Although it seems to be stable with the current Go versions,
unsafe.Pointers that are created by applying arithmetic on nil
pointers are explicitly not allowed[1], and could potentially lead to
panics by the garbage collector. To be on the safe side, this change
goes back to minimal inline wrappers for the callback registrations,
which should be zero-cost. For the callbacks themselves fortunately
no wrappers are required, because CGo happily converts void* to
uintptr arguments. The potentially problematic VoidPtr helper is
removed again.
[1] https://golang.org/pkg/unsafe/#Pointer
Signed-off-by: Sven Anderson <sven@redhat.com>
Since the index of the registered callbacks is basically only used as
void*/unsafe.Pointer, it makes more sense and code simpler, if
the index type is uintptr instead of a simple int.
Signed-off-by: Sven Anderson <sven@redhat.com>
This patch changes the name to the as-agreed-upon naming from a call.
I forgot to fix this in the original patches before merging things.
Oops.
Signed-off-by: John Mulligan <jmulligan@redhat.com>
Previously, the code that set up the callbacks was doing a pretty
direct translation of go-function to c-function. It turns out this
is not needed due to the way we set up the "dynamic" go callbacks
via an integer based callback "registry". Instead, we can stay within
the C layer entirely for the C callback, passing it only the index
value and then return to the go layer through a static C function
that only needs the index value.
Signed-off-by: John Mulligan <jmulligan@redhat.com>
Add UpdateWatch function implementing rbd_update_watch.
Add Unwatch function implementing rbd_update_unwatch.
Add a higher level Watch type to encapsulate watching
the image and the watch handle.
Add basic tests to validate the callback behavior.
Signed-off-by: John Mulligan <jmulligan@redhat.com>
Checking if there are other clients interested in changes to an RBD
image is important for certain actions. For example, the Ceph-CSI
project would not want to remove an image in case it is still mounted
somewhere.
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Sven Anderson
John Mulligan
Niels de Vos