Re: [Xen-devel] [PATCH v4 2/3] golang/xenlight: Notify xenlight of SIGCHLD

[Nick Rosbrook <rosbrookn@xxxxxxxxx>]

> libxl forks external processes and waits for them to complete; it
> therefore needs to be notified when children exit.
>
> In absence of instructions to the contrary, libxl sets up its own
> SIGCHLD handlers.
>
> Golang always unmasks and handles SIGCHLD itself.  libxl thankfully
> notices this and throws an assert() rather than clobbering SIGCHLD
> handlers.
>
> Tell libxl that we'll be responsible for getting SIGCHLD notifications
> to it.  Arrange for a channel in the context to receive notifications
> on SIGCHLD, and set up a goroutine that will pass these on to libxl.
>
> NB that every libxl context needs a notification; so multiple contexts
> will each spin up their own goroutine when opening a context, and shut
> it down on close.
>
> libxl also wants to hold on to a const pointer to
> xenlight_childproc_hooks rather than do a copy; so make a global
> structure in C space.  Make it `static const`, just for extra safety;
> this requires making a function in the C space to pass it to libxl.
>
> While here, add a few comments to make the context set-up a bit easier
> to follow.
>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>

Reviewed-by: Nick Rosbrook <rosbrookn@xxxxxxxxxxxx>

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