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

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Message-ID: <20241030014818.GG1350452@ZenIV>
Date: Wed, 30 Oct 2024 01:48:18 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Song Liu <song@...nel.org>
Cc: bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	andrii@...nel.org, eddyz87@...il.com, ast@...nel.org,
	daniel@...earbox.net, martin.lau@...ux.dev, brauner@...nel.org,
	jack@...e.cz, kpsingh@...nel.org, mattbobrowski@...gle.com,
	amir73il@...il.com, repnop@...gle.com, jlayton@...nel.org,
	josef@...icpanda.com
Subject: Re: [RFC bpf-next fanotify 2/5] samples/fanotify: Add a sample
 fanotify fastpath handler

On Wed, Oct 30, 2024 at 12:11:55AM +0000, Al Viro 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"???
> 
> 	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...

	After some coproarchaeology: it's probably even worse than java - in
javashit indexOf() predates startsWith() by quite a few years; java itself
had both methods from the very beginning.  So that's probably where it had
been cargo-culted from...

	The thing is, performance requirements of some garbage script from
a javascript-infested webshite are somewhat different from what you want
to see anywhere near the kernel-side filesystem event handling...