> On Oct 28, 2020, at 5:58 PM, Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> From: Andrii Nakryiko <andriin@xxxxxx>
>
> Revamp BTF dedup's string deduplication to match the approach of writable BTF
> string management. This allows to transfer deduplicated strings index back to
> BTF object after deduplication without expensive extra memory copying and hash
> map re-construction. It also simplifies the code and speeds it up, because
> hashmap-based string deduplication is faster than sort + unique approach.
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
LGTM, with a couple nitpick below:
Acked-by: Song Liu <songliubraving@xxxxxx>
> ---
> tools/lib/bpf/btf.c | 265 +++++++++++++++++---------------------------
> 1 file changed, 99 insertions(+), 166 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 89fecfe5cb2b..db9331fea672 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -90,6 +90,14 @@ struct btf {
> struct hashmap *strs_hash;
> /* whether strings are already deduplicated */
> bool strs_deduped;
> + /* extra indirection layer to make strings hashmap work with stable
> + * string offsets and ability to transparently choose between
> + * btf->strs_data or btf_dedup->strs_data as a source of strings.
> + * This is used for BTF strings dedup to transfer deduplicated strings
> + * data back to struct btf without re-building strings index.
> + */
> + void **strs_data_ptr;
> +
> /* BTF object FD, if loaded into kernel */
> int fd;
>
> @@ -1363,17 +1371,19 @@ int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
>
> static size_t strs_hash_fn(const void *key, void *ctx)
> {
> - struct btf *btf = ctx;
> - const char *str = btf->strs_data + (long)key;
> + const char ***strs_data_ptr = ctx;
> + const char *strs = **strs_data_ptr;
> + const char *str = strs + (long)key;
Can we keep using btf as the ctx here? "char ***" hurts my eyes...
[...]
> - d->btf->hdr->str_len = end - start;
> + /* replace BTF string data and hash with deduped ones */
> + free(d->btf->strs_data);
> + hashmap__free(d->btf->strs_hash);
> + d->btf->strs_data = d->strs_data;
> + d->btf->strs_data_cap = d->strs_cap;
> + d->btf->hdr->str_len = d->strs_len;
> + d->btf->strs_hash = d->strs_hash;
> + /* now point strs_data_ptr back to btf->strs_data */
> + d->btf->strs_data_ptr = &d->btf->strs_data;
> +
> + d->strs_data = d->strs_hash = NULL;
> + d->strs_len = d->strs_cap = 0;
> d->btf->strs_deduped = true;
> + return 0;
> +
> +err_out:
> + free(d->strs_data);
> + hashmap__free(d->strs_hash);
> + d->strs_data = d->strs_hash = NULL;
> + d->strs_len = d->strs_cap = 0;
> +
> + /* restore strings pointer for existing d->btf->strs_hash back */
> + d->btf->strs_data_ptr = &d->strs_data;
We have quite some duplicated code in err_out vs. succeed_out cases.
How about we add a helper function, like
void free_strs_data(struct btf_dedup *d)
{
free(d->strs_data);
hashmap__free(d->strs_hash);
d->strs_data = d->strs_hash = NULL;
d->strs_len = d->strs_cap = 0;
}
?
