From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE78F76055 for ; Wed, 7 Feb 2024 13:04:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707311058; cv=none; b=nJEnDNW0qWBGJMR7FW73gcC2beK1YR/z/9G/WDBqzY/ebWG65rhW8JRZyYoqfboYYWU1UhRbjkmLPyVSla4WOR2GAC//Ktzgih+ZGDKEZZn3acTXgDN3kGhgqKJKq/ejHDalzY6sYZoZYzvWUacz0hwECrLt4LsmNDLvlOxF904= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707311058; c=relaxed/simple; bh=NX8orA+GVnnPwrF0apwCns+C6OpZLx0AleNzR/n5FUs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cO8YtaBeSf0t0X/ygCiW6+cy/89RQqXB5vgQTZ9EPE09xfw+CvNn1rMsUcIr6iNbXntZ7ckuD5C/rZGJX76FbPpy0Ntd6gkHcarnnGp87UYtWimnn+8IojIl8lZWgNuHnS9eSEv4Uxelvcx8YA9BcokAFlwTuhGLlFBrYUr9VqI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Fb/60FrZ; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Fb/60FrZ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707311055; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=L12i3OcGmJi2tYPUezs3YjaVa/gCWzHhD1McLmDOUM8=; b=Fb/60FrZomR7MEKSM5O2426+YaRPc7cS9Vf35F8ehMU5yO+f1J6lKtCRX++C/AoRWYStlU tPRN7k7AEy3KWy5MPoR6JJ3a0l6cy6FoiK7jY48L5f6KklGS010TazbiZmjceA72cbv9TT Cz/PC525TiKQEEbZSbscPmuRz6xSD5M= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-440-OV_Rx9OvMKyeOZ5fiIid2g-1; Wed, 07 Feb 2024 08:04:11 -0500 X-MC-Unique: OV_Rx9OvMKyeOZ5fiIid2g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 450F5862DC8; Wed, 7 Feb 2024 13:04:11 +0000 (UTC) Received: from bfoster (unknown [10.22.32.186]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C87151121312; Wed, 7 Feb 2024 13:04:10 +0000 (UTC) Date: Wed, 7 Feb 2024 08:05:29 -0500 From: Brian Foster To: Kent Overstreet Cc: Dave Chinner , brauner@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jan Kara , Dave Chinner , "Darrick J. Wong" , Theodore Ts'o Subject: Re: [PATCH v2 3/7] fs: FS_IOC_GETUUID Message-ID: References: <20240206201858.952303-1-kent.overstreet@linux.dev> <20240206201858.952303-4-kent.overstreet@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 On Tue, Feb 06, 2024 at 05:37:22PM -0500, Kent Overstreet wrote: > On Wed, Feb 07, 2024 at 09:01:05AM +1100, Dave Chinner wrote: > > On Tue, Feb 06, 2024 at 03:18:51PM -0500, Kent Overstreet wrote: > > > +static int ioctl_getfsuuid(struct file *file, void __user *argp) > > > +{ > > > + struct super_block *sb = file_inode(file)->i_sb; > > > + > > > + if (!sb->s_uuid_len) > > > + return -ENOIOCTLCMD; > > > + > > > + struct fsuuid2 u = { .len = sb->s_uuid_len, }; > > > + memcpy(&u.uuid[0], &sb->s_uuid, sb->s_uuid_len); > > > + > > > + return copy_to_user(argp, &u, sizeof(u)) ? -EFAULT : 0; > > > +} > > > > Can we please keep the declarations separate from the code? I always > > find this sort of implicit scoping of variables both difficult to > > read (especially in larger functions) and a landmine waiting to be > > tripped over. This could easily just be: > > > > static int ioctl_getfsuuid(struct file *file, void __user *argp) > > { > > struct super_block *sb = file_inode(file)->i_sb; > > struct fsuuid2 u = { .len = sb->s_uuid_len, }; > > > > .... > > > > and then it's consistent with all the rest of the code... > > The way I'm doing it here is actually what I'm transitioning my own code > to - the big reason being that always declaring variables at the tops of > functions leads to separating declaration and initialization, and worse > it leads people to declaring a variable once and reusing it for multiple > things (I've seen that be a source of real bugs too many times). > I still think this is of questionable value. I know I've mentioned similar concerns to Dave's here on the bcachefs list, but still have not really seen any discussion other than a bit of back and forth on the handful of generally accepted (in the kernel) uses of this sort of thing for limiting scope in loops/branches and such. I was skimming through some more recent bcachefs patches the other day (the journal write pipelining stuff) where I came across one or two medium length functions where this had proliferated, and I found it kind of annoying TBH. It starts to almost look like there are casts all over the place and it's a bit more tedious to filter out logic from the additional/gratuitous syntax, IMO. That's still just my .02, but there was also previous mention of starting/having discussion on this sort of style change. Is that still the plan? If so, before or after proliferating it throughout the bcachefs code? ;) I am curious if there are other folks in kernel land who think this makes enough sense that they'd plan to adopt it. Hm? Brian > But I won't push that in this patch, we can just keep the style > consistent for now. > > > > +/* Returns the external filesystem UUID, the same one blkid returns */ > > > +#define FS_IOC_GETFSUUID _IOR(0x12, 142, struct fsuuid2) > > > + > > > > Can you add a comment somewhere in the file saying that new VFS > > ioctls should use the "0x12" namespace in the range 142-255, and > > mention that BLK ioctls should be kept within the 0x12 {0-141} > > range? > > Well, if we're going to try to keep the BLK_ and FS_IOC_ ioctls in > separate ranges, then FS_IOC_ needs to move to something else becasue > otherwise BLK_ won't have a way to expand. > > So what else - > > ioctl-number.rst has a bunch of other ranges listed for fs.h, but 0x12 > appears to be the only one without conflicts - all the other ranges seem > to have originated with other filesystems. > > So perhaps I will take Darrick's nak (0x15) suggestion after all. >