minix/servers/mfs/cache.c
Ben Gras 49532259e5 mfs: improve & simplify secondary cache logic
. fixes "!" errors when booting from cd
2011-09-23 15:02:20 +00:00

642 lines
19 KiB
C

/* The file system maintains a buffer cache to reduce the number of disk
* accesses needed. Whenever a read or write to the disk is done, a check is
* first made to see if the block is in the cache. This file manages the
* cache.
*
* The entry points into this file are:
* get_block: request to fetch a block for reading or writing from cache
* put_block: return a block previously requested with get_block
* alloc_zone: allocate a new zone (to increase the length of a file)
* free_zone: release a zone (when a file is removed)
* invalidate: remove all the cache blocks on some device
*
* Private functions:
* rw_block: read or write a block from the disk itself
*/
#include "fs.h"
#include <minix/u64.h>
#include <sys/param.h>
#include <stdlib.h>
#include <assert.h>
#include <minix/libminixfs.h>
#include <math.h>
#include "buf.h"
#include "super.h"
#include "inode.h"
FORWARD _PROTOTYPE( void rm_lru, (struct buf *bp) );
FORWARD _PROTOTYPE( void rw_block, (struct buf *, int) );
PRIVATE int vmcache = 0; /* are we using vm's secondary cache? (initially not) */
/*===========================================================================*
* get_block *
*===========================================================================*/
PUBLIC struct buf *get_block(
register dev_t dev, /* on which device is the block? */
register block_t block, /* which block is wanted? */
int only_search /* if NO_READ, don't read, else act normal */
)
{
/* Check to see if the requested block is in the block cache. If so, return
* a pointer to it. If not, evict some other block and fetch it (unless
* 'only_search' is 1). All the blocks in the cache that are not in use
* are linked together in a chain, with 'front' pointing to the least recently
* used block and 'rear' to the most recently used block. If 'only_search' is
* 1, the block being requested will be overwritten in its entirety, so it is
* only necessary to see if it is in the cache; if it is not, any free buffer
* will do. It is not necessary to actually read the block in from disk.
* If 'only_search' is PREFETCH, the block need not be read from the disk,
* and the device is not to be marked on the block, so callers can tell if
* the block returned is valid.
* In addition to the LRU chain, there is also a hash chain to link together
* blocks whose block numbers end with the same bit strings, for fast lookup.
*/
int b;
static struct buf *bp, *prev_ptr;
u64_t yieldid = VM_BLOCKID_NONE, getid = make64(dev, block);
assert(buf_hash);
assert(buf);
assert(nr_bufs > 0);
ASSERT(fs_block_size > 0);
/* Search the hash chain for (dev, block). Do_read() can use
* get_block(NO_DEV ...) to get an unnamed block to fill with zeros when
* someone wants to read from a hole in a file, in which case this search
* is skipped
*/
if (dev != NO_DEV) {
b = BUFHASH(block);
bp = buf_hash[b];
while (bp != NULL) {
if (bp->b_blocknr == block && bp->b_dev == dev) {
/* Block needed has been found. */
if (bp->b_count == 0) rm_lru(bp);
bp->b_count++; /* record that block is in use */
ASSERT(bp->b_bytes == fs_block_size);
ASSERT(bp->b_dev == dev);
ASSERT(bp->b_dev != NO_DEV);
ASSERT(bp->bp);
return(bp);
} else {
/* This block is not the one sought. */
bp = bp->b_hash; /* move to next block on hash chain */
}
}
}
/* Desired block is not on available chain. Take oldest block ('front'). */
if ((bp = front) == NULL) panic("all buffers in use: %d", nr_bufs);
if(bp->b_bytes < fs_block_size) {
ASSERT(!bp->bp);
ASSERT(bp->b_bytes == 0);
if(!(bp->bp = alloc_contig( (size_t) fs_block_size, 0, NULL))) {
printf("MFS: couldn't allocate a new block.\n");
for(bp = front;
bp && bp->b_bytes < fs_block_size; bp = bp->b_next)
;
if(!bp) {
panic("no buffer available");
}
} else {
bp->b_bytes = fs_block_size;
}
}
ASSERT(bp);
ASSERT(bp->bp);
ASSERT(bp->b_bytes == fs_block_size);
ASSERT(bp->b_count == 0);
rm_lru(bp);
/* Remove the block that was just taken from its hash chain. */
b = BUFHASH(bp->b_blocknr);
prev_ptr = buf_hash[b];
if (prev_ptr == bp) {
buf_hash[b] = bp->b_hash;
} else {
/* The block just taken is not on the front of its hash chain. */
while (prev_ptr->b_hash != NULL)
if (prev_ptr->b_hash == bp) {
prev_ptr->b_hash = bp->b_hash; /* found it */
break;
} else {
prev_ptr = prev_ptr->b_hash; /* keep looking */
}
}
/* If the block taken is dirty, make it clean by writing it to the disk.
* Avoid hysteresis by flushing all other dirty blocks for the same device.
*/
if (bp->b_dev != NO_DEV) {
if (bp->b_dirt == DIRTY) flushall(bp->b_dev);
/* Are we throwing out a block that contained something?
* Give it to VM for the second-layer cache.
*/
yieldid = make64(bp->b_dev, bp->b_blocknr);
assert(bp->b_bytes == fs_block_size);
bp->b_dev = NO_DEV;
}
/* Fill in block's parameters and add it to the hash chain where it goes. */
bp->b_dev = dev; /* fill in device number */
bp->b_blocknr = block; /* fill in block number */
bp->b_count++; /* record that block is being used */
b = BUFHASH(bp->b_blocknr);
bp->b_hash = buf_hash[b];
buf_hash[b] = bp; /* add to hash list */
if(dev == NO_DEV) {
if(vmcache && cmp64(yieldid, VM_BLOCKID_NONE) != 0) {
vm_yield_block_get_block(yieldid, VM_BLOCKID_NONE,
bp->bp, fs_block_size);
}
return(bp); /* If the caller wanted a NO_DEV block, work is done. */
}
/* Go get the requested block unless searching or prefetching. */
if(only_search == PREFETCH || only_search == NORMAL) {
/* Block is not found in our cache, but we do want it
* if it's in the vm cache.
*/
if(vmcache) {
/* If we can satisfy the PREFETCH or NORMAL request
* from the vm cache, work is done.
*/
if(vm_yield_block_get_block(yieldid, getid,
bp->bp, fs_block_size) == OK) {
return bp;
}
}
}
if(only_search == PREFETCH) {
/* PREFETCH: don't do i/o. */
bp->b_dev = NO_DEV;
} else if (only_search == NORMAL) {
rw_block(bp, READING);
} else if(only_search == NO_READ) {
/* we want this block, but its contents
* will be overwritten. VM has to forget
* about it.
*/
if(vmcache) {
vm_forgetblock(getid);
}
} else
panic("unexpected only_search value: %d", only_search);
assert(bp->bp);
return(bp); /* return the newly acquired block */
}
/*===========================================================================*
* put_block *
*===========================================================================*/
PUBLIC void put_block(bp, block_type)
register struct buf *bp; /* pointer to the buffer to be released */
int block_type; /* INODE_BLOCK, DIRECTORY_BLOCK, or whatever */
{
/* Return a block to the list of available blocks. Depending on 'block_type'
* it may be put on the front or rear of the LRU chain. Blocks that are
* expected to be needed again shortly (e.g., partially full data blocks)
* go on the rear; blocks that are unlikely to be needed again shortly
* (e.g., full data blocks) go on the front. Blocks whose loss can hurt
* the integrity of the file system (e.g., inode blocks) are written to
* disk immediately if they are dirty.
*/
if (bp == NULL) return; /* it is easier to check here than in caller */
bp->b_count--; /* there is one use fewer now */
if (bp->b_count != 0) return; /* block is still in use */
bufs_in_use--; /* one fewer block buffers in use */
/* Put this block back on the LRU chain. If the ONE_SHOT bit is set in
* 'block_type', the block is not likely to be needed again shortly, so put
* it on the front of the LRU chain where it will be the first one to be
* taken when a free buffer is needed later.
*/
if (bp->b_dev == DEV_RAM || (block_type & ONE_SHOT)) {
/* Block probably won't be needed quickly. Put it on front of chain.
* It will be the next block to be evicted from the cache.
*/
bp->b_prev = NULL;
bp->b_next = front;
if (front == NULL)
rear = bp; /* LRU chain was empty */
else
front->b_prev = bp;
front = bp;
}
else {
/* Block probably will be needed quickly. Put it on rear of chain.
* It will not be evicted from the cache for a long time.
*/
bp->b_prev = rear;
bp->b_next = NULL;
if (rear == NULL)
front = bp;
else
rear->b_next = bp;
rear = bp;
}
}
/*===========================================================================*
* alloc_zone *
*===========================================================================*/
PUBLIC zone_t alloc_zone(
dev_t dev, /* device where zone wanted */
zone_t z /* try to allocate new zone near this one */
)
{
/* Allocate a new zone on the indicated device and return its number. */
int major, minor;
bit_t b, bit;
struct super_block *sp;
/* Note that the routine alloc_bit() returns 1 for the lowest possible
* zone, which corresponds to sp->s_firstdatazone. To convert a value
* between the bit number, 'b', used by alloc_bit() and the zone number, 'z',
* stored in the inode, use the formula:
* z = b + sp->s_firstdatazone - 1
* Alloc_bit() never returns 0, since this is used for NO_BIT (failure).
*/
sp = get_super(dev);
/* If z is 0, skip initial part of the map known to be fully in use. */
if (z == sp->s_firstdatazone) {
bit = sp->s_zsearch;
} else {
bit = (bit_t) (z - (sp->s_firstdatazone - 1));
}
b = alloc_bit(sp, ZMAP, bit);
if (b == NO_BIT) {
err_code = ENOSPC;
major = (int) (sp->s_dev >> MAJOR) & BYTE;
minor = (int) (sp->s_dev >> MINOR) & BYTE;
printf("No space on device %d/%d\n", major, minor);
return(NO_ZONE);
}
if (z == sp->s_firstdatazone) sp->s_zsearch = b; /* for next time */
return( (zone_t) (sp->s_firstdatazone - 1) + (zone_t) b);
}
/*===========================================================================*
* free_zone *
*===========================================================================*/
PUBLIC void free_zone(
dev_t dev, /* device where zone located */
zone_t numb /* zone to be returned */
)
{
/* Return a zone. */
register struct super_block *sp;
bit_t bit;
/* Locate the appropriate super_block and return bit. */
sp = get_super(dev);
if (numb < sp->s_firstdatazone || numb >= sp->s_zones) return;
bit = (bit_t) (numb - (zone_t) (sp->s_firstdatazone - 1));
free_bit(sp, ZMAP, bit);
if (bit < sp->s_zsearch) sp->s_zsearch = bit;
}
/*===========================================================================*
* rw_block *
*===========================================================================*/
PRIVATE void rw_block(bp, rw_flag)
register struct buf *bp; /* buffer pointer */
int rw_flag; /* READING or WRITING */
{
/* Read or write a disk block. This is the only routine in which actual disk
* I/O is invoked. If an error occurs, a message is printed here, but the error
* is not reported to the caller. If the error occurred while purging a block
* from the cache, it is not clear what the caller could do about it anyway.
*/
int r, op, op_failed;
u64_t pos;
dev_t dev;
op_failed = 0;
if ( (dev = bp->b_dev) != NO_DEV) {
pos = mul64u(bp->b_blocknr, fs_block_size);
op = (rw_flag == READING ? MFS_DEV_READ : MFS_DEV_WRITE);
r = block_dev_io(op, dev, SELF_E, bp->b_data, pos, fs_block_size);
if (r < 0) {
printf("MFS(%d) I/O error on device %d/%d, block %u\n",
SELF_E, major(dev), minor(dev), bp->b_blocknr);
op_failed = 1;
} else if( (unsigned) r != fs_block_size) {
r = END_OF_FILE;
op_failed = 1;
}
if (op_failed) {
bp->b_dev = NO_DEV; /* invalidate block */
/* Report read errors to interested parties. */
if (rw_flag == READING) rdwt_err = r;
}
}
bp->b_dirt = CLEAN;
}
/*===========================================================================*
* invalidate *
*===========================================================================*/
PUBLIC void invalidate(
dev_t device /* device whose blocks are to be purged */
)
{
/* Remove all the blocks belonging to some device from the cache. */
register struct buf *bp;
for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++)
if (bp->b_dev == device) bp->b_dev = NO_DEV;
vm_forgetblocks();
}
/*===========================================================================*
* flushall *
*===========================================================================*/
PUBLIC void flushall(
dev_t dev /* device to flush */
)
{
/* Flush all dirty blocks for one device. */
register struct buf *bp;
static struct buf **dirty; /* static so it isn't on stack */
static unsigned int dirtylistsize = 0;
int ndirty;
if(dirtylistsize != nr_bufs) {
if(dirtylistsize > 0) {
assert(dirty != NULL);
free(dirty);
}
if(!(dirty = malloc(sizeof(dirty[0])*nr_bufs)))
panic("couldn't allocate dirty buf list");
dirtylistsize = nr_bufs;
}
for (bp = &buf[0], ndirty = 0; bp < &buf[nr_bufs]; bp++)
if (bp->b_dirt == DIRTY && bp->b_dev == dev) dirty[ndirty++] = bp;
rw_scattered(dev, dirty, ndirty, WRITING);
}
/*===========================================================================*
* rw_scattered *
*===========================================================================*/
PUBLIC void rw_scattered(
dev_t dev, /* major-minor device number */
struct buf **bufq, /* pointer to array of buffers */
int bufqsize, /* number of buffers */
int rw_flag /* READING or WRITING */
)
{
/* Read or write scattered data from a device. */
register struct buf *bp;
int gap;
register int i;
register iovec_t *iop;
static iovec_t *iovec = NULL;
int j, r;
STATICINIT(iovec, NR_IOREQS);
/* (Shell) sort buffers on b_blocknr. */
gap = 1;
do
gap = 3 * gap + 1;
while (gap <= bufqsize);
while (gap != 1) {
gap /= 3;
for (j = gap; j < bufqsize; j++) {
for (i = j - gap;
i >= 0 && bufq[i]->b_blocknr > bufq[i + gap]->b_blocknr;
i -= gap) {
bp = bufq[i];
bufq[i] = bufq[i + gap];
bufq[i + gap] = bp;
}
}
}
/* Set up I/O vector and do I/O. The result of dev_io is OK if everything
* went fine, otherwise the error code for the first failed transfer.
*/
while (bufqsize > 0) {
for (j = 0, iop = iovec; j < NR_IOREQS && j < bufqsize; j++, iop++) {
bp = bufq[j];
if (bp->b_blocknr != (block_t) bufq[0]->b_blocknr + j) break;
iop->iov_addr = (vir_bytes) bp->b_data;
iop->iov_size = (vir_bytes) fs_block_size;
}
r = block_dev_io(rw_flag == WRITING ? MFS_DEV_SCATTER : MFS_DEV_GATHER,
dev, SELF_E, iovec,
mul64u(bufq[0]->b_blocknr, fs_block_size), j);
/* Harvest the results. Dev_io reports the first error it may have
* encountered, but we only care if it's the first block that failed.
*/
for (i = 0, iop = iovec; i < j; i++, iop++) {
bp = bufq[i];
if (iop->iov_size != 0) {
/* Transfer failed. An error? Do we care? */
if (r != OK && i == 0) {
printf(
"MFS: I/O error on device %d/%d, block %u\n",
major(dev), minor(dev), bp->b_blocknr);
bp->b_dev = NO_DEV; /* invalidate block */
vm_forgetblocks();
}
break;
}
if (rw_flag == READING) {
bp->b_dev = dev; /* validate block */
put_block(bp, PARTIAL_DATA_BLOCK);
} else {
bp->b_dirt = CLEAN;
}
}
bufq += i;
bufqsize -= i;
if (rw_flag == READING) {
/* Don't bother reading more than the device is willing to
* give at this time. Don't forget to release those extras.
*/
while (bufqsize > 0) {
put_block(*bufq++, PARTIAL_DATA_BLOCK);
bufqsize--;
}
}
if (rw_flag == WRITING && i == 0) {
/* We're not making progress, this means we might keep
* looping. Buffers remain dirty if un-written. Buffers are
* lost if invalidate()d or LRU-removed while dirty. This
* is better than keeping unwritable blocks around forever..
*/
break;
}
}
}
/*===========================================================================*
* rm_lru *
*===========================================================================*/
PRIVATE void rm_lru(bp)
struct buf *bp;
{
/* Remove a block from its LRU chain. */
struct buf *next_ptr, *prev_ptr;
bufs_in_use++;
next_ptr = bp->b_next; /* successor on LRU chain */
prev_ptr = bp->b_prev; /* predecessor on LRU chain */
if (prev_ptr != NULL)
prev_ptr->b_next = next_ptr;
else
front = next_ptr; /* this block was at front of chain */
if (next_ptr != NULL)
next_ptr->b_prev = prev_ptr;
else
rear = prev_ptr; /* this block was at rear of chain */
}
/*===========================================================================*
* cache_resize *
*===========================================================================*/
PRIVATE void cache_resize(unsigned int blocksize, unsigned int bufs)
{
struct buf *bp;
struct inode *rip;
#define MINBUFS 10
assert(blocksize > 0);
assert(bufs >= MINBUFS);
for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++)
if(bp->b_count != 0) panic("change blocksize with buffer in use");
for (rip = &inode[0]; rip < &inode[NR_INODES]; rip++)
if (rip->i_count > 0) panic("change blocksize with inode in use");
buf_pool(bufs);
fs_block_size = blocksize;
}
/*===========================================================================*
* bufs_heuristic *
*===========================================================================*/
PRIVATE int bufs_heuristic(struct super_block *sp)
{
u32_t btotal, bfree, bused;
blockstats(&btotal, &bfree, &bused);
return fs_bufs_heuristic(MINBUFS, btotal, bfree,
sp->s_block_size, major(sp->s_dev));
}
/*===========================================================================*
* set_blocksize *
*===========================================================================*/
PUBLIC void set_blocksize(struct super_block *sp)
{
int bufs;
cache_resize(sp->s_block_size, MINBUFS);
bufs = bufs_heuristic(sp);
cache_resize(sp->s_block_size, bufs);
/* Decide whether to use seconday cache or not.
* Only do this if
* - it's available, and
* - use of it hasn't been disabled for this fs, and
* - our main FS device isn't a memory device
*/
vmcache = 0;
if(vm_forgetblock(VM_BLOCKID_NONE) != ENOSYS &&
may_use_vmcache && major(sp->s_dev) != MEMORY_MAJOR) {
vmcache = 1;
}
}
/*===========================================================================*
* buf_pool *
*===========================================================================*/
PUBLIC void buf_pool(int new_nr_bufs)
{
/* Initialize the buffer pool. */
register struct buf *bp;
assert(new_nr_bufs >= MINBUFS);
if(nr_bufs > 0) {
assert(buf);
(void) fs_sync();
for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++) {
if(bp->bp) {
assert(bp->b_bytes > 0);
free_contig(bp->bp, bp->b_bytes);
}
}
}
if(buf)
free(buf);
if(!(buf = calloc(sizeof(buf[0]), new_nr_bufs)))
panic("couldn't allocate buf list (%d)", new_nr_bufs);
if(buf_hash)
free(buf_hash);
if(!(buf_hash = calloc(sizeof(buf_hash[0]), new_nr_bufs)))
panic("couldn't allocate buf hash list (%d)", new_nr_bufs);
nr_bufs = new_nr_bufs;
bufs_in_use = 0;
front = &buf[0];
rear = &buf[nr_bufs - 1];
for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++) {
bp->b_blocknr = NO_BLOCK;
bp->b_dev = NO_DEV;
bp->b_next = bp + 1;
bp->b_prev = bp - 1;
bp->bp = NULL;
bp->b_bytes = 0;
}
front->b_prev = NULL;
rear->b_next = NULL;
for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++) bp->b_hash = bp->b_next;
buf_hash[0] = front;
vm_forgetblocks();
}