Libguestfs - Feb 2020 - Re: [PATCH v2] launch: add support for autodetection of appliance image format

On Tue, Jun 27, 2017 at 07:42:20PM +0300, Pavel Butsykin
wrote:
> This feature allows you to use different image formats for the fixed
> appliance. The raw format is used by default.
I wonder if you're stil using this feature?

Unfortunately because of a recent change in libvirt it is no longer
possible to have a backing file where libvirt will autodetect the
format.  See:

https://bugzilla.redhat.com/show_bug.cgi?id=1798148#c3

Therefore the only way to actually do this now would be either for
libguestfs to detect the format (there is an API for this:
guestfs_disk_format), or else to hard code the format in the
./configure option.

In any case I will need to revert this until we can think of something
else (if you still need the feature) because it will simply break with
libvirt >= 6.0.

Rich.
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  lib/launch-direct.c     |  2 ++
>  lib/launch-libvirt.c    | 19 ++++++++++++-------
>  m4/guestfs_appliance.m4 | 11 +++++++++++
>  3 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/launch-direct.c b/lib/launch-direct.c
> index 0be662e25..b9b54857a 100644
> --- a/lib/launch-direct.c
> +++ b/lib/launch-direct.c
> @@ -592,7 +592,9 @@ launch_direct (guestfs_h *g, void *datav, const char
*arg)
>        append_list ("id=appliance");
>        append_list ("cache=unsafe");
>        append_list ("if=none");
> +#ifndef APPLIANCE_FMT_AUTO
>        append_list ("format=raw");
> +#endif
>      } end_list ();
>      start_list ("-device") {
>        append_list ("scsi-hd");
> diff --git a/lib/launch-libvirt.c b/lib/launch-libvirt.c
> index 4adb2cfb3..030ea6911 100644
> --- a/lib/launch-libvirt.c
> +++ b/lib/launch-libvirt.c
> @@ -212,9 +212,10 @@ get_source_format_or_autodetect (guestfs_h *g, struct
drive *drv)
>  
>  /**
>   * Create a qcow2 format overlay, with the given C<backing_drive>
> - * (file).  The C<format> parameter, which must be non-NULL, is the
> - * backing file format.  This is used to create the appliance overlay,
> - * and also for read-only drives.
> + * (file).  The C<format> parameter is the backing file format.
> + * The C<format> parameter can be NULL, in this case the backing
> + * format will be determined automatically.  This is used to create
> + * the appliance overlay, and also for read-only drives.
>   */
>  static char *
>  make_qcow2_overlay (guestfs_h *g, const char *backing_drive,
> @@ -223,8 +224,6 @@ make_qcow2_overlay (guestfs_h *g, const char
*backing_drive,
>    char *overlay;
>    struct guestfs_disk_create_argv optargs;
>  
> -  assert (format != NULL);
> -
>    if (guestfs_int_lazy_make_tmpdir (g) == -1)
>      return NULL;
>  
> @@ -232,8 +231,10 @@ make_qcow2_overlay (guestfs_h *g, const char
*backing_drive,
>  
>    optargs.bitmask = GUESTFS_DISK_CREATE_BACKINGFILE_BITMASK;
>    optargs.backingfile = backing_drive;
> -  optargs.bitmask |= GUESTFS_DISK_CREATE_BACKINGFORMAT_BITMASK;
> -  optargs.backingformat = format;
> +  if (format) {
> +    optargs.bitmask |= GUESTFS_DISK_CREATE_BACKINGFORMAT_BITMASK;
> +    optargs.backingformat = format;
> +  }
>  
>    if (guestfs_disk_create_argv (g, overlay, "qcow2", -1,
&optargs) == -1) {
>      free (overlay);
> @@ -461,7 +462,11 @@ launch_libvirt (guestfs_h *g, void *datav, const char
*libvirt_uri)
>  
>    /* Note that appliance can be NULL if using the old-style appliance. */
>    if (appliance) {
> +#ifdef APPLIANCE_FMT_AUTO
> +    params.appliance_overlay = make_qcow2_overlay (g, appliance, NULL);
> +#else
>      params.appliance_overlay = make_qcow2_overlay (g, appliance,
"raw");
> +#endif
>      if (!params.appliance_overlay)
>        goto cleanup;
>    }
> diff --git a/m4/guestfs_appliance.m4 b/m4/guestfs_appliance.m4
> index 81c43879f..4e1ec8135 100644
> --- a/m4/guestfs_appliance.m4
> +++ b/m4/guestfs_appliance.m4
> @@ -139,3 +139,14 @@ AC_SUBST([GUESTFS_DEFAULT_PATH])
>  
>  AC_DEFINE_UNQUOTED([GUESTFS_DEFAULT_PATH],
["$GUESTFS_DEFAULT_PATH"],
>      [Define guestfs default path.])
> +
> +AC_ARG_ENABLE([appliance-fmt-auto],
> +    [AS_HELP_STRING([--enable-appliance-fmt-auto],
> +        [enable autodetection of appliance image format
@<:@default=no@:>@])],
> +        [ENABLE_APPLIANCE_FMT_AUTO="$enableval"],
> +        [ENABLE_APPLIANCE_FMT_AUTO=no])
> +
> +if test "x$ENABLE_APPLIANCE_FMT_AUTO" = "xyes"; then
> +    AC_DEFINE([APPLIANCE_FMT_AUTO], [1],
> +        [Define to 1 if enabled autodetection of appliance image format.])
> +fi
> -- 
> 2.13.0
> 
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-- 
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On Thu, Feb 06, 2020 at 04:16:46PM +0000, Richard W.M. Jones
wrote:
> On Tue, Jun 27, 2017 at 07:42:20PM +0300, Pavel Butsykin wrote:
> > This feature allows you to use different image formats for the fixed
> > appliance. The raw format is used by default.
> 
> I wonder if you're stil using this feature?
> 
> Unfortunately because of a recent change in libvirt it is no longer
> possible to have a backing file where libvirt will autodetect the
> format.  See:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1798148#c3
> 
> Therefore the only way to actually do this now would be either for
> libguestfs to detect the format (there is an API for this:
> guestfs_disk_format), or else to hard code the format in the
> ./configure option.
> 
> In any case I will need to revert this until we can think of something
> else (if you still need the feature) because it will simply break with
> libvirt >= 6.0.
Actually I can think of a way where we wouldn't need to revert this.
However I'm still interested in whether you are using this feature or
not.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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