SCX eBPF macro bpf_obj_drop

v6.12

The bpf_obj_drop macro wraps bpf_obj_drop_impl to provide a more ergonomic interface.

Definition

#define bpf_obj_drop(kptr) bpf_obj_drop_impl(kptr, NULL)

Usage

The bpf_obj_drop_impl kfunc has a quirk where the second argument is always NULL, this wrapper abstracts that quirk away.

Example

/* SPDX-License-Identifier: GPL-2.0 */
/* Copyright (c) 2022 Tejun Heo <tj@kernel.org> */

int BPF_STRUCT_OPS_SLEEPABLE(fcg_cgroup_init, struct cgroup *cgrp,
                 struct scx_cgroup_init_args *args)
{
    struct fcg_cgrp_ctx *cgc;
    struct cgv_node *cgv_node;
    struct cgv_node_stash empty_stash = {}, *stash;
    u64 cgid = cgrp->kn->id;
    int ret;

    /*
     * Technically incorrect as cgroup ID is full 64bit while dsq ID is
     * 63bit. Should not be a problem in practice and easy to spot in the
     * unlikely case that it breaks.
     */
    ret = scx_bpf_create_dsq(cgid, -1);
    if (ret)
        return ret;

    cgc = bpf_cgrp_storage_get(&cgrp_ctx, cgrp, 0,
                   BPF_LOCAL_STORAGE_GET_F_CREATE);
    if (!cgc) {
        ret = -ENOMEM;
        goto err_destroy_dsq;
    }

    cgc->weight = args->weight;
    cgc->hweight = FCG_HWEIGHT_ONE;

    ret = bpf_map_update_elem(&cgv_node_stash, &cgid, &empty_stash,
                  BPF_NOEXIST);
    if (ret) {
        if (ret != -ENOMEM)
            scx_bpf_error("unexpected stash creation error (%d)",
                      ret);
        goto err_destroy_dsq;
    }

    stash = bpf_map_lookup_elem(&cgv_node_stash, &cgid);
    if (!stash) {
        scx_bpf_error("unexpected cgv_node stash lookup failure");
        ret = -ENOENT;
        goto err_destroy_dsq;
    }

    cgv_node = bpf_obj_new(struct cgv_node);
    if (!cgv_node) {
        ret = -ENOMEM;
        goto err_del_cgv_node;
    }

    cgv_node->cgid = cgid;
    cgv_node->cvtime = cvtime_now;

    cgv_node = bpf_kptr_xchg(&stash->node, cgv_node);
    if (cgv_node) {
        scx_bpf_error("unexpected !NULL cgv_node stash");
        ret = -EBUSY;
        goto err_drop;
    }

    return 0;

err_drop:
    bpf_obj_drop(cgv_node);
err_del_cgv_node:
    bpf_map_delete_elem(&cgv_node_stash, &cgid);
err_destroy_dsq:
    scx_bpf_destroy_dsq(cgid);
    return ret;
}