linux-kernel - Re: [ANNOUNCE] Native Linux KVM tool v2

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Message-ID: <BANLkTikoMZCFzA6jUw+ddHZ3x2cvO_NzhA@mail.gmail.com>
Date:	Thu, 16 Jun 2011 12:57:36 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Alexander Graf <agraf@...e.de>,
	Prasad Joshi <prasadjoshi124@...il.com>,
	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Sasha Levin <levinsasha928@...il.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Asias He <asias.hejun@...il.com>,
	Jens Axboe <jaxboe@...ionio.com>
Subject: Re: [ANNOUNCE] Native Linux KVM tool v2

On Thu, Jun 16, 2011 at 12:48 PM, Christoph Hellwig <hch@...radead.org> wrote:
> You also missed:
>
> " This system call does not flush disk write caches and thus does not
>  provide any data integrity on systems with volatile disk write
>  caches."
>
> so it's not safe if you either have a cache, or are using btrfs, or
> are using a sparse image, or are using an image preallocated using
> fallocate/posix_fallocate.

Uh-oh. Someone needs to apply this patch to sync_file_range():

diff --git a/fs/sync.c b/fs/sync.c
index ba76b96..32078aa 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -277,6 +277,8 @@ SYSCALL_DEFINE(sync_file_range)(int fd, loff_t
offset, loff_t nbytes,
        int fput_needed;
        umode_t i_mode;

+       WARN_ONCE(1, "when this breaks, you get to keep both pieces");
+
        ret = -EINVAL;
        if (flags & ~VALID_FLAGS)
                goto out;


>> What's the right thing to do here? Is fdatasync() sufficient?
>
> Yes.

We'll fix that up. Thanks Christoph!

                         Pekka
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