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