Drop reasons dump (drdump)

Small utility to dump drop reasons from BTF files (by default using the running kernel ones), which can also resolve reasons (raw value to enum variant) and generate bpftrace and stap scripts to dump drop reasons from the skb:kfree_skb tracepoint.

When using the running kernel BTF files, drdump has to run on the target machine or a machine using the same kernel and modules!

Installing

drdump is configured to be build as a static binary when building for x86_64. On Fedora and RHEL, you should install glibc-static before building.

$ git clone https://github.com/retis-org/drdump.git
$ cd drdump
$ cargo build --release
$ ./target/x86_64-unknown-linux-gnu/release/drdump

Pre-built static binaries are available on the release page.

Usage

See the below examples and the drdump --help output.

Examples

Dumping all known drop reasons,

$ drdump
     0 = SKB_NOT_DROPPED_YET
     1 = SKB_CONSUMED
     2 = SKB_DROP_REASON_NOT_SPECIFIED
     3 = SKB_DROP_REASON_NO_SOCKET
     4 = SKB_DROP_REASON_PKT_TOO_SMALL
     5 = SKB_DROP_REASON_TCP_CSUM
...

Resolving a specific raw drop reason,

$ drdump -r 65538
RX_DROP_U_REPLAY
$ drdump -r 65900`
Unknown reason 65900 (sub-system: SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE)

Generating a bpftrace script to monitor drop reasons,

$ drdump -f bpftrace > drop.bt
$ chmod +x drop.bt
$ ./drop.bt
...

Generating a stap script to monitor drop reasons,

$ drdump -f stap > drop.stp
$ stap-prep
$ stap --all-modules drop.stp
...