Re: [Qemu-devel] [PATCH] ssh: switch from libssh2 to libssh

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Oct 20, 2016 at 05:44:41PM +0200, Pino Toscano wrote:
> On Thursday, 20 October 2016 16:32:50 CEST Richard W.M. Jones wrote:
> > On Thu, Oct 20, 2016 at 05:15:24PM +0200, Pino Toscano wrote:
> > > Rewrite the implementation of the ssh block driver to use libssh instead
> > > of libssh.  The libssh library has various advantages over libssh:
> > > - easier API for authentication (for example for using ssh-agent)
> > > - easier API for known_hosts handling
> > > - supports newer types of keys in known_hosts
> > > 
> > > Kerberos authentication can be enabled once the libssh bug for it [1] is
> > > fixed.
> > > 
> > > The development version of libssh (i.e. the future 0.8.x) supports
> > > fsync, so reuse the build time check for this.
> > > 
> > > [1] https://red.libssh.org/issues/242
> > > 
> > > Signed-off-by: Pino Toscano <ptoscano@redhat.com>
> > 
> > 
> > When I applied this patch and compiled it with warnings enabled:
> > 
> > block/ssh.c: In function ‘connect_to_ssh’:
> > block/ssh.c:643:12: warning: ‘ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> >      return ret;
> >             ^~~
> 
> Interesting, there was no warning for me.  Anyway, I think this:
> 
> diff --git a/block/ssh.c b/block/ssh.c
> index 7c316db..7ff376e 100644
> --- a/block/ssh.c
> +++ b/block/ssh.c
> @@ -519,6 +519,7 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
>      /* Create SSH session. */
>      s->session = ssh_new();
>      if (!s->session) {
> +        ret = -EINVAL;
>          goto err;
>      }
>  
> should fix it (added already locally).

Yes, this fixes the warning.

> > To test the patch, I used virt-builder to create a virtual machine
> > disk image on another machine (accessible over ssh).  Then from my
> > laptop I ran:
> > 
> >   ./x86_64-softmmu/qemu-system-x86_64 -nodefconfig \
> >       -M accel=kvm -cpu host -m 2048 \
> >       -drive file.driver=ssh,file.user=[user],file.host=[host],file.path=/var/tmp/fedora-24.img,format=raw,if=virtio \
> >       -serial stdio
> > 
> > Unfortunately this failed with a large number of sftp errors:
> > 
> >   read failed: (sftp error code: 0)
> > 
> > and subsequently hung.  So I'm afraid I couldn't test the patch at all :-(
> 
> Can you please enable the logging of the ssh driver, and libssh own
> logging too?  Basically (see lines 45-46) set:
> 
> #define DEBUG_SSH     1
> #define TRACE_LIBSSH  4

I'll send you the full trace privately since it's enormous.

Rich.

> > Also fsync was not supported for me, but I'm using 0.7.3 and the code
> > says I need 0.8.0.
> 
> Yes, this is correct.
> 
> Thanks,
> -- 
> Pino Toscano



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