minix/servers/procfs/buf.c
2010-09-14 21:25:25 +00:00

128 lines
2.9 KiB
C

/* ProcFS - buf.c - by Alen Stojanov and David van Moolenbroek */
#include "inc.h"
#include <stdarg.h>
#define BUF_SIZE 4096
PRIVATE char buf[BUF_SIZE + 1];
PRIVATE size_t off, left, used;
PRIVATE off_t skip;
/*===========================================================================*
* buf_init *
*===========================================================================*/
PUBLIC void buf_init(off_t start, size_t len)
{
/* Initialize the buffer for fresh use. The first 'start' bytes of the
* produced output are to be skipped. After that, up to a total of
* 'len' bytes are requested.
*/
skip = start;
left = MIN(len, BUF_SIZE);
off = 0;
used = 0;
}
/*===========================================================================*
* buf_printf *
*===========================================================================*/
PUBLIC void buf_printf(char *fmt, ...)
{
/* Add formatted text to the end of the buffer.
*/
va_list args;
ssize_t len, max;
if (left == 0)
return;
/* There is no way to estimate how much space the result will take, so
* we need to produce the string even when skipping part of the start.
* If part of the result is to be skipped, do not memcpy; instead, save
* the offset of where the result starts within the buffer.
*
* The null terminating character is not part of the result, so room
* must be given for it to be stored after completely filling up the
* requested part of the buffer.
*/
max = MIN(skip + left, BUF_SIZE);
va_start(args, fmt);
len = vsnprintf(&buf[off + used], max + 1, fmt, args);
va_end(args);
if (skip > 0) {
assert(off == 0);
assert(used == 0);
if (skip >= len) {
skip -= len;
return;
}
off = skip;
if (left > BUF_SIZE - off)
left = BUF_SIZE - off;
len -= off;
skip = 0;
}
assert(skip == 0);
assert(len >= 0);
assert((long) left >= 0);
if (len > (ssize_t) left)
len = left;
used += len;
left -= len;
}
/*===========================================================================*
* buf_append *
*===========================================================================*/
PUBLIC void buf_append(char *data, size_t len)
{
/* Add arbitrary data to the end of the buffer.
*/
if (left == 0)
return;
if (skip > 0) {
if (skip >= (ssize_t) len) {
skip -= len;
return;
}
data += skip;
len -= skip;
skip = 0;
}
if (len > left)
len = left;
memcpy(&buf[off + used], data, len);
used += len;
left -= len;
}
/*===========================================================================*
* buf_get *
*===========================================================================*/
PUBLIC size_t buf_get(char **ptr)
{
/* Return the buffer's starting address and the length of the used
* part, not counting the trailing null character for the latter.
*/
*ptr = &buf[off];
return used;
}