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authorRobert Morris <[email protected]>2014-08-28 16:06:12 -0400
committerRobert Morris <[email protected]>2014-08-28 16:06:12 -0400
commit2b2c1971fc2c3cc6fa1f2f3e7b507a3a35a0cbb8 (patch)
treec9ec9a82671f6af27d72d545aba3746302b4b157 /log.c
parent11183588dc69085b834e013564fc48526e23ef70 (diff)
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write log blocks from cache only at end of transaction
Diffstat (limited to 'log.c')
-rw-r--r--log.c28
1 files changed, 21 insertions, 7 deletions
diff --git a/log.c b/log.c
index 6900b8d..0abe1fe 100644
--- a/log.c
+++ b/log.c
@@ -170,10 +170,27 @@ end_op(void)
}
}
+// 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;
@@ -182,8 +199,9 @@ commit()
}
// 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[]
@@ -197,17 +215,13 @@ log_write(struct buf *b)
if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1)
panic("too big a transaction");
if (log.outstanding < 1)
- panic("write outside of trans");
+ panic("log_write outside of trans");
for (i = 0; i < log.lh.n; i++) {
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; // prevent eviction