linux-kernel - Re: [PATCH] btf: Use BIN_ATTR_SIMPLE

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Message-ID: <CAEf4BzbNs=MVNDztRW_76f8aQkm44ykiibqGa2REThWM4dVa_g@mail.gmail.com>
Date: Tue, 26 Nov 2024 13:37:26 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btf: Use BIN_ATTR_SIMPLE_RO() to define vmlinux attribute

On Fri, Nov 22, 2024 at 4:57 AM Thomas Weißschuh <linux@...ssschuh.net> wrote:
>
> The usage of the macro allows to remove the custom handler function,
> saving some memory. Additionally the code is easier to read.
>
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
> Something similar can be done to btf_module_read() in kernel/bpf/btf.c.
> But doing it here and now would lead to some conflicts with some other
> sysfs refactorings I'm doing. It will be part of a future series.
> ---
>  kernel/bpf/sysfs_btf.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)
>

Nice, let's simplify. But why change the name to generic "vmlinux" if
it's actually btf_vmlinux? Can we keep the original btf-specific name?

pw-bot: cr

> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index fedb54c94cdb830a4890d33677dcc5a6e236c13f..a24381f933d0b80b11116d05463c35e9fa66acb1 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -12,34 +12,23 @@
>  extern char __start_BTF[];
>  extern char __stop_BTF[];
>
> -static ssize_t
> -btf_vmlinux_read(struct file *file, struct kobject *kobj,
> -                struct bin_attribute *bin_attr,
> -                char *buf, loff_t off, size_t len)
> -{
> -       memcpy(buf, __start_BTF + off, len);
> -       return len;
> -}
> -
> -static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> -       .attr = { .name = "vmlinux", .mode = 0444, },
> -       .read = btf_vmlinux_read,
> -};
> +static __ro_after_init BIN_ATTR_SIMPLE_RO(vmlinux);
>
>  struct kobject *btf_kobj;
>
>  static int __init btf_vmlinux_init(void)
>  {
> -       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> +       bin_attr_vmlinux.private = __start_BTF;
> +       bin_attr_vmlinux.size = __stop_BTF - __start_BTF;
>
> -       if (bin_attr_btf_vmlinux.size == 0)
> +       if (bin_attr_vmlinux.size == 0)
>                 return 0;
>
>         btf_kobj = kobject_create_and_add("btf", kernel_kobj);
>         if (!btf_kobj)
>                 return -ENOMEM;
>
> -       return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
> +       return sysfs_create_bin_file(btf_kobj, &bin_attr_vmlinux);
>  }
>
>  subsys_initcall(btf_vmlinux_init);
>
> ---
> base-commit: 28eb75e178d389d325f1666e422bc13bbbb9804c
> change-id: 20241122-sysfs-const-bin_attr-bpf-737286bb9f27
>
> Best regards,
> --
> Thomas Weißschuh <linux@...ssschuh.net>
>