If /sbin/bridge-stp is available on the system, bridge tries to execute
it instead of the kernel implementation when starting/stopping STP.
If anything goes wrong with /sbin/bridge-stp, bridge silently falls back
to kernel STP, making hard to debug userspace STP.
This patch adds a br_stp_call_user helper to start/stop userspace STP
and debug errors from the program: abnormal exit status is stored in the
lower byte and normal exit status is stored in higher byte.
Below is a simple example on a kernel with dynamic debug enabled:
# ln -s /bin/false /sbin/bridge-stp
# brctl stp br0 on
br0: failed to start userspace STP (256)
# dmesg
br0: /sbin/bridge-stp exited with code 1
br0: failed to start userspace STP (256)
br0: using kernel STP
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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