[Libguestfs] [nbdkit PATCH] captive: Support $uri in --run

[Martin Kletzander]

On Tue, Jun 25, 2019 at 09:35:11PM -0500, Eric Blake wrote:
>The existing --run '$nbd' outputs an older form that differs between
>libguestfs and qemu, and which is not always a valid URI.  For
>historical compatibility, we probably can't change that; but we can
>instead add a new '$uri' that outputs a valid URI.  Note that the
>libguestfs '$nbd' TCP form is already a valid URI, but that libguestfs
>still needs to be taught about the nbd+unix:// scheme, so for there,
>you are still better off using '$nbd'; but for qemu, using '$uri'
>already works since qemu v1.3.0 in 2012.
>
>Note that the NBD project has not actually yet posted a link for the
>preferred URI syntax; once Rich is happy with his work on that
>project, we can touch this up to link to that page.
>
>Reported-by: Martin Kletzander <mkletzan at redhat.com>
>Signed-off-by: Eric Blake <eblake at redhat.com>
>---
> docs/nbdkit-captive.pod |  8 +++++++-
> server/captive.c        | 14 +++++++++++++-
> 2 files changed, 20 insertions(+), 2 deletions(-)
>

Looks good to me, thanks.  I haven't even though of this solution =)

Reviewed-by: Martin Kletzander <mkletzan at redhat.com>

>diff --git a/docs/nbdkit-captive.pod b/docs/nbdkit-captive.pod
>index 6f69cca5..59df6690 100644
>--- a/docs/nbdkit-captive.pod
>+++ b/docs/nbdkit-captive.pod
>@@ -42,9 +42,15 @@ The following shell variables are available in the I<--run> argument:
>
> =over 4
>
>+=item C<$uri>
>+
>+A URI that refers to the nbdkit port or socket in the preferred form
>+documented by the NBD project.
>+
> =item C<$nbd>
>
>-A URL that refers to the nbdkit port or socket.
>+An older URL that refers to the nbdkit port or socket in a manner
>+specific to certain tools.
>
> Note there is some magic here, since qemu and guestfish URLs have a
> different format, so nbdkit tries to guess which you are running.  If
>diff --git a/server/captive.c b/server/captive.c
>index 6971af2e..c5274f65 100644
>--- a/server/captive.c
>+++ b/server/captive.c
>@@ -66,7 +66,19 @@ run_command (void)
>     exit (EXIT_FAILURE);
>   }
>
>-  /* Construct $nbd "URL".  Unfortunately guestfish and qemu take
>+  /* Construct $uri. */
>+  fprintf (fp, "uri=");
>+  if (port) {
>+    fprintf (fp, "nbd://localhost:");
>+    shell_quote (port, fp);
>+  }
>+  else if (unixsocket) {
>+    fprintf (fp, "nbd+unix://\\?socket=");
>+    shell_quote (unixsocket, fp);
>+  }
>+  fprintf (fp, "\n");
>+
>+  /* Construct older $nbd "URL".  Unfortunately guestfish and qemu take
>    * different syntax, so try to guess which one we need.
>    */
>   fprintf (fp, "nbd=");
>-- 
>2.20.1
>
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