scbuf.c

#ifndef _SCBUF_C_ /* -*- linux-c -*- */
#define _SCBUF_C_

#include <linux/config.h>

/** @file scbuf.c
 * @addtogroup scbuf Scratch Buffer
 * Scratch Buffer Functions.
 * The scratch buffer is for collecting output before storing in a map,
 * printing, etc. This is a per-cpu static buffer.  It is necessary because 
 * of the limited stack space available in the kernel.
 * @todo Need careful review of these to insure safety.
 * @{
 */

/** Maximum size of buffer, not including terminating NULL */
#define STP_BUF_LEN 8191

/** Scratch buffer for printing, building strings, etc */
static char _stp_scbuf[NR_CPUS][STP_BUF_LEN+1];
static int _stp_scbuf_len[NR_CPUS];

/** Sprint into the scratch buffer.
 * Like printf, except output goes into a global scratch buffer
 * which will contain the null-terminated output.
 * Safe because overflowing the buffer is not allowed.
 * Size is limited by length of scratch buffer, STP_BUF_LEN.
 *
 * @param fmt A printf-style format string followed by a 
 * variable number of args.
 * @sa _stp_scbuf_clear
 */

void _stp_sprint (const char *fmt, ...)
{
        int num;
        va_list args;
        int cpu = smp_processor_id();
        char *buf = _stp_scbuf[cpu] + STP_BUF_LEN - _stp_scbuf_len[cpu];
        va_start(args, fmt);
        num = vscnprintf(buf, _stp_scbuf_len[cpu], fmt, args);
        va_end(args);
        if (num > 0)
                _stp_scbuf_len[cpu] -= num;
}

/** Write a string into the scratch buffer.
 * Copies a string into a global scratch buffer.
 * Safe because overflowing the buffer is not allowed.
 * Size is limited by length of scratch buffer, STP_BUF_LEN.
 * This is more efficient than using _stp_sprint().
 *
 * @param str A string.
 */

void _stp_sprint_str (const char *str)
{
        int cpu = smp_processor_id();
        char *buf = _stp_scbuf[cpu] + STP_BUF_LEN - _stp_scbuf_len[cpu];
        int num = strlen (str);
        if (num > _stp_scbuf_len[cpu])
                num = _stp_scbuf_len[cpu];
        strncpy (buf, str, num);
        _stp_scbuf_len[cpu] -= num;
}

/** Clear the scratch buffer.
 * This function should be called before anything is written to 
 * the scratch buffer.  Output will accumulate in the buffer
 * until this function is called again.  
 * @returns A pointer to the buffer.
 */

char *_stp_scbuf_clear (void)
{
        int cpu = smp_processor_id();
        _stp_scbuf_len[cpu] = STP_BUF_LEN;
        *_stp_scbuf[cpu] = 0;
        return _stp_scbuf[cpu];
}

/** Get the current top of the scratch buffer.
 * This returns the address of the location where
 * data will be written next in the scratch buffer.
 * @returns A pointer
 */

static char *_stp_scbuf_cur (void)
{
        int cpu = smp_processor_id();
        return _stp_scbuf[cpu] + STP_BUF_LEN - _stp_scbuf_len[cpu];
}

/** @} */
#endif /* _SCBUF_C_ */