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

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Message-ID: <5307ea3b-6720-4ca9-827e-7338f255908f@t-8ch.de>
Date: Tue, 26 Nov 2024 22:42:15 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
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 2024-11-26 13:37:26-0800, Andrii Nakryiko wrote:
> 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?

The file in sysfs is named "vmlinux", /sys/kernel/btf/vmlinux.
This is what needs to be passed to the macro, it will name both the
variable and the file after it.

One alternative would be to use __BIN_ATTR_SIMPLE_RO() which allows a
custom 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>
> >