linux-kernel - Re: [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in trace

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Message-ID: <20141105150007.1c543b9e@gandalf.local.home>
Date:	Wed, 5 Nov 2014 15:00:07 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in
 trace_seq

On Wed, 5 Nov 2014 13:41:47 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> > 
> > > + */
> > > +int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
> > > +		    int nmaskbits)
> > > +{
> > > +	unsigned int len = SEQ_BUF_LEFT(s);
> > >
> > > +	int ret;
> > > +
> > > +	WARN_ON(s->size == 0);
> > > +
> > > +	if (s->len < s->size) {
> > > +		ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
> > 
> > It writes to the beginning of the buffer. It should be
> > 
> > 		ret = bitmap_scnprintf(s->buffer + s->len, len,
> > 				       maskp, nmaskbits);
> >
> 
> Yep thanks. Luckily its only user didn't care.
> 
> Will fix.
>  
> > 
> > > +		if (s->len + ret < s->size) {
> > 
> > This will always happen because bitmap_scnprintf() is limited by SEQ_BUF_LEFT(s)
> > and it currently returns the remaining size - len - 1.
> 
> Hmm, that's correct, as bitmap_scnprintf() returns the amount written
> instead of the amount that it would write like snprintf() would.
> 
> 
> > 
> > You might want to use "s->size - s->len" instead of SEQ_BUF_LEFT(s).
> 
> That wont help when we make overflow len > size.
> 
> Probably should see if ret == the amount of bits required for the
> bitmask.

Here's the new version:

int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
		    int nmaskbits)
{
	unsigned int len = seq_buf_buffer_left(s);
	int size;
	int ret;

	WARN_ON(s->size == 0);

	if (s->len < s->size) {
		/*
		 * Calculate to see if we have enough room to fit
		 * @nmaskbits as a string
		 */
		size = (nmaskbits + 3) / 4;
		/* Add the commas that are used for groups of 8 hex digits */
		size += size / 8;
		if (len >= size) {
			ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
			WARN_ON_ONCE(s->len + ret >= s->size);
			s->len += ret;
			return 0;
		}
	}
	seq_buf_set_overflow(s);
	return -1;
}


> 
> > 
> > 
> > > +			s->len += ret;
> > > +			return 0;
> > > +		}
> > > +	}
> > > +	seq_buf_set_overflow(s);
> > > +	return -1;
> > > +}



> > > +/**
> > > + * seq_buf_putmem_hex - write raw memory into the buffer in ASCII hex
> > > + * @s: seq_buf descriptor
> > > + * @mem: The raw memory to write its hex ASCII representation of
> > > + * @len: The length of the raw memory to copy (in bytes)
> > > + *
> > > + * This is similar to seq_buf_putmem() except instead of just copying the
> > > + * raw memory into the buffer it writes its ASCII representation of it
> > > + * in hex characters.
> > > + *
> > > + * Returns zero on success, -1 on overflow
> > > + */
> > > +int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
> > > +		       unsigned int len)
> > > +{
> > > +	unsigned char hex[HEX_CHARS];
> > > +	const unsigned char *data = mem;
> > > +	unsigned int start_len;
> > > +	int i, j;
> > > +
> > > +	WARN_ON(s->size == 0);
> > > +
> > > +	while (len) {
> > > +		start_len = min(len, HEX_CHARS - 1);
> > > +#ifdef __BIG_ENDIAN
> > > +		for (i = 0, j = 0; i < start_len; i++) {
> > > +#else
> > > +		for (i = start_len-1, j = 0; i >= 0; i--) {
> > > +#endif
> > > +			hex[j++] = hex_asc_hi(data[i]);
> > > +			hex[j++] = hex_asc_lo(data[i]);
> > > +		}
> > > +		if (WARN_ON_ONCE(j == 0 || j/2 > len))
> > > +			break;
> > > +
> > > +		/* j increments twice per loop */
> > > +		len -= j / 2;
> > > +		hex[j++] = ' ';
> > > +
> > > +		seq_buf_putmem(s, hex, j);
> > > +		if (seq_buf_has_overflowed(s))
> > 
> > We might want to use the seq_buf_putmem() return value here.
> 
> We could do that.

Actually, no we can't. As I stated before, the return values of most
of the seq_*() functions (for seq_file and seq_buf) will be turning
into void functions.

I'm avoiding checking return values here.

-- Steve

> 
> > 
> > > +			return -1;
> > > +	}
> > > +	return 0;
> > > +}
> > > +
> > 

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