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Re: [Qemu-devel] [PATCH] block: Add support for Secure Shell (ssh) block
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] block: Add support for Secure Shell (ssh) block device. |
Date: |
Tue, 26 Mar 2013 10:37:49 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Mar 25, 2013 at 03:11:37PM +0000, Richard W.M. Jones wrote:
> On Mon, Mar 25, 2013 at 03:36:22PM +0100, Kevin Wolf wrote:
> > You don't have a bdrv_co_flush_to_disk, what does this mean? Is every
> > write immediately flushed to the disk, is the driver unsafe by design,
> > or is this just a missing implementation detail?
>
> Initially there is no .bdrv_co_flush_to_disk because this patch is
> just a proof of concept.
>
> However it does seem likely that a true flush-to-disk operation is not
> possible with sftp. Assuming this is supposed to guarantee that the
> bits have been committed to disk, I don't see anything in the sftp
> protocol that supports that guarantee. It seems to be left up to the
> implementation to do whatever it wants.
>
> Here's the protocol v3 as implemented by OpenSSH:
>
> http://tools.ietf.org/html/draft-ietf-secsh-filexfer-02
>
> and here's the latest version v6 (not implemented by anyone AFAIK):
>
> http://tools.ietf.org/html/draft-ietf-secsh-filexfer-13
>
> if you think you can see anything that I've missed ...
>
> Also I grepped over the source of OpenSSH and there is no call to
> sync(2), fsync(2) or fdatasync(2).
I looked at OpenSSH sftp-server.c to see if open, close, or write do
anything special. They don't.
There's also no 'sync' command in the SFTP protocol.
So unless the underlying filesystem is mounted -o sync, there is no
guarantee that data is safely on disk.
Stefan
- Re: [Qemu-devel] [PATCH] block: Add support for Secure Shell (ssh) block device., (continued)
Re: [Qemu-devel] [PATCH] block: Add support for Secure Shell (ssh) block device., Stefan Hajnoczi, 2013/03/21
- Re: [Qemu-devel] [PATCH] block: Add support for Secure Shell (ssh) block device., Richard W.M. Jones, 2013/03/21
- [Qemu-devel] [PATCH] block/curl: Add support for Secure Shell (ssh/sftp) block device, Richard W.M. Jones, 2013/03/22
- Re: [Qemu-devel] [PATCH] block/curl: Add support for Secure Shell (ssh/sftp) block device, Stefan Hajnoczi, 2013/03/22
- Re: [Qemu-devel] [PATCH] block/curl: Add support for Secure Shell (ssh/sftp) block device, Richard W.M. Jones, 2013/03/25
- Re: [Qemu-devel] [PATCH] block/curl: Add support for Secure Shell (ssh/sftp) block device, Stefan Hajnoczi, 2013/03/25
Re: [Qemu-devel] [PATCH] block: Add support for Secure Shell (ssh) block device., Kevin Wolf, 2013/03/25