writeidx.c

用Ｃ语言编的邮件系统（毕业论文）

#include	"mail.h"
#include	<sys/uio.h>		/* struct iovec */

/* Write an index record.
 * _mail_writedat() is called before this function, to set the fields
 * datoff and datlen in the mail structure, which we need to write
 * the index record. */

void
_mail_writeidx(MAIL *mail,struct message *msg,
					 off_t offset, int whence, off_t ptrval)
{
	struct iovec	iov[2];
	char		asciiptrlen[PTR_SZ + IDXLEN_SZ +1];
	int		len;

	if ( (mail->ptrval = ptrval) < 0 || ptrval > PTR_MAX)
		err_quit("invalid ptr: %d", ptrval);

        if(msg!=NULL)
         {
	 sprintf(mail->idxbuf, "%s%c%s%c%d%c%d\n",
		msg->messageid, SEP,hint,SEP, mail->datoff, SEP, mail->datlen);
          
          len=strlen(mail->idxbuf); 
         }
         else len=mail->idxlen;
    
	if ( len < IDXLEN_MIN || len > IDXLEN_MAX)
		err_dump("invalid length");
	sprintf(asciiptrlen, "%*d%*d", PTR_SZ, ptrval, IDXLEN_SZ, len);

		/* If we're appending, we have to lock before doing the lseek()
		   and write() to make the two an atomic operation.  If we're
		   overwriting an existing record, we don't have to lock. */
	if (whence == SEEK_END)		/* we're appending */
		if (writew_lock(mail->idxfd, ((mail->nhash+1)*PTR_SZ)+1,
													SEEK_SET, 0) < 0)
			err_dump("writew_lock error");

		/* Position the index file and record the offset */
	if ( (mail->idxoff = lseek(mail->idxfd, offset, whence)) == -1)
		err_dump("lseek error");

	iov[0].iov_base = asciiptrlen;
	iov[0].iov_len  = PTR_SZ + IDXLEN_SZ;                                   
	iov[1].iov_base = mail->idxbuf;
	iov[1].iov_len  = strlen(mail->idxbuf);
	if (writev(mail->idxfd, &iov[0], 2) != PTR_SZ + IDXLEN_SZ + strlen(mail->idxbuf))
		err_dump("writev error of index record");

	if (whence == SEEK_END)
		if (un_lock(mail->idxfd, ((mail->nhash+1)*PTR_SZ)+1, SEEK_SET, 0) < 0)
			err_dump("un_lock error");
}