add duration metric, tolerate missing tracepoints, ship el8 build

- Bubbles, treemap, icicle, and the live flamegraph 'b' cycle now include
  syscall duration (sum) as a third metric alongside events and bytes.
  Statsengine snapshots expose TotalLatencyNs to support this.
- AttachAll takes an optional warn callback. Production passes one so older
  kernels that lack newer tracepoints log a warning and keep going instead
  of aborting startup.
- Dockerfile.el8 + scripts/build-with-docker-el8.sh + mage buildDockerEl8
  produce ior.el8, a static binary built against Rocky Linux 8 glibc for
  RHEL/Rocky/Alma 8 hosts.
- README.md documents installing mage and the new el8 target.

1 files changed, 10 insertions, 0 deletions

diff --git a/Magefile.go b/Magefile.go
index dcde50e..540515c 100644
--- a/Magefile.go
+++ b/Magefile.go
@@ -41,6 +41,7 @@ const (
 	tracepointsGoPath    = "internal/tracepoints/generated_tracepoints.go"
 	typesGoPath          = "internal/types/generated_types.go"
 	dockerBuildScript    = "scripts/build-with-docker.sh"
+	dockerBuildScriptEl8 = "scripts/build-with-docker-el8.sh"
 	typesHeaderPath      = "internal/c/types.h"
 	VMLINUXPath          = "internal/c/vmlinux.h"
 	benchProfilesDir     = "bench-profiles"
@@ -82,6 +83,15 @@ func BuildDocker() error {
 	return sh.RunV("bash", dockerBuildScript)
 }
 
+// BuildDockerEl8 builds the ior binary inside a Rocky Linux 8 Docker container
+// and writes it as ior.el8 in the repo root, alongside the el9 ior binary
+// produced by BuildDocker. Use this when targeting hosts with the older glibc
+// shipped on RHEL/Rocky/Alma 8.  The container image is built on the first
+// run (~15-20 min) and reused thereafter.
+func BuildDockerEl8() error {
+	return sh.RunV("bash", dockerBuildScriptEl8)
+}
+
 // BpfBuild builds the embedded BPF object used by the Go binary.
 func BpfBuild() error {
 	if err := ensureVMLINUX(); err != nil {