On Thu, Sep 01, 2016 at 01:37:17PM -0700, Andrew Morton wrote:
What the heck are the return value semantics of bus_type.online?
Sometimes 0, sometimes 1 and apparently sometimes -Efoo values. What
are these things trying to tell the caller and why is "1" ever useful
and why doesn't anyone document anything. grr.
You might be getting tangled in the two codepaths the way I was.
If you do 'echo 1 > online':
dev_attr_store
online_store
device_online
memory_subsys_online
memory_block_change_state
If you do 'echo online > state':
dev_attr_store
store_mem_state
device_online
memory_subsys_online
memory_block_change_state
static int memory_subsys_online(struct device *dev)
{
struct memory_block *mem = to_memory_block(dev);
int ret;
if (mem->state == MEM_ONLINE)
return 0;
Doesn't that "return 0" contradict the changelog?
The online-to-online check being used is higher in the call chain:
int device_online(struct device *dev)
{
if (device_supports_offline(dev)) {
if (dev->offline) {
...
} else {
ret = 1;
}
}
Also, is store_mem_state() the correct place to fix this? Instead,
should memory_block_change_state() detect an attempt to online
already-online memory and itself return -EINVAL, and permit that to be
propagated back?
Doing that would affect both codepaths, and as David made clear, would
break backwards compatibility because their established behaviors are
different.
'echo 1 > online' returns 0 if the device is already online
'echo online > state' returns -EINVAL if the device is already online
--
Reza Arbab
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