Messages in this thread | | | Subject | Re: [RFC PATCH 2/4] mm: shmem: Support case-insensitive file name lookups | From | André Almeida <> | Date | Wed, 24 Mar 2021 17:44:25 -0300 |
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Hi Al Viro,
Às 20:19 de 23/03/21, Al Viro escreveu: > On Tue, Mar 23, 2021 at 04:59:39PM -0300, André Almeida wrote: > >> * dcache handling: >> >> 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.
Right, I'll reword this to reflect that there's no expectation that this will be done, while keeping documented this performance issue.
> >> 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... >
Thanks for pointing those issues. I'll move my lock at IOCTL to make impossible to change directory attributes and add a file there at the same time. About the negative dentries that existed before at that directory, I believe the way to solve this is by invalidating them all. How that sound to you?
Thanks, André
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