writedat.c

UNIX编程高级环境（第二版）的网络套接字部分的程序源码

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

/* Write a data record.  Called by _db_dodelete() (to write
   the record with blanks) and db_store(). */

void
_db_writedat(DB *db, const char *data, off_t offset, int whence)
{
    struct iovec    iov[2];
    static char        newline = '\n';

        /* 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, lock entire file */
        if (writew_lock(db->datfd, 0, SEEK_SET, 0) < 0)
            err_dump("writew_lock error");

    if ( (db->datoff = lseek(db->datfd, offset, whence)) == -1)
        err_dump("lseek error");
    db->datlen = strlen(data) + 1;    /* datlen includes newline */

    iov[0].iov_base = (char *) data;
    iov[0].iov_len  = db->datlen - 1;
    iov[1].iov_base = &newline;
    iov[1].iov_len  = 1;
    if (writev(db->datfd, &iov[0], 2) != db->datlen)
        err_dump("writev error of data record");

    if (whence == SEEK_END)
        if (un_lock(db->datfd, 0, SEEK_SET, 0) < 0)
            err_dump("un_lock error");
}