Re: [PATCH] seq_file: Optimize seq_puts()

[Christophe JAILLET]

Le 16/04/2024 à 22:56, David Laight a écrit :
> 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.

git grep seq_puts.*\"[^\\].\" | wc -l
77

What would you do in this case?
2 seq_putc() in order to save a memcpy(..., 2), that's it?

It would also slightly change the behaviour, as only the 1st char could 
be added. Actually, it is all or nothing.

Don't know what is the best.

Any thought?

CJ


> 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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