linux-kernel - Re: [RFC bpf-next fanotify 2/5] samples/fanotify: Add a sample fanotify fastpath handler

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Message-ID: <0D8D4346-722D-4430-B15D-FA1E40073CFE@fb.com>
Date: Wed, 30 Oct 2024 02:07:01 +0000
From: Song Liu <songliubraving@...a.com>
To: Al Viro <viro@...iv.linux.org.uk>
CC: Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Linux-Fsdevel
	<linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel
 Team <kernel-team@...a.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Eduard
 Zingerman <eddyz87@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel
 Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        KP Singh
	<kpsingh@...nel.org>,
        Matt Bobrowski <mattbobrowski@...gle.com>,
        Amir
 Goldstein <amir73il@...il.com>,
        "repnop@...gle.com" <repnop@...gle.com>,
        "jlayton@...nel.org" <jlayton@...nel.org>,
        Josef Bacik <josef@...icpanda.com>
Subject: Re: [RFC bpf-next fanotify 2/5] samples/fanotify: Add a sample
 fanotify fastpath handler



> On Oct 29, 2024, at 5:11 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> 
> On Tue, Oct 29, 2024 at 04:12:41PM -0700, Song Liu wrote:
>> + if (strstr(file_name->name, item->prefix) == (char *)file_name->name)
> 
> Huh?  "Find the first substring (if any) equal to item->prefix and
> then check if that happens to be in the very beginning"???

Replaced it with strcmp locally, assuming strncmp is not necessary.

> 
> And you are placing that into the place where it's most likely to cause
> the maximal braindamage and spread all over the tree.  Wonderful ;-/
> 
> Where does that "idiom" come from, anyway?  Java?  Not the first time
> I see that kind of garbage; typecast is an unusual twist, though...

The strstr() was probably from lack of coffee. The cast is most likely 
from the compiler yelling at sleepy me. 

BTW: Why do we need "const unsigned char *" in qstr instead of 
"const char *"? I do notice git doesn't show the real history of it..

Thanks,
Song