From 53d77df5114329ca04155c4be7c284acede78b6c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= Date: Tue, 20 Jun 2023 19:40:22 +0000 Subject: [PATCH] add a comment about page size vs bpf ring buffer sizing MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit As requested by Patrick on: https://android-review.git.corp.google.com/c/platform/system/bpf/+/2628969 bpfLoader: automatically bump ringbuffer size up to page size Test: N/A, comment only Signed-off-by: Maciej Żenczykowski (cherry picked from https://android-review.googlesource.com/q/commit:28f01bb027e5daf9793ed9a436bf735942cd423e) Merged-In: Ibbce6a72e5e25bf18bb89bca2f00d332ef824f73 Change-Id: Ibbce6a72e5e25bf18bb89bca2f00d332ef824f73 --- libbpf_android/Loader.cpp | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp index 231fe39..83f6a88 100644 --- a/libbpf_android/Loader.cpp +++ b/libbpf_android/Loader.cpp @@ -707,6 +707,9 @@ static bool mapMatchesExpectations(const unique_fd& fd, const string& mapName, if (type == BPF_MAP_TYPE_DEVMAP || type == BPF_MAP_TYPE_DEVMAP_HASH) desired_map_flags |= BPF_F_RDONLY_PROG; + // The .h file enforces that this is a power of two, and page size will + // also always be a power of two, so this logic is actually enough to + // force it to be a multiple of the page size, as required by the kernel. unsigned int desired_max_entries = mapDef.max_entries; if (type == BPF_MAP_TYPE_RINGBUF) { if (desired_max_entries < page_size) desired_max_entries = page_size; @@ -849,6 +852,9 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector& type = BPF_MAP_TYPE_HASH; } + // The .h file enforces that this is a power of two, and page size will + // also always be a power of two, so this logic is actually enough to + // force it to be a multiple of the page size, as required by the kernel. unsigned int max_entries = md[i].max_entries; if (type == BPF_MAP_TYPE_RINGBUF) { if (max_entries < page_size) max_entries = page_size;