On 31/03/22 9:07 pm, Sean Christopherson wrote:
On Thu, Mar 31, 2022, Shivam Kumar wrote:
+ if (!dirty_quota || (pages_dirtied < dirty_quota))
+ return 1;
I don't love returning 0/1 from a function that suggests it returns a bool, but
I do agree it's better than actually returning a bool. I also don't have a better
name, so I'm just whining in the hope that Paolo or someone else has an idea :-)
I've seen plenty of check functions returning 0/1 but please do let me know
if there's a convention to use a bool in such scenarios.
The preferred style for KVM is to return a bool for helpers that are obviously
testing something, e.g. functions with names is "is_valid", "check_request", etc...
But we also very strongly prefer not returning bools from functions that have
side effects or can fail, i.e. don't use a bool to indicate success.
KVM has a third, gross use case of 0/1, where 0 means "exit to userspace" and 1
means "re-enter the guest". Unfortunately, it's so ubiquitous that replacing it
with a proper enum is all but guaranteed to introduce bugs, and the 0/1 behavior
allows KVM to do things liek "if (!some_function())".
This helper falls into this last category of KVM's special 0/1 handling. The
reason I don't love the name is the "check" part, which also puts it into "this
is a check helper". But returning a bool would be even worse because the helper
does more than just check the quota, it also fills in the exit reason.
Does kvm_vcpu_exit_on_dirty_quota_reached make sense? We will invert the
output: 1 will mean "exit to userspace" and 0 will mean "re-enter the
guest". This is verbose but this is the best I could think of.
