RE: [PATCH bpf-next] bpf: add bpf_link_new_file that doesn't install FD

[John Fastabend <john.fastabend@gmail.com>]

Andrii Nakryiko wrote:
> Add bpf_link_new_file() API for cases when we need to ensure anon_inode is
> successfully created before we proceed with expensive BPF program attachment
> procedure, which will require equally (if not more so) expensive and
> potentially failing compensation detachment procedure just because anon_inode
> creation failed. This API allows to simplify code by ensuring first that
> anon_inode is created and after BPF program is attached proceed with
> fd_install() that can't fail.
> 
> After anon_inode file is created, link can't be just kfree()'d anymore,
> because its destruction will be performed by deferred file_operations->release
> call. For this, bpf_link API required specifying two separate operations:
> release() and dealloc(), former performing detachment only, while the latter
> frees memory used by bpf_link itself. dealloc() needs to be specified, because
> struct bpf_link is frequently embedded into link type-specific container
> struct (e.g., struct bpf_raw_tp_link), so bpf_link itself doesn't know how to
> properly free the memory. In case when anon_inode file was successfully
> created, but subsequent BPF attachment failed, bpf_link needs to be marked as
> "defunct", so that file's release() callback will perform only memory
> deallocation, but no detachment.
> 
> Convert raw tracepoint and tracing attachment to new API and eliminate
> detachment from error handling path.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---

LGTM

Acked-by: John Fastabend <john.fastabend@gmail.com>