open.c

unix环境高级编程的源代码

#include    "db.h"

/* Open or create a database.  Same arguments as open(). */

DB *
db_open(const char *pathname, int oflag, int mode)
{
    DB            *db;
    int            i, len;
    char        asciiptr[PTR_SZ + 1],
                hash[(NHASH_DEF + 1) * PTR_SZ + 2];
                    /* +2 for newline and null */
    struct stat    statbuff;

        /* Allocate a DB structure, and the buffers it needs */
    len = strlen(pathname);
    if ( (db = _db_alloc(len)) == NULL)
        err_dump("_db_alloc error for DB");

    db->oflag = oflag;        /* save a copy of the open flags */

        /* Open index file */
    strcpy(db->name, pathname);
    strcat(db->name, ".idx");
    if ( (db->idxfd = open(db->name, oflag, mode)) < 0) {
        _db_free(db);
        return(NULL);
    }
        /* Open data file */
    strcpy(db->name + len, ".dat");
    if ( (db->datfd = open(db->name, oflag, mode)) < 0) {
        _db_free(db);
        return(NULL);
    }

        /* If the database was created, we have to initialize it */
    if ((oflag & (O_CREAT | O_TRUNC)) == (O_CREAT | O_TRUNC)) {
            /* Write lock the entire file so that we can stat
               the file, check its size, and initialize it,
               as an atomic operation. */
        if (writew_lock(db->idxfd, 0, SEEK_SET, 0) < 0)
            err_dump("writew_lock error");

        if (fstat(db->idxfd, &statbuff) < 0)
            err_sys("fstat error");
        if (statbuff.st_size == 0) {
                /* We have to build a list of (NHASH_DEF + 1) chain
                   ptrs with a value of 0.  The +1 is for the free
                   list pointer that precedes the hash table. */
            sprintf(asciiptr, "%*d", PTR_SZ, 0);
            hash[0] = 0;
            for (i = 0; i < (NHASH_DEF + 1); i++)
                strcat(hash, asciiptr);
            strcat(hash, "\n");

            i = strlen(hash);
            if (write(db->idxfd, hash, i) != i)
                err_dump("write error initializing index file");
        }
        if (un_lock(db->idxfd, 0, SEEK_SET, 0) < 0)
            err_dump("un_lock error");
    }
    db->nhash   = NHASH_DEF;/* hash table size */
    db->hashoff = HASH_OFF;    /* offset in index file of hash table */
                            /* free list ptr always at FREE_OFF */
    db_rewind(db);

    return(db);
}