On Wed, Mar 25, 2015 at 3:45 PM, David Howells <dhowells@xxxxxxxxxx> wrote: > Supply two functions to test whether a filesystem's own dentries are positive > or negative (d_really_is_positive() and d_really_is_negative()). > > The problem is that the DCACHE_ENTRY_TYPE field of dentry->d_flags may be > overridden by the union part of a layered filesystem and isn't thus > necessarily indicative of the type of dentry. > > Normally, this would involve a negative dentry (ie. ->d_inode == NULL) having > ->d_layer.lower pointed to a lower layer dentry, DCACHE_PINNING_LOWER set and > the DCACHE_ENTRY_TYPE field set to something other than DCACHE_MISS_TYPE - but > it could also involve, say, a DCACHE_SPECIAL_TYPE being overridden to > DCACHE_WHITEOUT_TYPE if a 0,0 chardev is detected in the top layer. > > However, inside a filesystem, when that fs is looking at its own dentries, it > probably wants to know if they are really negative or not - and doesn't care > about the fallthrough bits used by the union. > > To this end, a filesystem should normally use d_really_is_positive/negative() > when looking at its own dentries rather than d_is_positive/negative() and > should use d_inode() to get at the inode. > > Anyone looking at someone else's dentries (this includes pathwalk) should use > d_is_xxx() and d_backing_inode(). I think this is confusing as hell, there needs to be more consistency in the naming. E.g. d_backing_is_positive() vs. d_is_positive(). I know it's the other way round now, but only with a few users. Also a separate include file might help, that needs explicit including to get the "backing" variants and which would have big fat warnings all over. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
