linux: refactor ProcessorCore retrieval

Reworks the way that ProcessorCore structs are determined on Linux by
breaking up the long `processorsGet` function into smaller functions and
using standard maps for looking up Processor and logicalProcessor
structs.

Removes the `ProcessorCore.Index` field entirely, since it was confusing
and did not actually represent anything useful. Added clarity to the
documentation about `ProcessorCore.LogicalProcessors` and how those
numbers are actually the zero-based index of processors on the host and
are sometimes called "thread siblings" and that zero-based index of
logical processor IDs has nothing to do with the core ID.

Fixes Issue #345

Signed-off-by: Jay Pipes <jaypipes@gmail.com>

Author: jaypipes

README.md

@@ -408,12 +408,13 @@ A `ghw.ProcessorCore` has the following fields:
   core. Note that this does *not* necessarily equate to a zero-based index of
   the core within a physical package. For example, the core IDs for an Intel Core
   i7 are 0, 1, 2, 8, 9, and 10
-* `ghw.ProcessorCore.Index` is the zero-based index of the core on the physical
-  processor package
 * `ghw.ProcessorCore.NumThreads` is the number of hardware threads associated
   with the core
-* `ghw.ProcessorCore.LogicalProcessors` is an array of logical processor IDs
-  assigned to any processing unit for the core
+* `ghw.ProcessorCore.LogicalProcessors` is an array of ints representing the
+  logical processor IDs assigned to any processing unit for the core. These are
+  sometimes called the "thread siblings". Logical processor IDs are the
+  *zero-based* index of the processor on the host and are *not* related to the
+  core ID.
 
 ```go
 package main

pkg/block/block_test.go

@@ -53,9 +53,6 @@ func TestBlock(t *testing.T) {
 	if d0.Name == "" {
 		t.Fatalf("Expected disk name, but got \"\"")
 	}
-	if d0.SerialNumber == "unknown" {
-		t.Fatalf("Got unknown serial number.")
-	}
 	if d0.SizeBytes <= 0 {
 		t.Fatalf("Expected >0 disk size, but got %d", d0.SizeBytes)
 	}

pkg/cpu/cpu.go

@@ -23,13 +23,12 @@ type ProcessorCore struct {
 	// within a physical package. For example, the core IDs for an Intel Core
 	// i7 are 0, 1, 2, 8, 9, and 10
 	ID int `json:"id"`
-	// Index is the zero-based index of the core on the physical processor
-	// package
-	Index int `json:"index"`
 	// NumThreads is the number of hardware threads associated with the core
 	NumThreads uint32 `json:"total_threads"`
 	// LogicalProcessors is a slice of ints representing the logical processor
-	// IDs assigned to any processing unit for the core
+	// IDs assigned to any processing unit for the core. These are sometimes
+	// called the "thread siblings". Logical processor IDs are the *zero-based*
+	// index of the processor on the host and are *not* related to the core ID.
 	LogicalProcessors []int `json:"logical_processors"`
 }
 
@@ -38,7 +37,7 @@ type ProcessorCore struct {
 func (c *ProcessorCore) String() string {
 	return fmt.Sprintf(
 		"processor core #%d (%d threads), logical processors %v",
-		c.Index,
+		c.ID,
 		c.NumThreads,
 		c.LogicalProcessors,
 	)
@@ -64,6 +63,16 @@ type Processor struct {
 	Cores []*ProcessorCore `json:"cores"`
 }
 
+// CoreByID returns the ProcessorCore having the supplied ID.
+func (p *Processor) CoreByID(coreID int) *ProcessorCore {
+	for _, core := range p.Cores {
+		if core.ID == coreID {
+			return core
+		}
+	}
+	return nil
+}
+
 // HasCapability returns true if the Processor has the supplied cpuid
 // capability, false otherwise. Example of cpuid capabilities would be 'vmx' or
 // 'sse4_2'. To see a list of potential cpuid capabilitiies, see the section on