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In a bpf fq implementation that is much closer to the kernel fq, it will need to traverse the rbtree: https://lore.kernel.org/bpf/20250418224652.105998-13-martin.lau@linux.dev/ The much simplified logic that uses the bpf_rbtree_{root,left,right} to traverse the rbtree is like: struct fq_flow { struct bpf_rb_node fq_node; struct bpf_rb_node rate_node; struct bpf_refcount refcount; unsigned long sk_long; }; struct fq_flow_root { struct bpf_spin_lock lock; struct bpf_rb_root root __contains(fq_flow, fq_node); }; struct fq_flow *fq_classify(...) { struct bpf_rb_node *tofree[FQ_GC_MAX]; struct fq_flow_root *root; struct fq_flow *gc_f, *f; struct bpf_rb_node *p; int i, fcnt = 0; /* ... */ f = NULL; bpf_spin_lock(&root->lock); p = bpf_rbtree_root(&root->root); while (can_loop) { if (!p) break; gc_f = bpf_rb_entry(p, struct fq_flow, fq_node); if (gc_f->sk_long == sk_long) { f = bpf_refcount_acquire(gc_f); break; } /* To be removed from the rbtree */ if (fcnt < FQ_GC_MAX && fq_gc_candidate(gc_f, jiffies_now)) tofree[fcnt++] = p; if (gc_f->sk_long > sk_long) p = bpf_rbtree_left(&root->root, p); else p = bpf_rbtree_right(&root->root, p); } /* remove from the rbtree */ for (i = 0; i < fcnt; i++) { p = tofree[i]; tofree[i] = bpf_rbtree_remove(&root->root, p); } bpf_spin_unlock(&root->lock); /* bpf_obj_drop the fq_flow(s) that have just been removed * from the rbtree. */ for (i = 0; i < fcnt; i++) { p = tofree[i]; if (p) { gc_f = bpf_rb_entry(p, struct fq_flow, fq_node); bpf_obj_drop(gc_f); } } return f; } The above simplified code needs to traverse the rbtree for two purposes, 1) find the flow with the desired sk_long value 2) while searching for the sk_long, collect flows that are the fq_gc_candidate. They will be removed from the rbtree. This patch adds the bpf_rbtree_{root,left,right} kfunc to enable the rbtree traversal. The returned bpf_rb_node pointer will be a non-owning reference which is the same as the returned pointer of the exisiting bpf_rbtree_first kfunc. Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org> Link: https://lore.kernel.org/r/20250506015857.817950-4-martin.lau@linux.dev Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.