linux-kernel - RE: [PATCH] seq_file: Optimize seq

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Date: Tue, 16 Apr 2024 20:56:51 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Al Viro' <viro@...iv.linux.org.uk>, Christophe JAILLET
	<christophe.jaillet@...adoo.fr>
CC: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH] seq_file: Optimize seq_puts()

From: Al Viro
> Sent: 15 April 2024 22:01
..
> No need to make it a macro, actually.  And I would suggest going
> a bit further:
> 
> static inline void seq_puts(struct seq_file *m, const char *s)

That probably needs to be 'always_inline'.

> {
>	if (!__builtin_constant_p(*s))
> 		__seq_puts(m, s);
> 	else if (s[0] && !s[1])
> 		seq_putc(m, s[0]);
> 	else
> 		seq_write(m, s, __builtin_strlen(s));
> }

You missed seq_puts(m, "");

I did wonder about checking sizeof(s) <= 2 in the #define version.
That would pick up the cases where a separator is changed/added
in a loop.

Could you do:
	size_t len = __builtin_strlen(s);
	if (!__builtin_constant_p(len))
		__seq_puts(m, s);
	else switch (len){
	case 0: break;
	case 1: seq_putc(m, s[0]);
	default: seq_write(m, s, len);
	}

	David

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