[libvirt] [PATCH V3 1/5] Add public API virDomainSendSysrq

[Chun Yan Liu]

>>> On 12/19/2014 at 08:03 PM, in message <54941429.8000802 at redhat.com>, John
Ferlan <jferlan at redhat.com> wrote: 

>  
> On 12/19/2014 12:31 AM, Chun Yan Liu wrote: 
> > 
> > 
> >>>> On 12/18/2014 at 01:00 PM, in message 
> > <5492D0080200006600086404 at soto.provo.novell.com>, "Chun Yan Liu" 
> > <cyliu at suse.com> wrote: 
> > 
> >> 
> >>>>> On 12/17/2014 at 06:52 PM, in message <20141217105227.GQ136165 at orkuz.home>, 
> >> Jiri Denemark <jdenemar at redhat.com> wrote: 
> >>> On Wed, Dec 17, 2014 at 16:48:52 +0800, Chunyan Liu wrote: 
> >>>> Add public API virDomainSendSysrq for sending SysRequest key. 
> >>>> 
> >>>> Signed-off-by: Chunyan Liu <cyliu at suse.com> 
> >>>> --- 
> >>>> changes: 
> >>>>    * add 'flags' to the new API 
> >>>>    * change parameter from 'const char *key' to 'char key' 
> >>>>    * change version number from 1.2.11 to 1.2.12 
> >>>> 
> >>>>   include/libvirt/libvirt-domain.h |  3 +++ 
> >>>>   src/driver-hypervisor.h          |  4 ++++ 
> >>>>   src/libvirt-domain.c             | 39 
> >>> +++++++++++++++++++++++++++++++++++++++ 
> >>>>   src/libvirt_public.syms          |  5 +++++ 
> >>>>   4 files changed, 51 insertions(+) 
> >>>> 
> >>>> diff --git a/include/libvirt/libvirt-domain.h 
> >>> b/include/libvirt/libvirt-domain.h 
> >>>> index baef32d..5f72850 100644 
> >>>> --- a/include/libvirt/libvirt-domain.h 
> >>>> +++ b/include/libvirt/libvirt-domain.h 
> >>>> @@ -3526,6 +3526,9 @@ int virDomainGetFSInfo(virDomainPtr dom, 
> >>>>                          virDomainFSInfoPtr **info, 
> >>>>                          unsigned int flags); 
> >>>> 
> >>>> +/* virDomainSendSysrq */ 
> >>>> +int virDomainSendSysrq(virDomainPtr dom, char key, unsigned int flags); 
> >>>> + 
> >>> 
> >>> I think quite a few reviewers (Daniel, Eric, and I) agreed on using an 
> >>> enum instead of char so that the API is more general. 
> >> 
> >> Sorry, I missed this part. I'll update. One left question: 
> >> How about 'virsh sysrq' parameters? What would we expect users to pass? 
> > 
> > Any thoughts on that? 
> >   libxl_send_sysrq 
>  
> Without a virsh.pod in v3 to go with virsh-domain.c, I'm not sure what  
> you had in mind for syntax previously - although it looks like: 
>  
>      virsh sysrq domain [key] 

Thanks for reply. The syntax I'm used previously is: 
#virsh sysrq domain key
key is required. It's just a letter, like 'h', 'c', etc. About which options can we
have, on can refer to the results on guest through sysrq help. (that is, issue
'virsh sysrq domain h' and look at guest kernel message. I think on each guest,
there must be 'h' option, it will print help message.)

>  
> Where if not provided key would be NULL, which doesn't look good for how  
> the code reads now. 

As said above, key is required, it couldn't be NULL, otherwise, it will report error.

> The description for key in virDomainSendSysrq is  
> still not sufficient to help me either: 
>  
> + * @key:    SysRq key, like h, c, ... 
>  
> What does 'h', 'c', ... mean?  What are the options? What do they map to  
> functionality wise?  I assume it's hypervisor dependent, but that's all  
> stuff you need to describe somewhere. I don't want to guess or go  
> searching for the answer through numerous search engine hits. 

I can add more description on how one could get those options, but the way
I think is through 'sysrq help' and check guest message.

>  
> Looking at the enum Jirka proposed: 
>  
> typedef enum { 
>      VIR_DOMAIN_SYSRQ_REBOOT, 
>      VIR_DOMAIN_SYSRQ_CRASH, 
>      VIR_DOMAIN_SYSRQ_OOM_KILL, 
>      VIR_DOMAIN_SYSRQ_SYNC, 
>      ... 
> } virDomainSysrqCommand; 
>  
> It seems "REBOOT" would/could be the default. So if key wasn't provided  
> the incoming key would be "0" (zero)... If you didn't want a default,  
> then you'd have to force a style to be chosen. You're defining the API  
> so you show us how you want to handle that. Eventually, each hypervisor  
> would map that enum into a character. That is, you'll end up with a way  
> to map the enum to a letter for the types of sysrq's each hypervisor  
> could support. If a hypervisor doesn't support a specific type of sysrq,  
> then decide how to handle. 
>  
> Anyway given the above enum list, I would think the virsh would be: 
>  
>      virsh sysrq domain reboot 
>      virsh sysrq domain crash 
>      virsh sysrq domain kill 
>      virsh sysrq domain sync 
>      ... 

OK. That's what I'm concerned and why I hesitated to change API parameter
from 'char key' to 'enum'. Personally I don't think this is a better user
interface and has risk to miss some functionality, since we don't know
which options those hypervisors can support.

I still prefer: 
#virsh sysrq domain key_letter
One can first issue 'virsh sysrq domain h', and check guest kernel message
for all sysrq options. Then send option as he need.
And as a result, I still think I don't see benefit of changing the API parameter
from 'char key' to 'enum'.

How do you think?

Chunyan

> And key goes from optional to required unless you want to allow 'virsh  
> sysrq domain' to mean reboot by default (e.g., if not provided the  
> default is to reboot). 
>  
> The string for key would be passed to the virDomainSendSysrq which would  
> then "convert" or map that string into an enum. Check out the  
> VIR_ENUM_{IMPL|DECL} usage and how they generate "TypeToString" and  
> "TypeFromString" API's to perform the string <-> enum mapping. 
>  
> So there's "some thoughts" for you - hopefully it gives you some ideas. 
>  
> John 
>  
>