code:struct devtab - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

4537

4538 /*

4539 * Each block device has a devtab, which contains private

4540 * state stuff and 2 list heads: the b_forw/b_back list,

4541 * which is doubly linked and has all the buffers currently

4542 * associated with the major device;

4543 * and the d_actf/d_actl list, which is private to the

4544 * device but in fact is always used for the head and tail

4545 * of the I/O queue for the device.

4546 * Various routines in bio.c look at b_forw/b_back

4547 * (notice they are the same as in the buf structure)

4548 * but the rest is private to each device driver.

4549 */

4550

4551 struct devtab

4552 {

4553 char d_active; /* busy flag */

标志设备是否启动

4554 char d_errcnt; /* error count (for recovery)*/

累计I/O错误次数

4555 struct buf *b_forw; /* first buffer for this dev */

4556 struct buf *b_back; /* last buffer for this dev */

设备队列的队列头尾

4557 struct buf *d_actf; /* head of I/O queue */

4558 struct buf *d_actl; /* tail of I/O queue */

设备I/O队列的队列头尾

4559 };

4560 /* ------------------------- */