[libvirt-users] Determining domain job kind from job stats?
Hi, is there a reliable way to find out to what kind of job does the information returned from virDomainGetJobStats or provided in VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event callback belong to? I'm specifically interested in distinguishing host-to-host migration jobs (e.g. those started by virDomainMigrateToUri* functions) from other jobs. If there is no better way, I'm thinking about examining presence or values of certain fields in the stats. I'd be fine with that as long as I can be sure it's a reliable way to identify the job kind. Thanks, Milan
On Fri, Feb 10, 2017 at 21:50:19 +0100, Milan Zamazal wrote:
Hi, is there a reliable way to find out to what kind of job does the information returned from virDomainGetJobStats or provided in VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event callback belong to?
No, libvirt expects that the caller knows what job it started. All jobs currently reported using virDomainGetJobStats API or VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event are internally implemented as migration in QEMU driver (either to a file or to a network socket), which may confuse any heuristics for detecting the job type from the set of fields returned by libvirt. What is the problem you are trying to solve? Jirka
Jiri Denemark <jdenemar@redhat.com> writes:
On Fri, Feb 10, 2017 at 21:50:19 +0100, Milan Zamazal wrote:
Hi, is there a reliable way to find out to what kind of job does the information returned from virDomainGetJobStats or provided in VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event callback belong to?
No, libvirt expects that the caller knows what job it started. All jobs currently reported using virDomainGetJobStats API or VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event are internally implemented as migration in QEMU driver (either to a file or to a network socket), which may confuse any heuristics for detecting the job type from the set of fields returned by libvirt.
I see, thank you for explanation.
What is the problem you are trying to solve?
There are basically two problems: - When the job completion callback is called, I need to distinguish what kind of job was it to perform the appropriate actions. It would be easier if I knew the job type directly in the callback (no need to coordinate anything), but "external" job tracking is also possible. - If I lost track of my jobs (e.g. because of a crash and restart), I'd like to find out whether a given VM is migrating. Examining the job looked like a good candidate to get the information, but apparently it's not. Again, I can probably arrange things to handle that, but to get the information directly from libvirt (not necessarily via job info) would be easier and more reliable. Thanks, Milan
On Fri, Feb 17, 2017 at 12:38:24 +0100, Milan Zamazal wrote:
Jiri Denemark <jdenemar@redhat.com> writes:
On Fri, Feb 10, 2017 at 21:50:19 +0100, Milan Zamazal wrote:
Hi, is there a reliable way to find out to what kind of job does the information returned from virDomainGetJobStats or provided in VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event callback belong to?
No, libvirt expects that the caller knows what job it started. All jobs currently reported using virDomainGetJobStats API or VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event are internally implemented as migration in QEMU driver (either to a file or to a network socket), which may confuse any heuristics for detecting the job type from the set of fields returned by libvirt.
I see, thank you for explanation.
What is the problem you are trying to solve?
There are basically two problems:
- When the job completion callback is called, I need to distinguish what kind of job was it to perform the appropriate actions. It would be easier if I knew the job type directly in the callback (no need to coordinate anything), but "external" job tracking is also possible.
An immediate answer would be: "don't rely on the completion callback and just check the return value of the API which started the job", but I guess you want it because checking the return value is not possible when the process which started the job is not running anymore as described below.
- If I lost track of my jobs (e.g. because of a crash and restart), I'd like to find out whether a given VM is migrating. Examining the job looked like a good candidate to get the information, but apparently it's not. Again, I can probably arrange things to handle that, but to get the information directly from libvirt (not necessarily via job info) would be easier and more reliable.
Apparently you are talking about peer-to-peer migration, otherwise the migration would be automatically canceled when the process which started it disappears. I'm afraid this is not currently possible in general. You might be able to get something by checking the domain's status, but it won't work in all cases. Jirka
Jiri Denemark <jdenemar@redhat.com> writes:
On Fri, Feb 17, 2017 at 12:38:24 +0100, Milan Zamazal wrote:
Jiri Denemark <jdenemar@redhat.com> writes:
On Fri, Feb 10, 2017 at 21:50:19 +0100, Milan Zamazal wrote:
Hi, is there a reliable way to find out to what kind of job does the information returned from virDomainGetJobStats or provided in VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event callback belong to?
No, libvirt expects that the caller knows what job it started. All jobs currently reported using virDomainGetJobStats API or VIR_DOMAIN_EVENT_ID_JOB_COMPLETED event are internally implemented as migration in QEMU driver (either to a file or to a network socket), which may confuse any heuristics for detecting the job type from the set of fields returned by libvirt.
I see, thank you for explanation.
What is the problem you are trying to solve?
There are basically two problems:
- When the job completion callback is called, I need to distinguish what kind of job was it to perform the appropriate actions. It would be easier if I knew the job type directly in the callback (no need to coordinate anything), but "external" job tracking is also possible.
An immediate answer would be: "don't rely on the completion callback and just check the return value of the API which started the job", but I guess you want it because checking the return value is not possible when the process which started the job is not running anymore as described below.
Well, avoiding using the completion callback is probably OK for me. (In case of the process restart, I don't expect having everything perfectly working, just some basic sanity.)
- If I lost track of my jobs (e.g. because of a crash and restart), I'd like to find out whether a given VM is migrating. Examining the job looked like a good candidate to get the information, but apparently it's not. Again, I can probably arrange things to handle that, but to get the information directly from libvirt (not necessarily via job info) would be easier and more reliable.
Apparently you are talking about peer-to-peer migration,
Yes.
otherwise the migration would be automatically canceled when the process which started it disappears. I'm afraid this is not currently possible in general. You might be able to get something by checking the domain's status, but it won't work in all cases.
Too bad. Could some future libvirt version provide that information? Thank you for clarification, Milan
[Starting to move to the development list.] Milan Zamazal <mzamazal@redhat.com> writes:
Jiri Denemark <jdenemar@redhat.com> writes:
On Fri, Feb 17, 2017 at 12:38:24 +0100, Milan Zamazal wrote:
There are basically two problems:
- When the job completion callback is called, I need to distinguish what kind of job was it to perform the appropriate actions. It would be easier if I knew the job type directly in the callback (no need to coordinate anything), but "external" job tracking is also possible.
An immediate answer would be: "don't rely on the completion callback and just check the return value of the API which started the job", but I guess you want it because checking the return value is not possible when the process which started the job is not running anymore as described below.
Well, avoiding using the completion callback is probably OK for me.
Thinking about it more, it's not very nice: I have to use the callback to get the completed job stats (I'm not guaranteed the domain still exists on the source host when I ask it for the stats explicitly) *and* to track the jobs outside the callback to know whether the callback is related to the type of domain jobs I'm going to handle. Although not absolutely necessary, it would be much nicer if the job type was identified in the callback.
(In case of the process restart, I don't expect having everything perfectly working, just some basic sanity.)
- If I lost track of my jobs (e.g. because of a crash and restart), I'd like to find out whether a given VM is migrating. Examining the job looked like a good candidate to get the information, but apparently it's not. Again, I can probably arrange things to handle that, but to get the information directly from libvirt (not necessarily via job info) would be easier and more reliable.
Apparently you are talking about peer-to-peer migration,
Yes.
otherwise the migration would be automatically canceled when the process which started it disappears. I'm afraid this is not currently possible in general. You might be able to get something by checking the domain's status, but it won't work in all cases.
Too bad. Could some future libvirt version provide that information?
If libvirt provided information about the job type, it would help with several things, for instance: With the callback problem above, with using libvirt as the ultimate single source of information about the VMs, or with handling VMs not running under complete control of a particular piece of software. If some piece of information about a VM is missing from libvirt I need to store it somewhere. Domain metadata is a natural place for that, since it's closely bound to the corresponding VM and keeps libvirt as the ultimate single source of information. But putting there information about migration is weird at best. Based on those thoughts I think libvirt should really provide a simple way to find out whether the VM is migrating to another host and to identify the domain job type in the job completed callback. Is there anything preventing to add that information? Thanks, Milan
On Tue, Feb 21, 2017 at 15:38:22 +0100, Milan Zamazal wrote:
[Starting to move to the development list.]
Milan Zamazal <mzamazal@redhat.com> writes:
Jiri Denemark <jdenemar@redhat.com> writes:
On Fri, Feb 17, 2017 at 12:38:24 +0100, Milan Zamazal wrote:
There are basically two problems:
- When the job completion callback is called, I need to distinguish what kind of job was it to perform the appropriate actions. It would be easier if I knew the job type directly in the callback (no need to coordinate anything), but "external" job tracking is also possible.
An immediate answer would be: "don't rely on the completion callback and just check the return value of the API which started the job", but I guess you want it because checking the return value is not possible when the process which started the job is not running anymore as described below.
Well, avoiding using the completion callback is probably OK for me.
Thinking about it more, it's not very nice: I have to use the callback to get the completed job stats (I'm not guaranteed the domain still exists on the source host when I ask it for the stats explicitly) *and* to track the jobs outside the callback to know whether the callback is related to the type of domain jobs I'm going to handle.
Although not absolutely necessary, it would be much nicer if the job type was identified in the callback.
The job completed event uses type parameters so adding a new parameter describing the just completed job should not be a problem. Jirka
participants (2)
-
Jiri Denemark -
Milan Zamazal