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Date:   Tue, 17 Dec 2019 17:46:52 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        David Howells <dhowells@redhat.com>,
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        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Phillip Lougher <phillip@squashfs.org.uk>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] vfs: Don't reject unknown parameters
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On Fri, Dec 13, 2019 at 10:15:03AM +0100, Miklos Szeredi wrote:

> Just need a flag in fc indicating if this option comes from the old interface:
> 
>          if (strcmp(param->key, "source") == 0)
>                  return -ENOPARAM;
>          /* Just log an error for backwards compatibility */
>          errorf(fc, "%s: Unknown parameter '%s'", fc->fs_type->name,
> param->key);
>          return fc->legacy ? 0 : -ENOPARAM;

	What the hell for?  Just have a separate ->parse_param() instance
for "promiscuous fs, will accept bullshit options" and have such filesystems
use it explicitly.  With default being not that, but rejecting unknowns.