On Wed, Mar 27, 2024 at 04:16:31AM -0700, Christoph Hellwig wrote: > On Tue, Mar 26, 2024 at 07:04:50PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > It's possible that the dentry cache can tell us the parent of a > > directory. Therefore, when repairing directory dot dot entries, query > > the dcache as a last resort before scanning the entire filesystem. > > The code looks fine, but how high is the chance that we actually have > a valid dcache entry for a file in a corrupted directory? Decent. Say you have a 1000-block directory foo, and block 980 gets corrupted. Let's further suppose that block 0 has an entry for ".." and "bar". If someone accesses /mnt/foo/bar, won't that cause the dcache to create a dentry from /mnt to /mnt/foo whose d_parent points back to /mnt? If you then want to rebuild the directory, we can obtain the parent from the dcache without needing to wander into parent pointers or scan the filesystem to find /mnt's connection to foo. --D
