linux-kernel - Re: [PATCH v4 3/9] ovl: Create ovl_casefold() to support casefolded strncmp()

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Message-ID: <CAOQ4uxiYdbr8X5uFxTdqw6ba7E+6KZY0mhQYw2_t875gw4vfiw@mail.gmail.com>
Date: Thu, 14 Aug 2025 15:20:33 +0200
From: Amir Goldstein <amir73il@...il.com>
To: André Almeida <andrealmeid@...lia.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 v4 3/9] ovl: Create ovl_casefold() to support casefolded strncmp()

On Thu, Aug 14, 2025 at 3:02 PM André Almeida <andrealmeid@...lia.com> wrote:
>
> Hi Amir,
>
> Em 14/08/2025 09:53, Amir Goldstein escreveu:
> > On Thu, Aug 14, 2025 at 12:37 AM André Almeida <andrealmeid@...lia.com> wrote:
> >>
> >> To add overlayfs support casefold filesystems, create a new function
> >> ovl_casefold(), to be able to do case-insensitive strncmp().
> >>
> >> ovl_casefold() allocates a new buffer and stores the casefolded version
> >> of the string on it. If the allocation or the casefold operation fails,
> >> fallback to use the original string.
> >>
> >> The case-insentive name is then used in the rb-tree search/insertion
> >> operation. If the name is found in the rb-tree, the name can be
> >> discarded and the buffer is freed. If the name isn't found, it's then
> >> stored at struct ovl_cache_entry to be used later.
> >>
> >> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> >> ---
>
> [...]
>
> >> +       }
> >>
> >>          INIT_LIST_HEAD(list);
> >>   }
> >> @@ -260,12 +311,28 @@ static bool ovl_fill_merge(struct dir_context *ctx, const char *name,
> >>   {
> >>          struct ovl_readdir_data *rdd =
> >>                  container_of(ctx, struct ovl_readdir_data, ctx);
> >> +       struct ovl_fs *ofs = OVL_FS(rdd->dentry->d_sb);
> >> +       const char *aux = NULL;
> >
> > It looks strange to me that you need aux
> > and it looks strange to pair <aux, cf_len>
> > neither here or there...
> >
>
> The reason behind this `aux` var is because I need a `const char`
> pointer to point to the `name` argument, and `cf_name` can't be const
> because it goes through ovl_casefold(). I tried a couple approaches here
> to get rid of the compiler warning regarding const, and the only way I
> managed to was using a third variable like that.
>

I see. In that case, I'd just use these cleaner var names:

@@ -260,12 +311,28 @@ static bool ovl_fill_merge(struct dir_context
*ctx, const char *name,
 {
        struct ovl_readdir_data *rdd =
                container_of(ctx, struct ovl_readdir_data, ctx);
+       struct ovl_fs *ofs = OVL_FS(rdd->dentry->d_sb);
+       char *cf_name = NULL;
+       const char *c_name;
+       int c_len = 0;
+
+       if (ofs->casefold)
+               c_len = ovl_casefold(rdd->map, name, namelen, &cf_name);
+
+       if (c_len <= 0) {
+               c_name = name;
+               c_len = namelen;
+       } else {
+               c_name = cf_name;
+       }

Thanks,
Amir.