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This commit is contained in:
Robert Morris 2014-08-28 06:27:01 -04:00
parent 48aa917403
commit 11183588dc
1 changed files with 10 additions and 24 deletions
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34
log.c
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@ -7,8 +7,8 @@
// Simple logging that allows concurrent FS system calls.
//
// A log transaction contains the updates of *multiple* FS system
// calls. The logging systems only commits when there are
// 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.
@ -17,10 +17,7 @@
// 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
// blocks this system call, and causes the system to wait
// until end_op() indicates there are no executing FS
// system calls, at which point the last end_op() commits
// all the system calls' writes.
// sleeps until the last outstanding end_op() commits.
//
// The log is a physical re-do log containing disk blocks.
// The on-disk log format:
@ -52,10 +49,6 @@ struct log log;
static void recover_from_log(void);
static void commit();
// statistics, delete eventually XXX.
static int maxsize;
static int maxoutstanding;
void
initlog(void)
{
@ -127,7 +120,7 @@ recover_from_log(void)
write_head(); // clear the log
}
// an FS system call should call begin_op() when it starts.
// called at the start of each FS system call.
void
begin_op(void)
{
@ -140,18 +133,14 @@ begin_op(void)
sleep(&log, &log.lock);
} else {
log.outstanding += 1;
if(log.outstanding > maxoutstanding){
maxoutstanding = log.outstanding;
cprintf("%d outstanding\n", log.outstanding);
}
release(&log.lock);
break;
}
}
}
// an FS system call should call end_op() after it finishes.
// can't write the disk &c while holding locks, thus do_commit.
// called at the end of each FS system call.
// commits if this was the last outstanding operation.
void
end_op(void)
{
@ -171,6 +160,8 @@ end_op(void)
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;
@ -209,7 +200,7 @@ log_write(struct buf *b)
panic("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;
@ -219,12 +210,7 @@ log_write(struct buf *b)
brelse(lbuf);
if (i == log.lh.n)
log.lh.n++;
b->flags |= B_DIRTY; // XXX prevent eviction
if(log.lh.n > maxsize){
maxsize = log.lh.n;
cprintf("log size %d/%d\n", log.lh.n, LOGSIZE);
}
b->flags |= B_DIRTY; // prevent eviction
}
//PAGEBREAK!