From: "André Almeida" <email@example.com>
To: Al Viro <firstname.lastname@example.org>
Cc: Hugh Dickins <email@example.com>,
Andrew Morton <firstname.lastname@example.org>,
email@example.com, firstname.lastname@example.org, email@example.com,
Daniel Rosenberg <firstname.lastname@example.org>
Subject: Re: [RFC PATCH 2/4] mm: shmem: Support case-insensitive file name lookups
Date: Wed, 24 Mar 2021 17:44:25 -0300 [thread overview]
Message-ID: <email@example.com> (raw)
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?
next prev parent reply other threads:[~2021-03-24 20:44 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-23 19:59 [RFC PATCH 0/4] mm: shmem: Add case-insensitive support for tmpfs André Almeida
2021-03-23 19:59 ` [RFC PATCH 1/4] Revert "libfs: unexport generic_ci_d_compare() and generic_ci_d_hash()" André Almeida
2021-03-23 20:15 ` Matthew Wilcox
2021-03-24 20:09 ` André Almeida
2021-03-23 19:59 ` [RFC PATCH 2/4] mm: shmem: Support case-insensitive file name lookups André Almeida
2021-03-23 20:18 ` Gabriel Krisman Bertazi
2021-03-24 20:17 ` André Almeida
2021-03-23 23:19 ` Al Viro
2021-03-24 20:44 ` André Almeida [this message]
2021-03-23 19:59 ` [RFC PATCH 3/4] mm: shmem: Add IOCTL support for tmpfs André Almeida
2021-03-23 22:15 ` Gabriel Krisman Bertazi
2021-03-23 19:59 ` [RFC PATCH 4/4] docs: tmpfs: Add casefold options André Almeida
2021-03-23 21:58 ` Randy Dunlap
2021-03-25 14:27 ` André Almeida
2021-03-23 22:19 ` Gabriel Krisman Bertazi
2021-03-24 20:47 ` André Almeida
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