read.c

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/* read.c - read */

#include <xinu.h>

/*------------------------------------------------------------------------
 *  read  -  Read one or more bytes from a device
 *------------------------------------------------------------------------
 */
syscall read(
      did32     descrp,     /* Descriptor for device    */
      char      *buffer,    /* Address of buffer        */
      uint32    count       /* Length of buffer     */
    )
{
    intmask     mask;       /* Saved interrupt mask     */
    struct dentry   *devptr;    /* Entry in device switch table */
    int32       retval;     /* Value to return to caller    */

    mask = disable();
    if (isbaddev(descrp)) {
        restore(mask);
        return SYSERR;
    }
    devptr = (struct dentry *) &devtab[descrp];
    retval = (*devptr->dvread) (devptr, buffer, count);
    restore(mask);
    return retval;
}