10:42 a.m.
sga (or "sgabios" or "Serial Graphics Adapter") is an option ROM for
seabios which directs output to the serial adapter. This is very
useful for debugging BIOS problems during boot.
RHEL wants to deprecate this feature (in fact, they just deprecated it
without telling us). However there is an equivalent feature now in
seabios which can be enabled using either -nographic or
-machine graphics=off
This commit removes sga and enables -machine graphics=off in the
direct backend.
(We cannot do the same for the libvirt backend because libvirt has no
feature to implement this yet).
---
lib/launch-direct.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/lib/launch-direct.c b/lib/launch-direct.c
index 972e77e13..e5b9a5611 100644
--- a/lib/launch-direct.c
+++ b/lib/launch-direct.c
@@ -544,6 +544,13 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
append_list ("gic-version=host");
#endif
append_list_format ("accel=%s", accel_val);
+#if defined(__i386__) || defined(__x86_64__)
+ /* Tell seabios to send debug messages to the serial port.
+ * This used to be done by sgabios.
+ */
+ if (g->verbose)
+ append_list ("graphics=off");
+#endif
} end_list ();
cpu_model = guestfs_int_get_cpu_model (has_kvm && !force_tcg);
@@ -665,18 +672,6 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
} end_list ();
#endif
- if (g->verbose &&
- guestfs_int_qemu_supports_device (g, data->qemu_data,
- "Serial Graphics Adapter")) {
- /* Use sgabios instead of vgabios. This means we'll see BIOS
- * messages on the serial port, and also works around this bug
- * in qemu 1.1.0:
- * https://bugs.launchpad.net/qemu/+bug/1021649
- * QEmu has included sgabios upstream since just before 1.0.
- */
- arg ("-device", "sga");
- }
-
/* Set up virtio-serial for the communications channel. */
start_list ("-chardev") {
append_list ("socket");
--
2.32.0
6:11 a.m.
On 09/08/21 17:42, Richard W.M. Jones wrote:
sga (or "sgabios" or "Serial Graphics Adapter")
is an option ROM for
seabios which directs output to the serial adapter. This is very
useful for debugging BIOS problems during boot.
RHEL wants to deprecate this feature (in fact, they just deprecated it
without telling us). However there is an equivalent feature now in
seabios which can be enabled using either -nographic or
-machine graphics=off
(
That's from SeaBIOS commit 0ebc29f9c4db ("paravirt: serial console
configuration.", 2017-09-22), as far as I can tell. The containing
series is:
1 44270bc1d285 std: add cp437 to unicode map
2 90fa51152714 kbd: make enqueue_key public, add ascii_to_keycode
3 1bda724cc567 romfile: add support for constant files.
4 0ebc29f9c4db paravirt: serial console configuration.
5 d6728f301d7e add serial console support
Part of "rel-1.11.0".
)
This commit removes sga and enables -machine graphics=off in the
direct backend.
(We cannot do the same for the libvirt backend because libvirt has no
feature to implement this yet).
---
lib/launch-direct.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/lib/launch-direct.c b/lib/launch-direct.c
index 972e77e13..e5b9a5611 100644
--- a/lib/launch-direct.c
+++ b/lib/launch-direct.c
@@ -544,6 +544,13 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
append_list ("gic-version=host");
#endif
append_list_format ("accel=%s", accel_val);
+#if defined(__i386__) || defined(__x86_64__)
+ /* Tell seabios to send debug messages to the serial port.
+ * This used to be done by sgabios.
+ */
+ if (g->verbose)
+ append_list ("graphics=off");
+#endif
} end_list ();
cpu_model = guestfs_int_get_cpu_model (has_kvm && !force_tcg);
@@ -665,18 +672,6 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
} end_list ();
#endif
- if (g->verbose &&
- guestfs_int_qemu_supports_device (g, data->qemu_data,
- "Serial Graphics Adapter")) {
- /* Use sgabios instead of vgabios. This means we'll see BIOS
- * messages on the serial port, and also works around this bug
- * in qemu 1.1.0:
- * https://bugs.launchpad.net/qemu/+bug/1021649
- * QEmu has included sgabios upstream since just before 1.0.
- */
- arg ("-device", "sga");
- }
-
/* Set up virtio-serial for the communications channel. */
start_list ("-chardev") {
append_list ("socket");
So, I'm asking this question mainly for my own education:
How does libguestfs deal with different QEMU versions / QEMU feature
deprecation? Is there some kind of feature detection?
For example, why would it be less good to implement the change as follows:
if (g->verbose) {
if (guestfs_int_qemu_supports_device(...) {
arg ("-device", "sga");
} else {
#if defined(__i386__) || defined(__x86_64__)
arg ("-machine", "graphics=off");
#endif
}
This would continue working with SeaBIOS preceding "rel-1.11.0", if at
the same time, the QEMU board had SGA support.
But: do we care? (That's what I'd like to learn about libguestfs,
primarily.)
The patch looks good to me, otherwise.
Reviewed-by: Laszlo Ersek <lersek(a)redhat.com>
Thanks
Laszlo
6:35 a.m.
On Thu, Sep 09, 2021 at 01:11:09PM +0200, Laszlo Ersek wrote:
How does libguestfs deal with different QEMU versions / QEMU feature
deprecation? Is there some kind of feature detection?
Kind of, but it's only grepping the output of -help, -device \?,
and/or looking at QMP output of "query-qmp-schema" and "query-kvm".
The code is in:
https://github.com/libguestfs/libguestfs/blob/master/lib/qemu.c
As qemu has settled down over time and libguestfs uses only a
well-established set of features, this kind of feature detection has
become less and less interesting. (So quite unlike libvirt where
they're always trying to catch up with the latest qemu features). At
some point we might just say "use qemu >= VERSION" and have done with it.
For example, why would it be less good to implement the change as
follows:
if (g->verbose) {
if (guestfs_int_qemu_supports_device(...) {
arg ("-device", "sga");
} else {
#if defined(__i386__) || defined(__x86_64__)
arg ("-machine", "graphics=off");
#endif
}
I think in this case it's my understanding that the "new" (from RHEL 7!)
seabios graphics feature is just better than SGA, and so we might as
well use it all the time even if SGA is available. That was my
understanding from talking to Gerd anyhow.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines. Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top
6:40 a.m.
On Thu, Sep 09, 2021 at 12:35:12PM +0100, Richard W.M. Jones wrote:
On Thu, Sep 09, 2021 at 01:11:09PM +0200, Laszlo Ersek wrote:
> How does libguestfs deal with different QEMU versions / QEMU feature
> deprecation? Is there some kind of feature detection?
Kind of, but it's only grepping the output of -help, -device \?,
and/or looking at QMP output of "query-qmp-schema" and "query-kvm".
The code is in:
https://github.com/libguestfs/libguestfs/blob/master/lib/qemu.c
As qemu has settled down over time and libguestfs uses only a
well-established set of features, this kind of feature detection has
become less and less interesting. (So quite unlike libvirt where
they're always trying to catch up with the latest qemu features). At
some point we might just say "use qemu >= VERSION" and have done with it.
> For example, why would it be less good to implement the change as follows:
>
> if (g->verbose) {
> if (guestfs_int_qemu_supports_device(...) {
> arg ("-device", "sga");
> } else {
> #if defined(__i386__) || defined(__x86_64__)
> arg ("-machine", "graphics=off");
> #endif
> }
I think in this case it's my understanding that the "new" (from RHEL 7!)
seabios graphics feature is just better than SGA, and so we might as
well use it all the time even if SGA is available. That was my
understanding from talking to Gerd anyhow.
IIUC, functionally they should be no difference.
The "better" comes from the seabios impl being written in C
while the sgabios impl is 2500 lines of asm :-)
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
7:06 a.m.
On 09/09/21 13:35, Richard W.M. Jones wrote:
On Thu, Sep 09, 2021 at 01:11:09PM +0200, Laszlo Ersek wrote:
> How does libguestfs deal with different QEMU versions / QEMU feature
> deprecation? Is there some kind of feature detection?
Kind of, but it's only grepping the output of -help, -device \?,
and/or looking at QMP output of "query-qmp-schema" and "query-kvm".
The code is in:
https://github.com/libguestfs/libguestfs/blob/master/lib/qemu.c
As qemu has settled down over time and libguestfs uses only a
well-established set of features, this kind of feature detection has
become less and less interesting. (So quite unlike libvirt where
they're always trying to catch up with the latest qemu features). At
some point we might just say "use qemu >= VERSION" and have done with
it.
OK!
> For example, why would it be less good to implement the change as
> follows:
>
> if (g->verbose) {
> if (guestfs_int_qemu_supports_device(...) {
> arg ("-device", "sga");
> } else {
> #if defined(__i386__) || defined(__x86_64__)
> arg ("-machine", "graphics=off");
> #endif
> }
I think in this case it's my understanding that the "new" (from RHEL
7!)
Ah, OK! I didn't check.
seabios graphics feature is just better than SGA,
Agreed.
and so we might as well use it all the time even if SGA is
available.
That was my understanding from talking to Gerd anyhow.
So yes, my R-b stands. Thanks!
Laszlo
6:22 a.m.
On Wed, Sep 08, 2021 at 04:42:05PM +0100, Richard W.M. Jones wrote:
sga (or "sgabios" or "Serial Graphics Adapter")
is an option ROM for
seabios which directs output to the serial adapter. This is very
useful for debugging BIOS problems during boot.
RHEL wants to deprecate this feature (in fact, they just deprecated it
without telling us). However there is an equivalent feature now in
seabios which can be enabled using either -nographic or
-machine graphics=off
FWIW, this is available since SeaBIOS 1.11, bundled with
QEMU 2.11.0 which is the minimum libvirt supports these
days. I presume libguestfs min version exceeds that ?
This commit removes sga and enables -machine graphics=off in the
direct backend.
(We cannot do the same for the libvirt backend because libvirt has no
feature to implement this yet).
You likely won't need any changes to libvirt side. Once I fully confirm
that it has no impact on live migration, we'll transparentely update
libvirt to use the new syntax.
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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