linux-kernel - Re: [PATCH v6 9/9] ovl: Support mounting case-insensitive enabled layers

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Message-ID: <62e60933-1c43-40c2-a166-91dd27b0e581@igalia.com>
Date: Fri, 22 Aug 2025 13:47:14 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Amir Goldstein <amir73il@...il.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, Theodore Tso <tytso@....edu>,
 Gabriel Krisman Bertazi <krisman@...nel.org>, linux-unionfs@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 kernel-dev@...lia.com
Subject: Re: [PATCH v6 9/9] ovl: Support mounting case-insensitive enabled
 layers

Em 22/08/2025 13:34, Amir Goldstein escreveu:
> On Fri, Aug 22, 2025 at 4:17 PM André Almeida <andrealmeid@...lia.com> wrote:
>>
>> Drop the restriction for casefold dentries lookup to enable support for
>> case-insensitive layers in overlayfs.
>>
>> Support case-insensitive layers with the condition that they should be
>> uniformly enabled across the stack and (i.e. if the root mount dir has
>> casefold enabled, so should all the dirs bellow for every layer).
>>
>> Reviewed-by: Amir Goldstein <amir73il@...il.com>
>> Signed-off-by: André Almeida <andrealmeid@...lia.com>
>> ---
>> Changes from v5:
>> - Fix mounting layers without casefold flag
>> ---
>>   fs/overlayfs/namei.c | 17 +++++++++--------
>>   fs/overlayfs/util.c  | 10 ++++++----
>>   2 files changed, 15 insertions(+), 12 deletions(-)
>>
>> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
>> index 76d6248b625e7c58e09685e421aef616aadea40a..e93bcc5727bcafdc18a499b47a7609fd41ecaec8 100644
>> --- a/fs/overlayfs/namei.c
>> +++ b/fs/overlayfs/namei.c
>> @@ -239,13 +239,14 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
>>          char val;
>>
>>          /*
>> -        * We allow filesystems that are case-folding capable but deny composing
>> -        * ovl stack from case-folded directories. If someone has enabled case
>> -        * folding on a directory on underlying layer, the warranty of the ovl
>> -        * stack is voided.
>> +        * We allow filesystems that are case-folding capable as long as the
>> +        * layers are consistently enabled in the stack, enabled for every dir
>> +        * or disabled in all dirs. If someone has modified case folding on a
>> +        * directory on underlying layer, the warranty of the ovl stack is
>> +        * voided.
>>           */
>> -       if (ovl_dentry_casefolded(base)) {
>> -               warn = "case folded parent";
>> +       if (ofs->casefold != ovl_dentry_casefolded(base)) {
>> +               warn = "parent wrong casefold";
>>                  err = -ESTALE;
>>                  goto out_warn;
>>          }
>> @@ -259,8 +260,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
>>                  goto out_err;
>>          }
>>
>> -       if (ovl_dentry_casefolded(this)) {
>> -               warn = "case folded child";
>> +       if (ofs->casefold != ovl_dentry_casefolded(this)) {
>> +               warn = "child wrong casefold";
>>                  err = -EREMOTE;
>>                  goto out_warn;
>>          }
>> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
>> index a33115e7384c129c543746326642813add63f060..52582b1da52598fbb14866f8c33eb27e36adda36 100644
>> --- a/fs/overlayfs/util.c
>> +++ b/fs/overlayfs/util.c
>> @@ -203,6 +203,8 @@ void ovl_dentry_init_flags(struct dentry *dentry, struct dentry *upperdentry,
>>
>>   bool ovl_dentry_weird(struct dentry *dentry)
>>   {
>> +       struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
>> +
>>          if (!d_can_lookup(dentry) && !d_is_file(dentry) && !d_is_symlink(dentry))
>>                  return true;
>>
>> @@ -210,11 +212,11 @@ bool ovl_dentry_weird(struct dentry *dentry)
>>                  return true;
>>
>>          /*
>> -        * Allow filesystems that are case-folding capable but deny composing
>> -        * ovl stack from case-folded directories.
>> +        * Exceptionally for layers with casefold, we accept that they have
>> +        * their own hash and compare operations
>>           */
>> -       if (sb_has_encoding(dentry->d_sb))
>> -               return IS_CASEFOLDED(d_inode(dentry));
>> +       if (ofs->casefold)
>> +               return false;
> 
> I think this is better as:
>          if (sb_has_encoding(dentry->d_sb))
>                  return false;
> 
> I don't think there is a reason to test ofs->casefold here.
> a "weird" dentry is one that overlayfs doesn't know how to
> handle. Now it known how to handle dentries with hash()/compare()
> on casefolding capable filesysytems.
> 
> Can you please push v6 after this fix to your gitlab branch?
> 

Ok, it's done