Re: [RFC][PATCH 03/12 v3] tracing: Create seq_buf layer in trace_seq

Steven Rostedt
2014-11-05T20:00:12Z

On Wed, 5 Nov 2014 13:41:47 -0500
Steven Rostedt <rostedt@goodmis.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;
> > > +}
> > > +
> >