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Re: [Qemu-devel] [PATCH v3] block: Add support for Secure Shell (ssh) bl
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From: |
Stefan Hajnoczi |
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Subject: |
Re: [Qemu-devel] [PATCH v3] block: Add support for Secure Shell (ssh) block device. |
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Date: |
Tue, 26 Mar 2013 17:23:03 +0100 |
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User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Mar 26, 2013 at 02:21:39PM +0000, Richard W.M. Jones wrote:
> On Tue, Mar 26, 2013 at 10:38:46AM +0000, Richard W.M. Jones wrote:
> > + /* According to the docs, this just updates a field in the
> > + * sftp_handle structure, so there is no network traffic and it
> > + * cannot fail.
> > + */
> > + libssh2_sftp_seek64(s->sftp_handle, offset);
>
> While I was looking at the performance of qemu+ssh vs sshfs, I noticed
> that the line above has a catastrophic effect on performance, since it
> causes all readahead data to be thrown away. Ooops. I'm reworking
> the patch to make seeking more intelligent.
Should libssh2 be smarter and preserve the readahead when offsets are
contiguous?
It makes sense to fix in QEMU for older libssh2 binaries, but the real
fix might be for libssh2 to be smart.
Stefan