| Message ID | 1367842791-30285-3-git-send-email-pranavkumar@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 05/06/2013 07:19:50 AM, Pranavkumar Sawargaonkar wrote: > Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org> > Signed-off-by: Anup Patel <anup.patel@linaro.org> > --- > Documentation/virtual/virtio-spec.txt | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/Documentation/virtual/virtio-spec.txt > b/Documentation/virtual/virtio-spec.txt > index 0d6ec85..3ca38f8 100644 > --- a/Documentation/virtual/virtio-spec.txt > +++ b/Documentation/virtual/virtio-spec.txt > @@ -1927,11 +1927,16 @@ Ports 2 onwards only if > VIRTIO_CONSOLE_F_MULTIPORT is set > ports; configuration fields nr_ports and max_nr_ports are > valid and control virtqueues will be used. > > + VIRTIO_CONSOLE_F_EMERG_WRITE(2) Device has support for emergency > + write. Configuration filed emerg_wr is valid. Emergency? Really? Out of morbid curiosity, what would constitute an _emergency_ in a virtual machine logging context? Rob
Rob Landley <rob@landley.net> writes: > On 05/06/2013 07:19:50 AM, Pranavkumar Sawargaonkar wrote: >> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org> >> Signed-off-by: Anup Patel <anup.patel@linaro.org> >> --- >> Documentation/virtual/virtio-spec.txt | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/Documentation/virtual/virtio-spec.txt >> b/Documentation/virtual/virtio-spec.txt >> index 0d6ec85..3ca38f8 100644 >> --- a/Documentation/virtual/virtio-spec.txt >> +++ b/Documentation/virtual/virtio-spec.txt >> @@ -1927,11 +1927,16 @@ Ports 2 onwards only if >> VIRTIO_CONSOLE_F_MULTIPORT is set >> ports; configuration fields nr_ports and max_nr_ports are >> valid and control virtqueues will be used. >> >> + VIRTIO_CONSOLE_F_EMERG_WRITE(2) Device has support for emergency >> + write. Configuration filed emerg_wr is valid. > > Emergency? > > Really? > > Out of morbid curiosity, what would constitute an _emergency_ in a > virtual machine logging context? Usually, your console device is broken. Or you can't set it up because you can't allocate memory. Or you oops before it is configured. Terminology is a tricky thing, but the nuance here is that you don't want to use this as your main console. It may not do anything. It may drop characters. It's definitely slow. Cheers, Rusty.
Pranavkumar Sawargaonkar <pranavkumar@linaro.org> writes: > Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org> > Signed-off-by: Anup Patel <anup.patel@linaro.org> > --- > Documentation/virtual/virtio-spec.txt | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) OK, I applied this to the lyx master, with three changes: 1) Changed "filed" to "field". 2) Added ", or even acknowledging the feature" after "without initializing virtio queues". 3) Added an initial point to the Device Initialization section: 1. If the VIRTIO_CONSOLE_F_EMERG_WRITE feature is offered, the emerg_wr field of the configuration can be written at any time. Thus it should work for very early boot debugging output as well as catastophic OS failures (eg. virtio ring corruption). Thanks, Rusty. > diff --git a/Documentation/virtual/virtio-spec.txt b/Documentation/virtual/virtio-spec.txt > index 0d6ec85..3ca38f8 100644 > --- a/Documentation/virtual/virtio-spec.txt > +++ b/Documentation/virtual/virtio-spec.txt > @@ -1927,11 +1927,16 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set > ports; configuration fields nr_ports and max_nr_ports are > valid and control virtqueues will be used. > > + VIRTIO_CONSOLE_F_EMERG_WRITE(2) Device has support for emergency > + write. Configuration filed emerg_wr is valid. > + > Device configuration layout The size of the console is supplied > in the configuration space if the VIRTIO_CONSOLE_F_SIZE feature > is set. Furthermore, if the VIRTIO_CONSOLE_F_MULTIPORT feature > is set, the maximum number of ports supported by the device can > - be fetched.struct virtio_console_config { > + be fetched. If VIRTIO_CONSOLE_F_EMERG_WRITE is set then one can > + use emergency write to output single character without initializing > + virtio queues. struct virtio_console_config { > > u16 cols; > > @@ -1941,6 +1946,7 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set > > u32 max_nr_ports; > > + u32 emerg_wr; > }; > > Device Initialization > -- > 1.7.9.5
Hi Rusty, On 13 May 2013 08:22, Rusty Russell <rusty@rustcorp.com.au> wrote: > Pranavkumar Sawargaonkar <pranavkumar@linaro.org> writes: >> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org> >> Signed-off-by: Anup Patel <anup.patel@linaro.org> >> --- >> Documentation/virtual/virtio-spec.txt | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) > > OK, I applied this to the lyx master, with three changes: > 1) Changed "filed" to "field". > 2) Added ", or even acknowledging the feature" after "without > initializing virtio queues". > 3) Added an initial point to the Device Initialization section: > > 1. If the VIRTIO_CONSOLE_F_EMERG_WRITE feature is offered, the > emerg_wr field of the configuration can be written at any time. Thus > it should work for very early boot debugging output as well as > catastophic OS failures (eg. virtio ring corruption). Thanks for applying this patch. Have you also applied first patch ([PATCH V2 1/3] virtio: console: Add emergency writeonly register to config space) with this? (https://lkml.org/lkml/2013/5/6/169) > > Thanks, > Rusty. Thanks, Pranav > >> diff --git a/Documentation/virtual/virtio-spec.txt b/Documentation/virtual/virtio-spec.txt >> index 0d6ec85..3ca38f8 100644 >> --- a/Documentation/virtual/virtio-spec.txt >> +++ b/Documentation/virtual/virtio-spec.txt >> @@ -1927,11 +1927,16 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set >> ports; configuration fields nr_ports and max_nr_ports are >> valid and control virtqueues will be used. >> >> + VIRTIO_CONSOLE_F_EMERG_WRITE(2) Device has support for emergency >> + write. Configuration filed emerg_wr is valid. >> + >> Device configuration layout The size of the console is supplied >> in the configuration space if the VIRTIO_CONSOLE_F_SIZE feature >> is set. Furthermore, if the VIRTIO_CONSOLE_F_MULTIPORT feature >> is set, the maximum number of ports supported by the device can >> - be fetched.struct virtio_console_config { >> + be fetched. If VIRTIO_CONSOLE_F_EMERG_WRITE is set then one can >> + use emergency write to output single character without initializing >> + virtio queues. struct virtio_console_config { >> >> u16 cols; >> >> @@ -1941,6 +1946,7 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set >> >> u32 max_nr_ports; >> >> + u32 emerg_wr; >> }; >> >> Device Initialization >> -- >> 1.7.9.5
diff --git a/Documentation/virtual/virtio-spec.txt b/Documentation/virtual/virtio-spec.txt index 0d6ec85..3ca38f8 100644 --- a/Documentation/virtual/virtio-spec.txt +++ b/Documentation/virtual/virtio-spec.txt @@ -1927,11 +1927,16 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set ports; configuration fields nr_ports and max_nr_ports are valid and control virtqueues will be used. + VIRTIO_CONSOLE_F_EMERG_WRITE(2) Device has support for emergency + write. Configuration filed emerg_wr is valid. + Device configuration layout The size of the console is supplied in the configuration space if the VIRTIO_CONSOLE_F_SIZE feature is set. Furthermore, if the VIRTIO_CONSOLE_F_MULTIPORT feature is set, the maximum number of ports supported by the device can - be fetched.struct virtio_console_config { + be fetched. If VIRTIO_CONSOLE_F_EMERG_WRITE is set then one can + use emergency write to output single character without initializing + virtio queues. struct virtio_console_config { u16 cols; @@ -1941,6 +1946,7 @@ Ports 2 onwards only if VIRTIO_CONSOLE_F_MULTIPORT is set u32 max_nr_ports; + u32 emerg_wr; }; Device Initialization