code:passc - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

6510

6511 /* Pass back c to the user at his location u_base;

6512 * update u_base, u_count, and u_offset. Return -1

6513 * on the last character of the user’s read.

6514 * u_base is in the user address space unless u_segflg

6515 * is set.

6516 */

6517 passc(c)

6518 char c;

6519 {

6520

6522 *u.u_base =c; else

6523 if(subyte(u.u_base, c) < 0) {

6524 u.u_error = EFAULT;

6525 return(-1);

6526 }

若目标地址空间为核心态地址空间，则直接向目标地址写入字节

若目标地址空间为用户态地址空间，则调用subyte 向目标地址写入字节
若出错

抛出错误，错误代码为EFAULT

返回-1

6527 u.u_count--;

6528 if(++u.u_offset[1] == 0)

6529 u.u_offset[0]++;

修改相应参数

u.u_count

u.u_offset

u.u_base

参看user

6531 return(u.u_count == 0? -1: 0);

若u.u_count==0(写入任务完成)，则返回-1

否则，返回0

6532 }

6533 /* ------------------------- */