cdb_seek.c

linux下qmail的源码 本人加了一些注释

#include <sys/types.h>
#include <errno.h>
extern int errno;
#include "cdb.h"

#ifndef SEEK_SET
#define SEEK_SET 0
#endif

int cdb_bread(fd,buf,len)
int fd;
char *buf;
int len;
{
  int r;
  while (len > 0) {
    do
      r = read(fd,buf,len);
    while ((r == -1) && (errno == EINTR));
    if (r == -1) return -1;
    if (r == 0) { errno = EIO; return -1; }
    buf += r;
    len -= r;
  }
  return 0;
}

static int match(fd,key,len)
int fd;
char *key;
unsigned int len;
{
  char buf[32];
  int n;
  int i;

  while (len > 0) {
    n = sizeof(buf);
    if (n > len) n = len;
    if (cdb_bread(fd,buf,n) == -1) return -1;
    for (i = 0;i < n;++i) if (buf[i] != key[i]) return 0;
    key += n;
    len -= n;
  }
  return 1;
}

int cdb_seek(fd,key,len,dlen)
int fd;
char *key;
unsigned int len;
uint32 *dlen;
{
  char packbuf[8];
  uint32 pos;
  uint32 h;
  uint32 lenhash;
  uint32 h2;
  uint32 loop;
  uint32 poskd;

  h = cdb_hash(key,len);

  pos = 8 * (h & 255);
  if (lseek(fd,(off_t) pos,SEEK_SET) == -1) return -1;

  if (cdb_bread(fd,packbuf,8) == -1) return -1;

  pos = cdb_unpack(packbuf);
  lenhash = cdb_unpack(packbuf + 4);

  if (!lenhash) return 0;
  h2 = (h >> 8) % lenhash;

  for (loop = 0;loop < lenhash;++loop) {
    if (lseek(fd,(off_t) (pos + 8 * h2),SEEK_SET) == -1) return -1;
    if (cdb_bread(fd,packbuf,8) == -1) return -1;
    poskd = cdb_unpack(packbuf + 4);
    if (!poskd) return 0;
    if (cdb_unpack(packbuf) == h) {
      if (lseek(fd,(off_t) poskd,SEEK_SET) == -1) return -1;
      if (cdb_bread(fd,packbuf,8) == -1) return -1;
      if (cdb_unpack(packbuf) == len)
	switch(match(fd,key,len)) {
	  case -1:
	    return -1;
	  case 1:
	    *dlen = cdb_unpack(packbuf + 4);
	    return 1;
	}
    }
    if (++h2 == lenhash) h2 = 0;
  }
  return 0;
}