Commenting for clarity

src/sys/resource.rs

@@ -134,6 +134,7 @@ pub fn getrlimit(resource: Resource) -> Result<(Option<rlim_t>, Option<rlim_t>)>
 /// [`Resource`]: enum.Resource.html
 pub fn setrlimit(resource: Resource, soft_limit: Option<rlim_t>, hard_limit: Option<rlim_t>) -> Result<()> {
     let mut rlim: rlimit = unsafe { mem::uninitialized() };
+    // TODO: How do we handle the case where soft_limit isn't Some()?
     rlim.rlim_cur = soft_limit.unwrap_or(RLIM_INFINITY);
     rlim.rlim_max = hard_limit.unwrap_or(RLIM_INFINITY);
 

test/test_resource.rs

@@ -1,5 +1,13 @@
 use nix::sys::resource::{Resource, getrlimit, setrlimit};
 
+/// Tests the RLIMIT_NOFILE functionality of getrlimit(), where the resource RLIMIT_NOFILE refers
+/// to the maximum file descriptor number that can be opened by the process (aka the maximum number
+/// of file descriptors that the process can open, since Linux 4.5).
+///
+/// We first fetch the existing file descriptor maximum values using getrlimit(), then edit the
+/// soft limit to make sure it has a new and distinct value to the hard limit. We then setrlimit()
+/// to put the new soft limit in effect, and then getrlimit() once more to ensure the limits have
+/// been updated.
 #[test]
 pub fn test_resource_limits_nofile() {
     let (soft_limit, hard_limit) = getrlimit(Resource::RLIMIT_NOFILE).unwrap();
@@ -15,6 +23,12 @@ pub fn test_resource_limits_nofile() {
     assert_eq!(new_soft_limit, soft_limit);
 }
 
+/// Tests the RLIMIT_STACK functionality of getrlimit(), where the resource RLIMIT_STACK refers to
+/// the maximum stack size that can be spawned by the current process before SIGSEGV is generated. 
+///
+/// We first save the current stack limits, then newly set the soft limit to the same size as the
+/// hard limit. We check to make sure these limits have been updated properly. We then set the
+/// stack limits back to the original values, and make sure they have been updated properly.
 #[test]
 pub fn test_resource_limits_stack() {
     let (mut soft_limit, hard_limit) = getrlimit(Resource::RLIMIT_STACK).unwrap();