diff options
| -rw-r--r-- | bio.c | 6 | ||||
| -rw-r--r-- | fs.c | 15 |
2 files changed, 12 insertions, 9 deletions
@@ -75,9 +75,9 @@ bget(uint dev, uint blockno) } } - // Not cached; recycle some unused buffer and clean buffer - // "clean" because B_DIRTY and not locked means log.c - // hasn't yet committed the changes to the buffer. + // Not cached; recycle an unused buffer. + // Even if refcnt==0, B_DIRTY indicates a buffer is in use + // because log.c has modified it but not yet committed it. for(b = bcache.head.prev; b != &bcache.head; b = b->prev){ if(b->refcnt == 0 && (b->flags & B_DIRTY) == 0) { b->dev = dev; @@ -155,10 +155,10 @@ bfree(int dev, uint b) // have locked the inodes involved; this lets callers create // multi-step atomic operations. // -// The icache.lock spin-lock defends ip->ref, ip->dev, and ip->inum. -// Since ip->ref indicates whether an icache entry is free, the -// icache.lock defends icache allocation. icache.lock also defends -// all fields of an unallocated icache entry, during allocation. +// The icache.lock spin-lock defends the allocation of icache +// entries. Since ip->ref indicates whether an entry is free, +// and ip->dev and ip->inum indicate which i-node an entry +// holds, one must hold icache.lock while using any of those fields. // // An ip->lock sleep-lock defends all ip-> fields other than ref, // dev, and inum. One must hold ip->lock in order to @@ -189,8 +189,9 @@ iinit(int dev) static struct inode* iget(uint dev, uint inum); //PAGEBREAK! -// Allocate a new inode with the given type on device dev. -// A free inode has a type of zero. +// Allocate an inode on device dev. +// Give it type type. +// Returns an unlocked but allocated and referenced inode. struct inode* ialloc(uint dev, short type) { @@ -214,6 +215,8 @@ ialloc(uint dev, short type) } // Copy a modified in-memory inode to disk. +// Must be called after every change to an ip->xxx field +// that lives on disk, since i-node cache is write-through. // Caller must hold ip->lock. void iupdate(struct inode *ip) |