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refactor bget to be more like iget - make it clear that sleep loops

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rsc 2007-08-08 09:50:26 +00:00
parent 9ad44da676
commit 3f98d050e1
1 changed files with 27 additions and 26 deletions
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53
bio.c
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@ -59,7 +59,7 @@ binit(void)
}
}
// Look through buffer cache for block n on device dev.
// Look through buffer cache for sector on device dev.
// If not found, allocate fresh block.
// In either case, return locked buffer.
static struct buf*
@ -69,34 +69,35 @@ bget(uint dev, uint sector)
acquire(&buf_table_lock);
for(;;){
for(b = bufhead.next; b != &bufhead; b = b->next)
if((b->flags & (B_BUSY|B_VALID)) &&
b->dev == dev && b->sector == sector)
break;
loop:
// Try for cached block.
for(b = bufhead.next; b != &bufhead; b = b->next)
if((b->flags & (B_BUSY|B_VALID)) &&
b->dev == dev && b->sector == sector)
break;
if(b != &bufhead){
if(b->flags & B_BUSY){
sleep(buf, &buf_table_lock);
} else {
b->flags |= B_BUSY;
// b->flags &= ~B_VALID; // Force reread from disk
release(&buf_table_lock);
return b;
}
} else {
for(b = bufhead.prev; b != &bufhead; b = b->prev){
if((b->flags & B_BUSY) == 0){
b->flags = B_BUSY;
b->dev = dev;
b->sector = sector;
release(&buf_table_lock);
return b;
}
}
panic("bget: no buffers");
if(b != &bufhead){
if(b->flags & B_BUSY){
sleep(buf, &buf_table_lock);
goto loop;
}
b->flags |= B_BUSY;
// b->flags &= ~B_VALID; // Force reread from disk
release(&buf_table_lock);
return b;
}
// Allocate fresh block.
for(b = bufhead.prev; b != &bufhead; b = b->prev){
if((b->flags & B_BUSY) == 0){
b->flags = B_BUSY;
b->dev = dev;
b->sector = sector;
release(&buf_table_lock);
return b;
}
}
panic("bget: no buffers");
}
// Read buf's contents from disk.