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

[Pino Toscano]

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 <ptosc...@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).

> 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

> 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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