Re: [PATCH 3/3] Xen physical cpus interface

From: Konrad Rzeszutek Wilk
Date: Fri May 11 2012 - 10:34:08 EST

On Fri, May 11, 2012 at 01:12:13PM +0000, Liu, Jinsong wrote:
> Liu, Jinsong wrote:
> > Just notice your reply (so quick :)
> >
> > Agree and will update later, except 1 concern below.
> >
> > Konrad Rzeszutek Wilk wrote:
> >>>
> >>> Hmm, it's good if it's convenient to do it automatically via
> >>> dev->release. However, dev container (pcpu) would be free at some
> >>> other error cases, so I prefer do it 'manually'.
> >>
> >> You could also call pcpu_release(..) to do it manually.
> >>
> >
> > that means kfree(pcpu) would be done twice at some error cases, do
> > you think it really good?
> >
> Ping.
> I think error recovery should be kept inside error logic level itself, if try to recover upper level error would bring trouble.
> In our example, there are 2 logic levels:
> pcpu level (as container), and dev level (subfield used for sys)

So you need to untangle free_pcpu from doing both. Meaning one does the
SysFS and the other deals with free-ing the structure and removing itself
from the list.

> dev->release should only recover error occurred at dev/sys level, and the pcpu error should be recovered at pcpu level.
> If dev->release try to recover its container pcpu level error, like list_del/kfree(pcpu), it would make confusing. i.e., considering pcpu_sys_create(), 2 error cases:
> device_register fail, and device_create_file fail --> how can the caller decide kfree(pcpu) or not?

Then you should free it manually. But you can do this by a wrapper

__pcpu_release(..) {
/* Does the removing itself from the list and kfree the pcpu */
pcpu_release(..) {
struct pcpcu *p= container_of(..)

dev->release = &pcpu_release;

> So how about recover pcpu error manually and explicitly?
> Thanks,
> Jinsong
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