linux-ext4 - Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on case-insensitive ext4 and f2fs

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Date: Fri, 24 Nov 2023 10:20:39 -0500
From: Gabriel Krisman Bertazi <gabriel@...sman.be>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Gabriel Krisman Bertazi <gabriel@...sman.be>,  Linus Torvalds
 <torvalds@...ux-foundation.org>,  Christian Brauner <brauner@...nel.org>,
  tytso@....edu,  linux-f2fs-devel@...ts.sourceforge.net,
  ebiggers@...nel.org,  linux-fsdevel@...r.kernel.org,  jaegeuk@...nel.org,
  linux-ext4@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH v6 0/9] Support negative dentries on
 case-insensitive ext4 and f2fs

Al Viro <viro@...iv.linux.org.uk> writes:

> On Thu, Nov 23, 2023 at 02:06:39PM -0500, Gabriel Krisman Bertazi wrote:
>
>> > A paragraph above you've said that it's not constant over the entire
>> > filesystem.
>> 
>> The same ->d_op is used by every dentry in the filesystem if the superblock
>> has the casefold bit enabled, regardless of whether a specific inode is
>> casefolded or not. See generic_set_encrypted_ci_d_ops in my tree. It is
>> called unconditionally by ext4_lookup and only checks the superblock:
>> 
>> void generic_set_encrypted_ci_d_ops(struct dentry *dentry)
>> {
>>         if (dentry->d_sb->s_encoding) {
>> 		d_set_d_op(dentry, &generic_encrypted_ci_dentry_ops);
>> 		return;
>> 	}
>>         ...
>> 
>> What I meant was that this used to be set once at sb->s_d_op, and
>> propagated during dentry allocation.  Therefore, the propagation to the
>> alias would happen inside __d_alloc.  Once we enabled fscrypt and
>> casefold to work together, sb->s_d_op is NULL
>
> Why?  That's what I don't understand - if you really want it for
> all dentries on that filesystem, that's what ->s_d_op is for.
> If it is not, you have that problem, no matter which way you flip ->d_op
> value.

I'm not sure why it changed.  I'm guessing that, since it doesn't make
sense to set fscrypt_d_revalidate for every dentry in the
!case-insensitive case, they just kept the same behavior for
case-insensitive+fscrypt.  This is what I get from looking at the git
history.

I will get a new series reverting to use ->s_d_op, folding the
dentry_cmp behavior you mentioned, and based on what you merge in your
branch.

>> and we always set the same
>> handler for every dentry during lookup.
>
> Not every dentry goes through lookup - see upthread for details.

Yes, I got that already.  This should be "we always set the same handler
for every dentry that goes through lookup and bork whatever doesn't come
through lookup."

-- 
Gabriel Krisman Bertazi