lflgetc.c

Go to the documentation of this file.

/* lflgetc.c - lfgetc */

#include <xinu.h>

/*------------------------------------------------------------------------
 * lflgetc  -  Read the next byte from an open local file
 *------------------------------------------------------------------------
 */
devcall lflgetc (
      struct dentry *devptr     /* Entry in device switch table */
    )
{
    struct  lflcblk *lfptr;     /* Ptr to open file table entry */
    struct  ldentry *ldptr;     /* Ptr to file's entry in the   */
                    /*   in-memory directory    */
    int32   onebyte;        /* Next data byte in the file   */

    /* 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 EOF for any attempt to read beyond the end-of-file */

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

    /* If byte pointer is beyond the current data block, set up */
    /*  a new data block                    */

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

    /* Extract the next byte from block, update file position, and  */
    /*  return the byte to the caller               */

    onebyte = 0xff & *lfptr->lfbyte++;
    lfptr->lfpos++;
    signal(lfptr->lfmutex);
    return onebyte;
}