VM: simplify slab allocator

[minix.git] / servers / mfs / cache.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:
 *   read_block:    read or write a block from the disk itself
 */

#include "fs.h"
#include <minix/u64.h>
#include <minix/bdev.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"

static void rm_lru(struct buf *bp);
static void read_block(struct buf *);

static int vmcache = 0; /* are we using vm's secondary cache? (initially not) */

static block_t super_start = 0, super_end = 0; 

/*===========================================================================*
 *                              get_block                                    *
 *===========================================================================*/
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 (ISDIRTY(bp)) 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. */
  MARKCLEAN(bp);                /* NO_DEV blocks may be marked dirty */
  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) {
        read_block(bp);
  } 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                                    *
 *===========================================================================*/
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                                   *
 *===========================================================================*/
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. */

  bit_t b, bit;
  struct super_block *sp;
  static int print_oos_msg = 1;

  /* 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;
        if (print_oos_msg)
                printf("No space on device %d/%d\n", major(sp->s_dev),
                        minor(sp->s_dev));
        print_oos_msg = 0;      /* Don't repeat message */
        return(NO_ZONE);
  }
  print_oos_msg = 1;
  if (z == sp->s_firstdatazone) sp->s_zsearch = b;      /* for next time */
  return( (zone_t) (sp->s_firstdatazone - 1) + (zone_t) b);
}

/*===========================================================================*
 *                              free_zone                                    *
 *===========================================================================*/
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;
}

/*===========================================================================*
 *                              read_block                                   *
 *===========================================================================*/
static void read_block(bp)
register struct buf *bp;        /* buffer pointer */
{
/* 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_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);
        r = bdev_read(dev, pos, bp->b_data, fs_block_size,
                BDEV_NOFLAGS);
        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 (r != (ssize_t) 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. */
                rdwt_err = r;
        }
  }
}

/*===========================================================================*
 *                              invalidate                                   *
 *===========================================================================*/
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();
}

/*===========================================================================*
 *                              block_write_ok                               *
 *===========================================================================*/
int block_write_ok(struct buf *bp)
{
        if(superblock.s_dev != bp->b_dev) return 1;

        if(bp->b_blocknr >= super_start && bp->b_blocknr <= super_end) {
                printf("MFS: blocking write to superblock on mounted filesystem dev 0x%x.\n", bp->b_dev);
                return 0;
        }

        if(superblock.s_rd_only) {
                printf("MFS: blocking write to mounted readonly filesystem 0x%x.\n", bp->b_dev);
                printf("This shouldn't happen.\n");
                return 0;
        }

        return 1;
}

/*===========================================================================*
 *                              flushall                                     *
 *===========================================================================*/
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 (ISDIRTY(bp) && bp->b_dev == dev) {
               if(!block_write_ok(bp)) {
                       printf("MFS: LATE: ignoring changes in block %d\n", bp->b_blocknr);
                       MARKCLEAN(bp);
                       continue;
               }
               dirty[ndirty++] = bp;
       }
  }
  rw_scattered(dev, dirty, ndirty, WRITING);
}

/*===========================================================================*
 *                              rw_scattered                                 *
 *===========================================================================*/
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;
  u64_t pos;
  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 bdev I/O 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;
        }
        pos = mul64u(bufq[0]->b_blocknr, fs_block_size);
        if (rw_flag == READING)
                r = bdev_gather(dev, pos, iovec, j, BDEV_NOFLAGS);
        else
                r = bdev_scatter(dev, pos, iovec, j, BDEV_NOFLAGS);

        /* Harvest the results.  The driver may have returned an error, or it
         * may have done less than what we asked for.
         */
        if (r < 0) {
                printf("MFS: I/O error %d on device %d/%d, block %u\n",
                        r, major(dev), minor(dev), bufq[0]->b_blocknr);
        }
        for (i = 0; i < j; i++) {
                bp = bufq[i];
                if (r < (ssize_t) fs_block_size) {
                        /* Transfer failed. */
                        if (i == 0) {
                                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 {
                        MARKCLEAN(bp);
                }
                r -= fs_block_size;
        }
        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                                       *
 *===========================================================================*/
static 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                                 *
 *===========================================================================*/
static 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;
  super_start = SUPER_BLOCK_BYTES / fs_block_size;
  super_end = (SUPER_BLOCK_BYTES + _MIN_BLOCK_SIZE - 1) / fs_block_size;
}

/*===========================================================================*
 *                              bufs_heuristic                               *
 *===========================================================================*/
static 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                                *
 *===========================================================================*/
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                                     *
 *===========================================================================*/
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();
}