lftruncate.c

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/* lftruncate.c - lftruncate */

#include <xinu.h>

/*------------------------------------------------------------------------
 * lftruncate  -  Truncate a file by freeing its index and data blocks
 *          (assumes directory mutex held)
 *------------------------------------------------------------------------
 */
status  lftruncate (
      struct lflcblk *lfptr     /* Ptr to file's cntl blk entry */
    )
{
    struct  ldentry *ldptr;     /* Pointer to file's dir. entry */
    struct  lfiblk  iblock;     /* Buffer for one index block   */
    ibid32  ifree;          /* Start of index blk free list */
    ibid32  firstib;        /* First index blk of the file  */
    ibid32  nextib;         /* Walks down list of the   */
                    /*   file's index blocks    */
    dbid32  nextdb;         /* Next data block to free  */
    int32   i;          /* Moves through data blocks in */
                    /*   a given index block    */

    ldptr = lfptr->lfdirptr;    /* Get pointer to dir. entry    */
    if (ldptr->ld_size == 0) {  /* File is already empty */
        return OK;
    }

    /* Clean up the open local file first */

    if ( (lfptr->lfibdirty) || (lfptr->lfdbdirty) ) {
        lfflush(lfptr);
    }
    lfptr->lfpos = 0;
    lfptr->lfinum = LF_INULL;
    lfptr->lfdnum = LF_DNULL;
    lfptr->lfbyte = &lfptr->lfdblock[LF_BLKSIZ];

    /* Obtain ID of first index block on free list */

    ifree = Lf_data.lf_dir.lfd_ifree;

    /* Record file's first i-block and clear directory entry */

    firstib = ldptr->ld_ilist;
    ldptr->ld_ilist = LF_INULL;
    ldptr->ld_size = 0;
    Lf_data.lf_dirdirty = TRUE;

    /* Walk along index block list, disposing of each data block    */
    /*   and clearing the corresponding pointer.  A note on loop    */
    /*   termination: last pointer is set to ifree below.       */

    for (nextib=firstib; nextib!=ifree; nextib=iblock.ib_next) {

        /* Obtain a copy of current index block from disk   */

        lfibget(Lf_data.lf_dskdev, nextib, &iblock);

        /* Free each data block in the index block      */

        for (i=0; i<LF_IBLEN; i++) {    /* For each d-block */

            /* Free the data block */

            nextdb = iblock.ib_dba[i];
            if (nextdb != LF_DNULL) {
                lfdbfree(Lf_data.lf_dskdev, nextdb);
            }

            /* Clear entry in i-block for this d-block  */

                iblock.ib_dba[i] = LF_DNULL;
        }

        /* Clear offset (just to make debugging easier)     */

        iblock.ib_offset = 0;

        /* For the last index block on the list, make it point  */
        /*  to the current free list            */

        if (iblock.ib_next == LF_INULL) {
            iblock.ib_next = ifree;
        }

        /* Write cleared i-block back to disk */

        lfibput(Lf_data.lf_dskdev, nextib, &iblock);
    }

    /* Last index block on the file list now points to first node   */
    /*   on the current free list.  Once we make the free list  */
    /*   point to the first index block on the file list, the   */
    /*   entire set of index blocks will be on the free list    */

    Lf_data.lf_dir.lfd_ifree = firstib;

    /* Indicate that directory has changed and return */

    Lf_data.lf_dirdirty = TRUE;
    
    return OK;
}