From: David Howells <dhowells@redhat.com>
In-Reply-To: <4b5b0a92-8a51-e516-b14a-74557b002d71@gmx.com>
References: <4b5b0a92-8a51-e516-b14a-74557b002d71@gmx.com> <20180816130515.GR24025@twin.jikos.cz> <31114.1534417285@warthog.procyon.org.uk> <32208.1534767847@warthog.procyon.org.uk>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: dhowells@redhat.com, dsterba@suse.cz, clm@fb.com,
        linux-btrfs@vger.kernel.org, wqu@suse.de
Subject: Re: Are the btrfs mount options inconsistent?
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Date: Tue, 21 Aug 2018 14:43:35 +0100
Message-ID: <341.1534859015@warthog.procyon.org.uk>
Sender: linux-btrfs-owner@vger.kernel.org

Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:

> But to be more clear, NOSSD shouldn't be a special case.
> In fact currently NOSSD only affects whether we will output the message
> "enabling ssd optimization", no real effect if I didn't miss anything.

That's not quite true.  In:

	if (!btrfs_test_opt(fs_info, NOSSD) &&
	    !fs_info->fs_devices->rotating) {
		btrfs_set_and_info(fs_info, SSD, "enabling ssd optimizations");
	}

the call to btrfs_set_and_info() will turn on SSD.

What this seems to me is that, normally, SSD will be turned on automatically
unless at least one of the devices is a rotating medium - but this appears to
be explicitly suppressed by the NOSSD option.

David