Support for offlined CPUs in /proc/stat (#8193)

Summary:
Pull Request resolved: https://github.com/facebookincubator/below/pull/8193

Currently procfs assumes that no CPUs are offlined. That is not always
the case.

Addresses #8190.

Reviewed By: antonis-m

Differential Revision: D46937378

fbshipit-source-id: 3f21fbd283fb43e4f6c64c4a28e6e756ca23a93e

3 files changed, 21 insertions, 9 deletions

diff --git a/below/procfs/src/lib.rs b/below/procfs/src/lib.rs
index bee9d294..667d04af 100644
--- a/below/procfs/src/lib.rs
+++ b/below/procfs/src/lib.rs
@@ -181,7 +181,7 @@ impl ProcReader {
     }
 
     fn process_cpu_stat(path: &PathBuf, line: &String) -> Result<CpuStat> {
-        //Format is like "cpu9 6124418 452468 3062529 230073290 216237 0 45647 0 0 0"
+        // Format is like "cpu9 6124418 452468 3062529 230073290 216237 0 45647 0 0 0"
         let mut items = line.split_whitespace();
         let mut cpu: CpuStat = Default::default();
 
@@ -215,7 +215,7 @@ impl ProcReader {
         let file = File::open(&path).map_err(|e| Error::IoError(path.clone(), e))?;
         let buf_reader = BufReader::new(file);
         let mut stat: Stat = Default::default();
-        let mut cpus = Vec::new();
+        let mut cpus_map = BTreeMap::new();
         for line in buf_reader.lines() {
             let line = line.map_err(|e| Error::IoError(path.clone(), e))?;
 
@@ -241,15 +241,23 @@ impl ProcReader {
                     x => {
                         if x == "cpu" {
                             stat.total_cpu = Some(Self::process_cpu_stat(&path, &line)?);
-                        } else if x.starts_with("cpu") {
-                            cpus.push(Self::process_cpu_stat(&path, &line)?);
+                        } else if let Some(cpu_suffix) = x.strip_prefix("cpu") {
+                            let cpu_id =
+                                parse_item!(&path, Some(cpu_suffix.to_owned()), u32, line)?
+                                    .unwrap();
+                            let existing =
+                                cpus_map.insert(cpu_id, Self::process_cpu_stat(&path, &line)?);
+                            if existing.is_some() {
+                                return Err(Error::UnexpectedLine(path, line));
+                            }
                         }
                     }
                 }
             }
         }
-        if !cpus.is_empty() {
-            stat.cpus = Some(cpus);
+        if !cpus_map.is_empty() {
+            stat.cpus = Some(cpus_map.values().cloned().collect());
+            stat.cpus_map = Some(cpus_map);
         }
 
         if stat == Default::default() {
diff --git a/below/procfs/src/test.rs b/below/procfs/src/test.rs
index 94e2c703..3d554cd4 100644
--- a/below/procfs/src/test.rs
+++ b/below/procfs/src/test.rs
@@ -160,7 +160,6 @@ cpu18 5917745 448756 3050060 230279037 215704 0 45064 0 0 0
 cpu19 6042834 433710 3058862 230151162 214883 0 45179 0 0 0
 cpu20 5804757 444950 3057184 230372774 224962 0 46132 0 0 0
 cpu21 5935027 455253 3052007 230250433 209736 0 45325 0 0 0
-cpu22 5874699 446579 3061270 230279298 235842 0 45808 0 0 0
 cpu23 5937943 460201 3057286 230166670 230819 0 42628 0 0 0
 intr 29638874355 54 9 0 0 14325 0 0 0 1 0 19 0 5 0 0 0 0 0 0 0 0 0 0 0 0 14 0 109094370 0 464199486 9840 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
 ctxt 48203489122
@@ -189,8 +188,11 @@ softirq 15518280031 0 3506477306 138437 1090758178 117192437 0 24543 800441241 9
 
     assert_eq!(total_cpu.guest_nice_usec, Some(0));
 
-    let cpu23 = &stat.cpus.expect("Failed to read cpus")[23];
-    assert_eq!(cpu23.user_usec, Some(59379430000));
+    let cpu23_from_vec = &stat.cpus.expect("Failed to read cpus")[22];
+    assert_eq!(cpu23_from_vec.user_usec, Some(59379430000));
+
+    let cpu23_from_map = &stat.cpus_map.expect("Failed to read cpus_map")[&23];
+    assert_eq!(cpu23_from_map.user_usec, Some(59379430000));
 
     assert_eq!(stat.total_interrupt_count, Some(29638874355));
     assert_eq!(stat.context_switches, Some(48203489122));
diff --git a/below/procfs/src/types.rs b/below/procfs/src/types.rs
index 665b4c19..ae97e267 100644
--- a/below/procfs/src/types.rs
+++ b/below/procfs/src/types.rs
@@ -35,7 +35,9 @@ pub struct CpuStat {
 #[derive(Default, Clone, PartialEq, Debug, Serialize, Deserialize)]
 pub struct Stat {
     pub total_cpu: Option<CpuStat>,
+    // TODO: deprecate in favor of cpus_map
     pub cpus: Option<Vec<CpuStat>>,
+    pub cpus_map: Option<BTreeMap<u32, CpuStat>>,
     pub total_interrupt_count: Option<u64>,
     pub context_switches: Option<u64>,
     pub boot_time_epoch_secs: Option<u64>,