linux-kernel - Re: [PATCH] dcache: Define DNAME_INLINE

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Message-ID: <CAADnVQJW+qyq9wPD6RdoaZ8nLYX8N2+4Bhxyd19h6pdqNRMc3A@mail.gmail.com>
Date: Tue, 20 May 2025 10:04:49 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	loongarch@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dcache: Define DNAME_INLINE_LEN as a number directly

On Tue, May 20, 2025 at 1:23 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Tue, May 20, 2025 at 02:47:07PM +0800, Tiezhu Yang wrote:
> > When executing the bcc script, there exists the following error
> > on LoongArch and x86_64:
>
> NOTABUG.  You can't require array sizes to contain no arithmetics,
> including sizeof().  Well, you can, but don't expect your requests
> to be satisfied.
>
> > How to reproduce:
> >
> > git clone https://github.com/iovisor/bcc.git
> > mkdir bcc/build; cd bcc/build
> > cmake ..
> > make
> > sudo make install
> > sudo /usr/share/bcc/tools/filetop
>
> So fix the script.  Or report it to whoever wrote it, if it's
> not yours.

+1

> I'm sorry, but we are NOT going to accomodate random parsers
> poking inside the kernel-internal headers and failing to
> actually parse the language they are written in.
>
> If you want to exfiltrate a constant, do what e.g. asm-offsets is
> doing.  Take a look at e.g.  arch/loongarch/kernel/asm-offsets.c
> and check what ends up in include/generated/asm-offsets.h - the
> latter is entirely produced out of the former.
>
> The trick is to have inline asm that would spew a recognizable
> line when compiled into assembler, with the value(s) you want
> substituted into it.  See include/linux/kbuild.h for the macros.
>
> Then you pick these lines out of generated your_file.s - no need
> to use python, sed(1) will do just fine.  See filechk_offsets in
> scripts/Makefile.lib for that part.

None of it is necessary.

Tiezhu,

bcc's tools/filetop.py is really old and obsolete.
It's not worth fixing. I'd delete it.
Use bcc's libbpf-tools/filetop instead.