NAME¶stenotype - dump raw packets to disk
stenotype [-qv?] [--aiops=NUM] [--blocks=NUM] [--count=NUM] [--dir=STRING] [--fanout_id=NUM] [--fanout_type=NUM] [--fileage_sec=NUM] [--filesize_mb=NUM] [--filter=STRING] [--gid=NUM] [--iface=STRING] [--index_nicelevel=NUM] [--no_index] [--no_watchdogs] [--preallocate_file_mb=NUM] [--seccomp=STRING] [--threads=NUM] [--uid=NUM] [--help] [--usage]
DESCRIPTION¶Stenotype is a mechanism for quickly dumping raw packets to disk. It aims to have a simple interface (no file rotation: that's left as an exercise for the reader) while being very powerful.
stenotype uses a NIC->disk pipeline specifically designed to provide as fast an output to disk as possible while just using the kernel's built-in mechanisms.
- NIC -> RAM: stenotype uses MMAP'd AF_PACKET with 1MB blocks and a high timeout to offload writing packets and deciding their layout to the kernel. The kernel packs all the packets it can into 1MB, then lets the userspace process know there's a block available in the MMAP'd ring buffer. Nicely, it guarantees no overruns (packets crossing the 1MB boundary) and good alignment to memory pages.
- RAM -> Disk: Since the kernel already gave us a single 1MB block of packets that's nicely aligned, we can O_DIRECT write it straight to disk. This avoids any additional copying or kernel buffering. To keep sequential reads going strong, we do all disk IO asynchronously via io_submit (which works specifically for O_DIRECT files... joy!). Since the data is being written to disk asynchronously, we use the time it's writing to disk to do our own in-memory processing and indexing.
There are N (flag-specified) async IO operations available... once we've used up all N, we block on a used one finishing, then reuse it. The whole pipeline consists of:
- kernel gives userspace a 1MB block of packets
- userspace iterates over packets in block, updates any indexes
- userspace starts async IO operation to write block to disk
- after N async IO operations are submitted, we synchronously wait for the least recent one to finish.
- when an async IO operation finishes, we release the 1MB block back to the kernel to write more packets.
- Max number of async IO operations
- Total number of blocks to use, each is 1MB
- Total number of packets to read, -1 to read forever
- Directory to store packet files in
- If fanning out across processes, set this
- TPACKET_V3 fanout type to fanout packets
- Files older than this many secs are rotated
- Max file size in MB before file is rotated
- BPF compiled filter used to filter which packets will be captured. This has to be a compiled BPF in hexadecimal, which can be obtained from a human readable filter expression using the provided compile_bpf.sh script.
- Drop privileges to this group
- Interface to read packets from
- Nice level of indexing threads
- Do not compute or write indexes
- Don't start any watchdogs
- When creating new files, preallocate to this many MB
- Quiet logging. Each -q counteracts one -v
- Seccomp style, one of 'none', 'trace', 'kill'.
- Number of parallel threads to read packets with
- Drop privileges to this user
- Verbose logging, may be given multiple times
- -?, --help
- Give this help list
- Give a short usage message
|11 September 2020||stenographer 1.0.1|