File:bio.c - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

4700 #

4701 /*

4702  */

4703

4704 #include "../param.h"

4705 #include "../user.h"

4706 #include "../buf.h"

4707 #include "../conf.h"

4708 #include "../systm.h"

4709 #include "../proc.h"

4710 #include "../seg.h"

4711

4712 /*

4713  * This is the set of buffres proper, whose heads

4714  * were declared in buf.h. There can exist buffer

4715  * headers not pointing here that are used purely

4716  * as arguments to the I/O routines to describe

4717  * I/O to be done-- e.g. swbuf, just below, for

4718  * swapping.

4719  */

4720 char buffers[NBUF][514];

• 设备缓存数组,参见 设备缓存管理

4721 struct buf swbuf;

4722

4723 /*

4724  * Declarations of the tables for the magtape devices;

4725  * see bdwrite.

4726  */

4727 int tmtab;

4728 int httab;

• 指向 磁带设备 的指针
• 类型为 struct devtab
• 参见 bdwrite

4729

4730 /*

4731  * The following several routines allocate and free

4732  * buffers with various side effects. In general the

4733  * arguments to an allocate routine are a device and

4734  * a block number, and the value is a pointer to

4735  * the buffer header; the buffer is marked "busy"

4736  * so that no one else can touch it. If the block was

4737  * already in core, no I/O need be done; if it is

4738  * already busy, the process waits until it becomes free.

4739  * The following routines allocate a buffer:

4740  * getblk

4741  * bread

4742  * breada

4743  * Eventually the buffer must be released, possibly with the

4744  * side effect of writing it out, by using one of

4745  * bwrite

4746  * bdwrite

4747  * bawrite

4748  * brelse

4749  */