feat(disruption): disk full injection.

[Zenithar]

What does this PR do?

• Adds new functionality

Adds a new diskFull disruption kind that genuinely fills a target pod volume using the fallocate(2) syscall, causing real ENOSPC errors on all subsequent write operations. This fills a gap where existing disruptions (DiskPressure = I/O throttling, DiskFailure = eBPF on openat only) don't simulate actual disk exhaustion visible to monitoring and all syscalls.

Features

• Volume fill (v1): Creates a ballast file via fallocate(2) syscall (instant, O(1) on ext4/xfs) to genuinely consume disk space. Falls back to writing zeros on unsupported filesystems.
• eBPF write interception (v2, optional): Launches an eBPF program to intercept write syscalls and return configurable error codes (ENOSPC, EDQUOT, EIO, etc.) with probability-based failure injection.
• Safety: 1Mi minimum free space floor (overridable via unsafeMode.allowDiskFullNoFloor). Pod-level only. Webhook warning for ephemeral-storage eviction risk.
• Pure Go fallocate: Vendored fallocate/ package (adapted from detailyang/go-fallocate, MIT) — no dependency on fallocate or dd binaries in the injector image.

How it differs from existing disruptions

Disruption	Mechanism	ENOSPC on writes?	Visible to df/monitoring?
Disk Pressure	Cgroup blkio throttling	No	No
Disk Failure	eBPF on openat only	Only on file open	No
Disk Full (new)	Real space allocation + optional eBPF	Yes (all syscalls)	Yes

Example

apiVersion: chaos.datadoghq.com/v1beta1
kind: Disruption
metadata:
  name: disk-full-test
spec:
  selector:
    app: my-service
  count: 1
  level: pod
  duration: 10m
  diskFull:
    path: "/data"
    capacity: "95%"
    # Optional: eBPF write interception
    writeSyscall:
      exitCode: ENOSPC
      probability: "50%"

Code Quality Checklist

• The documentation is up to date.
• My code is sufficiently commented and passes continuous integration checks.
• I have signed my commit (see Contributing Docs).

Testing

• I leveraged continuous integration testing
  • by adding new unit tests.
• I manually tested the following steps:
  • locally.
  • as a canary deployment to a cluster.

Test coverage (50 specs)

• Spec validation (39 tests): capacity/remaining mutual exclusivity, boundary values, writeSyscall probability, GenerateArgs, Explain, GetExitCodeInt
• Injector (11 tests): creation, inject with capacity/remaining, dry-run, remaining > available (skip), inject+clean round trip, idempotent cleanup

Files changed (27 files, ~2000 lines)

Component	Files
CRD spec + validation	api/v1beta1/disk_full.go, disruption_types.go, disruption_webhook.go, safemode.go
Injector	injector/disk_full.go (volume fill + eBPF launch)
CLI	cli/injector/disk_full.go, cli/injector/main.go
fallocate package	fallocate/ (4 platform-specific files, adapted from go-fallocate MIT)
eBPF program	ebpf/disk-full-write/ (C kernel program + Go userspace binary)
Safemode	safemode/safemode_disk_full.go, safemode/safemode.go
Types	types/types.go (DisruptionKindDiskFull), ebpf/const-*.go (SysWrite)
Docs	docs/disk_full.md, docs/disruption_catalogue.md
Tests	api/v1beta1/disk_full_test.go, injector/disk_full_test.go

[datadog-prod-us1-4]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 57.09%
• Overall Coverage: 38.98% (+0.49%)

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