On Tue, Mar 23, 2021 at 04:59:39PM -0300, André Almeida wrote: > * dcache handling: > > For a +F directory, tmpfs only stores the first equivalent name dentry > used in the dcache. This is done to prevent unintentional duplication of > dentries in the dcache, while also allowing the VFS code to quickly find > the right entry in the cache despite which equivalent string was used in > a previous lookup, without having to resort to ->lookup(). > > d_hash() of casefolded directories is implemented as the hash of the > casefolded string, such that we always have a well-known bucket for all > the equivalencies of the same string. d_compare() uses the > utf8_strncasecmp() infrastructure, which handles the comparison of > equivalent, same case, names as well. > > For now, negative lookups are not inserted in the dcache, since they > would need to be invalidated anyway, because we can't trust missing file > dentries. This is bad for performance but requires some leveraging of > the VFS layer to fix. We can live without that for now, and so does > everyone else. "For now"? Not a single practical suggestion has ever materialized. Pardon me, but by now I'm very sceptical about the odds of that ever changing. And no, I don't have any suggestions either. > The lookup() path at tmpfs creates negatives dentries, that are later > instantiated if the file is created. In that way, all files in tmpfs > have a dentry given that the filesystem exists exclusively in memory. > As explained above, we don't have negative dentries for casefold files, > so dentries are created at lookup() iff files aren't casefolded. Else, > the dentry is created just before being instantiated at create path. > At the remove path, dentries are invalidated for casefolded files. Umm... What happens to those assertions if previously sane directory gets case-buggered? You've got an ioctl for doing just that... Incidentally, that ioctl is obviously racy - result of that simple_empty() might have nothing to do with reality before it is returned to caller. And while we are at it, simple_empty() doesn't check a damn thing about negative dentries in there...
