Libbpf eBPF macro BPF_SEQ_PRINTF

v0.0.9

Note

This macro was moved from bpf_tracing.h to bpf_helpers.h in v0.5.0

The BPF_SEQ_PRINTF macro is used to make printing to bpf iterator sequence files easier.

Definition

/*
 * BPF_SEQ_PRINTF to wrap bpf_seq_printf to-be-printed values
 * in a structure.
 */
#define BPF_SEQ_PRINTF(seq, fmt, args...)           \
({                              \
    static const char ___fmt[] = fmt;           \
    unsigned long long ___param[___bpf_narg(args)];     \
                                \
    _Pragma("GCC diagnostic push")              \
    _Pragma("GCC diagnostic ignored \"-Wint-conversion\"")  \
    ___bpf_fill(___param, args);                \
    _Pragma("GCC diagnostic pop")               \
                                \
    bpf_seq_printf(seq, ___fmt, sizeof(___fmt),     \
               ___param, sizeof(___param));     \
})

Usage

This macro is a wrapper around the bpf_seq_printf helper. It places the literal format string in a global variable, this is necessary to get the compiler to emit code that will be accepted by the verifier.

Example

SEC("iter/task_file")
int dump_task_file(struct bpf_iter__task_file *ctx)
{
    struct seq_file *seq = ctx->meta->seq;
    struct task_struct *task = ctx->task;
    struct file *file = ctx->file;
    __u32 fd = ctx->fd;

    if (task == NULL || file == NULL)
        return 0;

    if (ctx->meta->seq_num == 0) {
        count = 0;
        BPF_SEQ_PRINTF(seq, "    tgid      gid       fd      file\n");
    }

    if (tgid == task->tgid && task->tgid != task->pid)
        count++;

    if (last_tgid != task->tgid) {
        last_tgid = task->tgid;
        unique_tgid_count++;
    }

    BPF_SEQ_PRINTF(seq, "%8d %8d %8d %lx\n", task->tgid, task->pid, fd,
            (long)file->f_op);
    return 0;
}