lflputc.c

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/* lflputc.c - lfputc */

#include <xinu.h>

/*------------------------------------------------------------------------
 * lflputc  -  Write a single byte to an open local file
 *------------------------------------------------------------------------
 */
devcall lflputc (
      struct dentry *devptr,    /* Entry in device switch table */
      char      ch      /* Character (byte) to write    */
    )
{
    struct  lflcblk *lfptr;     /* Ptr to open file table entry */
    struct  ldentry *ldptr;     /* Ptr to file's entry in the   */
                    /*  in-memory directory     */

    /* Obtain exclusive use of the file */

    lfptr = &lfltab[devptr->dvminor];
    wait(lfptr->lfmutex);

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

    if (lfptr->lfstate != LF_USED) {
        signal(lfptr->lfmutex);
        return SYSERR;
    }

    /* Return SYSERR for an attempt to skip bytes beyond the byte   */
    /*  that is currently the end of the file           */

    ldptr = lfptr->lfdirptr;
    if (lfptr->lfpos > ldptr->ld_size) {
        signal(lfptr->lfmutex);
        return SYSERR;
    }

    /* If pointer is outside current block, set up new block */

    if (lfptr->lfbyte >= &lfptr->lfdblock[LF_BLKSIZ]) {

        /* Set up block for current file position */

        lfsetup(lfptr);
    }

    /* If appending a byte to the file, increment the file size.    */
    /*   Note: comparison might be equal, but should not be greater.*/

    if (lfptr->lfpos >= ldptr->ld_size) {
        ldptr->ld_size++;
        Lf_data.lf_dirdirty = TRUE;
    }

    /* Place byte in buffer and mark buffer "dirty" */

    *lfptr->lfbyte++ = ch;
    lfptr->lfpos++;
    lfptr->lfdbdirty = TRUE;

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