Re: [PATCH v2 11/17] xen/hypfs: add getsize() and findentry() callbacks to hypfs_funcs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.12.2020 09:21, Juergen Gross wrote:
> @@ -197,28 +235,12 @@ static struct hypfs_entry *hypfs_get_entry_rel(struct 
> hypfs_entry_dir *dir,
>              end = strchr(path, '\0');
>          name_len = end - path;
>  
> -        again = false;
> +        entry = dir->e.funcs->findentry(dir, path, name_len);
> +        if ( IS_ERR(entry) || !*end )
> +            return entry;
>  
> -        list_for_each_entry ( entry, &dir->dirlist, list )
> -        {
> -            int cmp = strncmp(path, entry->name, name_len);
> -            struct hypfs_entry_dir *d = container_of(entry,
> -                                                     struct hypfs_entry_dir, 
> e);
> -
> -            if ( cmp < 0 )
> -                return ERR_PTR(-ENOENT);
> -            if ( !cmp && strlen(entry->name) == name_len )
> -            {
> -                if ( !*end )
> -                    return entry;
> -
> -                again = true;
> -                dir = d;
> -                path = end + 1;
> -
> -                break;
> -            }
> -        }
> +        path = end + 1;
> +        dir = container_of(entry, struct hypfs_entry_dir, e);
>      }

Looking at patch 15 my understanding is that "dir" may get invalidated
by the call to the ->findentry() hook above. That is, use of dir has
to be avoided between the two calls. This isn't at all obvious, so I
wonder whether at least a comment wouldn't want adding to avoid future
mistakes.

And of course the same comment applies to the IS_ERR() use here vs NULL
coming back that I already gave for the ->enter() call site.

Jan