add a comment about page size vs bpf ring buffer sizing
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 <maze@google.com>
Change-Id: Ibbce6a72e5e25bf18bb89bca2f00d332ef824f73
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 @@
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 @@
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;
