lflseek.c

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/* lflseek.c - lflseek */

#include <xinu.h>

/*------------------------------------------------------------------------
 * lflseek  -  Seek to a specified position in a file
 *------------------------------------------------------------------------
 */
devcall lflseek (
      struct dentry *devptr,    /* Entry in device switch table */
      uint32    offset      /* Byte position in the file    */
    )
{
    struct  lflcblk *lfptr;     /* Ptr to open file table entry */

    /* If file is not open, return an error */

    lfptr = &lfltab[devptr->dvminor];
    wait(lfptr->lfmutex);
    if (lfptr->lfstate != LF_USED) {
        signal(lfptr->lfmutex);
        return SYSERR;
    }

    /* Verify offset is within current file size */

    if (offset > lfptr->lfdirptr->ld_size) {
        signal(lfptr->lfmutex);
        return SYSERR;
    }

    /* Record new offset and invalidate byte pointer (i.e., force   */
    /*   the index and data blocks to be replaced if a successive   */
    /*   call is made to read or write)             */

    lfptr->lfpos = offset;
    lfptr->lfbyte = &lfptr->lfdblock[LF_BLKSIZ];

    signal(lfptr->lfmutex);
    return OK;
}