What is eBPF bpf_iter and why does it replace legacy /proc file system scraping?

Traditionally, system monitoring tools (such as ps, top, lsof, and netstat) inspect kernel state by traversing pseudo-filesystems like /proc and /sys. For each process and thread, user space opens directory entries (/proc/[pid]/status, /proc/[pid]/fd), triggering thousands of system calls (open, read, close), dcache lock allocations, and tasklist_lock read locks. When inspecting high-density node environments with 50,000+ containers or threads, /proc scraping causes severe lock contention and CPU thrashing. eBPF bpf_iter (introduced in Linux kernel 5.8) allows developers to write an in-kernel iterator program (SEC("iter/task")) that streams kernel data structures directly into user space buffers via a single file descriptor and the seq_file interface with zero dcache churn and minimal lock holding times.

What are the primary eBPF iterator targets supported by the Linux kernel?

The Linux kernel provides several specialized iterator types: 1) bpf_iter_task: Traverses the global task_struct list or threads of a specific thread group; 2) bpf_iter_task_file: Iterates over every open struct file descriptor (files_struct) of every process, replacing lsof; 3) bpf_iter_task_vma: Iterates through memory mapping regions (vm_area_struct) without acquiring mm->mmap_lock for prolonged periods, replacing /proc/[pid]/maps; 4) bpf_iter_tcp & bpf_iter_udp: Iterates directly through socket hash tables (inet_hashinfo) to inspect TCP/UDP connection state without locking entire socket buckets.

How does the seq_file architecture work with bpf_seq_read and bpf_seq_printf?

Under the hood, creating an iterator creates an anonymous file descriptor linked to an in-kernel struct seq_file. When userspace invokes read(iter_fd, buf, size), the kernel enters bpf_seq_read(). In a loop, the kernel advances through internal kernel objects, invokes the user's eBPF program with a context pointer (e.g., struct bpf_iter__task *ctx), and provides helpers like bpf_seq_printf() or bpf_seq_write() to serialize data directly into the pre-allocated seq_file buffer. Once the buffer fills or iteration ends, control returns to user space in a single batch read.

How does bpf_iter handle concurrent process creation and termination during traversal?

eBPF iterators leverage RCU (Read-Copy Update) and task references (get_task_struct) to guarantee memory safety. When iterating tasks, the iterator holds an RCU read lock and safe list cursors. If a process terminates while the iterator is paused between seq_file read batches, the kernel's struct task_struct remains safely pinned in memory until the iterator advances, preventing use-after-free crashes. While transient processes created after iteration starts may or may not be observed, no memory corruption or deadlocks can occur.

Linux eBPF bpf_iter & Kernel Task Iterators Studio | In-Kernel Streaming Observability

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Linux 5.8+ Kernel ABI eBPF • bpf_iter Zero /proc Thrashing

Linux eBPF bpf_iter & Kernel Task Iterators Studio

Simulate high-efficiency kernel state streaming using eBPF iterators. Compare in-kernel sequence batching against legacy /proc filesystem walking, evaluate lock contention and dentry allocations across high-density workloads, and export production C eBPF and Go Cilium programs.

1. Target Iterator & Workload Scale

Iterator Target Type: System Workload Scale (Total Entities):

25,000

In-Kernel Filter Predicate:

2. Kernel seq_file & Buffer Tuning

Userspace Read Buffer Size (PAGE_SIZE multiples): Output Serialization Method: Locking Paradigm in Target Subsystem:

RCU read-lock + task_struct reference pinning. Zero global tasklist_lock acquisition.

Performance Comparison: eBPF bpf_iter vs Legacy /proc Walking

~28.4x Lower Overhead

Total System Calls

2 syscalls

vs 75,000 (/proc)

Dcache / VFS Dentries Allocated

0 dentries

vs 25,000 (/proc)

Execution Latency

1.85 ms

vs 52.4 ms (/proc)

Kernel CPU Core-Time

1.2 ms

vs 38.6 ms (/proc)

Production Implementation Code

Architectural Comparison: /proc Filesystem vs eBPF bpf_iter

Dimension	eBPF bpf_iter (Linux 5.8+)	Legacy /proc Filesystem
System Call Overhead	O(Bytes / BufferSize) — typically 2-10 read() calls	O(Entities × Files) — tens of thousands of open/read/close
VFS & Dcache Churn	Zero dentry allocations; uses anonymous bpf inode	Massive dcache allocations; flushes useful cache lines
Filtering Placement	In-Kernel (Only matching records are formatted and copied)	User Space (100% of files must be opened and parsed)
Lock Contention	Non-blocking RCU read-side critical sections	Heavy tasklist_lock / mm->mmap_lock read lock holding

Linux eBPF bpf_iter & Kernel Task Iterators Studio

1. Target Iterator & Workload Scale

2. Kernel seq_file & Buffer Tuning

Performance Comparison: eBPF bpf_iter vs Legacy /proc Walking

Production Implementation Code

Architectural Comparison: /proc Filesystem vs eBPF bpf_iter

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