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Date: Wed, 12 Nov 2025 15:38:58 +0100
From: hch <hch@lst.de>
To: Ming Lei <ming.lei@redhat.com>
Cc: hch <hch@lst.de>, Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
	"Darrick J. Wong" <djwong@kernel.org>, Jan Kara <jack@suse.cz>,
	Keith Busch <kbusch@kernel.org>, Dave Chinner <david@fromorbit.com>,
	Carlos Maiolino <cem@kernel.org>,
	Christian Brauner <brauner@kernel.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
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	"linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: fall back from direct to buffered I/O when stable writes are
 required
Message-ID: <20251112143858.GA3006@lst.de>
References: <aQTcb-0VtWLx6ghD@kbusch-mbp> <20251031164701.GA27481@lst.de> <kpk2od2fuqofdoneqse2l3gvn7wbqx3y4vckmnvl6gc2jcaw4m@hsxqmxshckpj> <20251103122111.GA17600@lst.de> <20251104233824.GO196370@frogsfrogsfrogs> <20251105141130.GB22325@lst.de> <20251105214407.GN196362@frogsfrogsfrogs> <9530fca4-418d-4415-b365-cad04a06449b@wdc.com> <20251106124900.GA6144@lst.de> <aRSXQKgkV55fFtNG@fedora>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Wed, Nov 12, 2025 at 10:18:40PM +0800, Ming Lei wrote:
> Looks buffer overwrite is actually done by buggy software in guest side,
> why is qemu's trouble? Or will qemu IO emulator write to the IO buffer
> when guest IO is inflight?

It is ultimately caused by the guest.  But just like local software it
is in no way buggy just because you don't like the pattern.