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Commit bb207a1d authored by rsc's avatar rsc
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bio.c
+ 37
− 4
View file @ bb207a1d
// Buffer cache.
//
// The buffer cache is a linked list of buf structures
// holding cached copies of disk block contents.
// Each buf has two state bits B_BUSY and B_VALID.
// If B_BUSY is set, it means that some code is currently
// editing buf, so other code is not allowed to look at it.
// To wait for a buffer that is B_BUSY, sleep on buf.
// (See bget below.)
//
// If B_VALID is set, it means that the memory contents
// have been initialized by reading them off the disk.
// (Conversely, if B_VALID is not set, the memory contents
// of buf must be initialized, often by calling bread,
// before being used.)
//
// After making changes to a buf's memory, call bwrite to flush
// the changes out to disk, to keep the disk and memory copies
// in sync.
//
// When finished with a buffer, call brelse to release the buffer
// (i.e., clear B_BUSY), so that others can access it.
//
// Bufs that are not B_BUSY are fair game for reuse for other
// disk blocks. It is not allowed to use a buf after calling brelse.
#include "types.h"
#include "param.h"
#include "x86.h"
......@@ -10,7 +36,7 @@
struct buf buf[NBUF];
struct spinlock buf_table_lock;
// linked list of all buffers, through prev/next.
// Linked list of all buffers, through prev/next.
// bufhead->next is most recently used.
// bufhead->tail is least recently used.
struct buf bufhead;
......@@ -22,6 +48,7 @@ binit(void)
initlock(&buf_table_lock, "buf_table");
// Create linked list of buffers
bufhead.prev = &bufhead;
bufhead.next = &bufhead;
for(b = buf; b < buf+NBUF; b++){
......@@ -32,7 +59,10 @@ binit(void)
}
}
struct buf*
// Look through buffer cache for block n on device dev.
// If not found, allocate fresh block.
// In either case, return locked buffer.
static struct buf*
getblk(uint dev, uint sector)
{
struct buf *b;
......@@ -63,11 +93,12 @@ getblk(uint dev, uint sector)
return b;
}
}
panic("getblk: no buffers");
panic("bget: no buffers");
}
}
}
// Read buf's contents from disk.
struct buf*
bread(uint dev, uint sector)
{
......@@ -75,7 +106,7 @@ bread(uint dev, uint sector)
struct buf *b;
extern struct spinlock ide_lock;
b = getblk(dev, sector);
b = bget(dev, sector);
if(b->flags & B_VALID)
return b;
......@@ -89,6 +120,7 @@ bread(uint dev, uint sector)
return b;
}
// Write buf's contents to disk.
void
bwrite(struct buf *b, uint sector)
{
......@@ -103,6 +135,7 @@ bwrite(struct buf *b, uint sector)
release(&ide_lock);
}
// Release the buffer buf.
void
brelse(struct buf *b)
{
......
file.c
+ 5
− 6
View file @ bb207a1d
......@@ -41,8 +41,7 @@ filealloc(void)
return 0;
}
// Write to file descriptor;
// addr is a kernel address, pointing into some process's p->mem.
// Write to file f. Addr is kernel address.
int
filewrite(struct file *fd, char *addr, int n)
{
......@@ -64,7 +63,7 @@ filewrite(struct file *fd, char *addr, int n)
}
}
// Read from file descriptor.
// Read from file f. Addr is kernel address.
int
fileread(struct file *fd, char *addr, int n)
{
......@@ -85,7 +84,7 @@ fileread(struct file *fd, char *addr, int n)
}
}
// Close file descriptor.
// Close file f. (Decrement ref count, close when reaches 0.)
void
fileclose(struct file *fd)
{
......@@ -113,7 +112,7 @@ fileclose(struct file *fd)
}
}
// Get metadata about file descriptor.
// Get metadata about file f.
int
filestat(struct file *fd, struct stat *st)
{
......@@ -126,7 +125,7 @@ filestat(struct file *fd, struct stat *st)
return -1;
}
// Increment file descriptor reference count.
// Increment ref count for file f.
void
fileincref(struct file *fd)
{
......
fs.c
+ 60
− 6
View file @ bb207a1d
......@@ -11,8 +11,24 @@
#include "fsvar.h"
#include "dev.h"
// these are inodes currently in use
// an entry is free if count == 0
// Inode table. The inode table is an in-memory cache of the
// on-disk inode structures. If an inode in the table has a non-zero
// reference count, then some open files refer to it and it must stay
// in memory. If an inode has a zero reference count, it is only in
// memory as a cache in hopes of being used again (avoiding a disk read).
// Any inode with reference count zero can be evicted from the table.
//
// In addition to having a reference count, inodes can be marked busy
// (just like bufs), meaning that some code has logically locked the
// inode, and others are not allowed to look at it.
// This locking can last for a long
// time (for example, if the inode is busy during a disk access),
// so we don't use spin locks. Instead, if a process wants to use
// a particular inode, it must sleep(ip) to wait for it to be not busy.
// See iget below.
//
// XXX Inodes with dev == 0 exist only in memory. They have no on-disk
// representation. This functionality is used to implement pipes.
struct inode inode[NINODE];
struct spinlock inode_table_lock;
......@@ -61,6 +77,7 @@ balloc(uint dev)
return b;
}
// Free a disk block.
static void
bfree(int dev, uint b)
{
......@@ -108,6 +125,10 @@ iget(uint dev, uint inum)
if(ip->count > 0 && ip->dev == dev && ip->inum == inum){
if(ip->busy){
sleep(ip, &inode_table_lock);
// Since we droped inode_table_lock, ip might have been reused
// for some other inode entirely. Must start the scan over,
// and hopefully this time we will find the inode we want
// and it will not be busy.
goto loop;
}
ip->count++;
......@@ -142,6 +163,8 @@ iget(uint dev, uint inum)
return nip;
}
// Copy ip->d, which has changed, to disk.
// Caller must have locked ip.
void
iupdate(struct inode *ip)
{
......@@ -160,6 +183,8 @@ iupdate(struct inode *ip)
brelse(bp);
}
// Allocate a new inode with the given type
// from the file system on device dev.
struct inode*
ialloc(uint dev, short type)
{
......@@ -195,6 +220,7 @@ ialloc(uint dev, short type)
return ip;
}
// Free the given inode from its file system.
static void
ifree(struct inode *ip)
{
......@@ -202,6 +228,11 @@ ifree(struct inode *ip)
iupdate(ip);
}
// Lock the given inode (wait for it to be not busy,
// and then ip->busy).
// Caller must already hold a reference to ip.
// Otherwise, if all the references to ip go away,
// it might be reused underfoot.
void
ilock(struct inode *ip)
{
......@@ -217,8 +248,9 @@ ilock(struct inode *ip)
release(&inode_table_lock);
}
// caller is holding onto a reference to this inode, but no
// longer needs to examine or change it, so clear ip->busy.
// Caller holds reference to ip and has locked it.
// Caller no longer needs to examine / change it.
// Unlock it, but keep the reference.
void
iunlock(struct inode *ip)
{
......@@ -233,6 +265,7 @@ iunlock(struct inode *ip)
release(&inode_table_lock);
}
// Return the disk block address of the nth block in inode ip.
uint
bmap(struct inode *ip, uint bn)
{
......@@ -259,6 +292,7 @@ bmap(struct inode *ip, uint bn)
return x;
}
// Truncate the inode ip, discarding all its data blocks.
void
itrunc(struct inode *ip)
{
......@@ -286,8 +320,9 @@ itrunc(struct inode *ip)
iupdate(ip);
}
// caller is releasing a reference to this inode.
// you must have the inode lock.
// Caller holds reference to ip and has locked it,
// possibly editing it.
// Release lock and drop the reference.
void
iput(struct inode *ip)
{
......@@ -308,6 +343,8 @@ iput(struct inode *ip)
release(&inode_table_lock);
}
// Caller holds reference to ip but not lock.
// Drop reference.
void
idecref(struct inode *ip)
{
......@@ -315,6 +352,7 @@ idecref(struct inode *ip)
iput(ip);
}
// Increment reference count for ip.
void
iincref(struct inode *ip)
{
......@@ -323,6 +361,8 @@ iincref(struct inode *ip)
iunlock(ip);
}
// Copy stat information from inode.
// XXX Assumes inode is from disk file system.
void
stati(struct inode *ip, struct stat *st)
{
......@@ -335,6 +375,8 @@ stati(struct inode *ip, struct stat *st)
#define min(a, b) ((a) < (b) ? (a) : (b))
// Read data from inode.
// XXX Assumes inode is from disk file system.
int
readi(struct inode *ip, char *dst, uint off, uint n)
{
......@@ -361,6 +403,7 @@ readi(struct inode *ip, char *dst, uint off, uint n)
return target - n;
}
// Allocate the nth block in inode ip if necessary.
static int
newblock(struct inode *ip, uint lbn)
{
......@@ -396,6 +439,8 @@ newblock(struct inode *ip, uint lbn)
return 0;
}
// Write data to inode.
// XXX Assumes inode is from disk file system.
int
writei(struct inode *ip, char *addr, uint off, uint n)
{
......@@ -551,6 +596,8 @@ namei(char *path, int mode, uint *ret_off,
}
}
// Write a new directory entry (name, ino) into the directory dp.
// Caller must have locked dp.
void
wdir(struct inode *dp, char *name, uint ino)
{
......@@ -575,6 +622,8 @@ wdir(struct inode *dp, char *name, uint ino)
panic("wdir write");
}
// Create the path cp and return its locked inode structure.
// If cp already exists, return 0.
struct inode*
mknod(char *cp, short type, short major, short minor)
{
......@@ -591,6 +640,9 @@ mknod(char *cp, short type, short major, short minor)
return ip;
}
// Create a new inode named name inside dp
// and return its locked inode structure.
// If name already exists, return 0.
struct inode*
mknod1(struct inode *dp, char *name, short type, short major, short minor)
{
......@@ -611,6 +663,7 @@ mknod1(struct inode *dp, char *name, short type, short major, short minor)
return ip;
}
// Unlink the inode named cp.
int
unlink(char *cp)
{
......@@ -649,6 +702,7 @@ unlink(char *cp)
return 0;
}
// Create the path new as a link to the same inode as old.
int
link(char *name1, char *name2)
{
......
ide.c
+ 7
− 0
View file @ bb207a1d
......@@ -17,6 +17,12 @@
#define IDE_CMD_READ 0x20
#define IDE_CMD_WRITE 0x30
// IDE request queue.
// The next request will be stored in request[head],
// and the request currently being served by the disk
// is request[tail].
// Must hold ide_lock while manipulating queue.
struct ide_request {
int diskno;
uint secno;
......@@ -28,6 +34,7 @@ struct ide_request {
struct ide_request request[NREQUEST];
int head, tail;
struct spinlock ide_lock;
int disk_1_present;
int disk_channel;
......
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