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This patch gives an ID to each loaded BTF. The ID is allocated by
the idr like the existing prog-id and map-id.
The bpf_put(map->btf) is moved to __bpf_map_put() so that the
userspace can stop seeing the BTF ID ASAP when the last BTF
refcnt is gone.
It also makes BTF accessible from userspace through the
1. new BPF_BTF_GET_FD_BY_ID command. It is limited to CAP_SYS_ADMIN
which is inline with the BPF_BTF_LOAD cmd and the existing
BPF_[MAP|PROG]_GET_FD_BY_ID cmd.
2. new btf_id (and btf_key_id + btf_value_id) in "struct bpf_map_info"
Once the BTF ID handler is accessible from userspace, freeing a BTF
object has to go through a rcu period. The BPF_BTF_GET_FD_BY_ID cmd
can then be done under a rcu_read_lock() instead of taking
spin_lock.
[Note: A similar rcu usage can be done to the existing
bpf_prog_get_fd_by_id() in a follow up patch]
When processing the BPF_BTF_GET_FD_BY_ID cmd,
refcount_inc_not_zero() is needed because the BTF object
could be already in the rcu dead row . btf_get() is
removed since its usage is currently limited to btf.c
alone. refcount_inc() is used directly instead.
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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 Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
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.