commit()
 {
   if (log.lh.n > 0) {
+    write_log();     // Write modified blocks from cache to log
     write_head();    // Write header to disk -- the real commit
     install_trans(); // Now install writes to home locations
     log.lh.n = 0; 
     write_head();    // Erase the transaction from the log
   }
-
-  acquire(&log.lock);
-  log.busy = 0;
-  wakeup(&log);
-  release(&log.lock);
 }
 
 // Caller has modified b->data and is done with the buffer.
-// Append the block to the log and record the block number, 
-// but don't write the log header (which would commit the write).
+// Record the block number and pin in the cache with B_DIRTY.
+// commit()/write_log() will do the disk write.
+//
 // log_write() replaces bwrite(); a typical use is:
 //   bp = bread(...)
 //   modify bp->data[]
@@ -159,21 +214,17 @@ log_write(struct buf *b)
 
   if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1)
     panic("too big a transaction");
-  if (!log.busy)
-    panic("write outside of trans");
+  if (log.outstanding < 1)
+    panic("log_write outside of trans");
 
   for (i = 0; i < log.lh.n; i++) {
-    if (log.lh.sector[i] == b->sector)   // log absorbtion?
+    if (log.lh.sector[i] == b->sector)   // log absorbtion
       break;
   }
   log.lh.sector[i] = b->sector;
-  struct buf *lbuf = bread(b->dev, log.start+i+1);
-  memmove(lbuf->data, b->data, BSIZE);
-  bwrite(lbuf);
-  brelse(lbuf);
   if (i == log.lh.n)
     log.lh.n++;
-  b->flags |= B_DIRTY; // XXX prevent eviction
+  b->flags |= B_DIRTY; // prevent eviction
 }
 
 //PAGEBREAK!

mkfs.c

@@ -13,7 +13,7 @@
 
 #define static_assert(a, b) do { switch (0) case 0: case (a): ; } while (0)
 
-int nblocks = 985;
+int nblocks = (995-LOGSIZE);
 int nlog = LOGSIZE;
 int ninodes = 200;
 int size = 1024;

param.h

@@ -3,10 +3,11 @@
 #define NCPU          8  // maximum number of CPUs
 #define NOFILE       16  // open files per process
 #define NFILE       100  // open files per system
-#define NBUF         10  // size of disk block cache
 #define NINODE       50  // maximum number of active i-nodes
 #define NDEV         10  // maximum major device number
 #define ROOTDEV       1  // device number of file system root disk
 #define MAXARG       32  // max exec arguments
-#define LOGSIZE      10  // max data sectors in on-disk log
+#define MAXOPBLOCKS  10  // max # of blocks any FS op writes
+#define LOGSIZE      (MAXOPBLOCKS*3)  // max data sectors in on-disk log
+#define NBUF         (MAXOPBLOCKS*3)  // size of disk block cache (>= LOGSIZE)
 

proc.c

@@ -186,9 +186,9 @@ exit(void)
     }
   }
 
-  begin_trans();
+  begin_op();
   iput(proc->cwd);
-  commit_trans();
+  end_op();
   proc->cwd = 0;
 
   acquire(&ptable.lock);