bget.c

The main purpose of this project is to add a new scheduling algorithm to GeekOS and to implement a s

    BGET CONFIGURATION
    ==================
*/

/*#define TestProg    20000*/	      /* Generate built-in test program
					 if defined.  The value specifies
					 how many buffer allocation attempts
					 the test program should make. */

#define SizeQuant   4		      /* Buffer allocation size quantum:
					 all buffers allocated are a
					 multiple of this size.  This
					 MUST be a power of two. */

/*#define BufDump     1*/		      /* Define this symbol to enable the
					 bpoold() function which dumps the
					 buffers in a buffer pool. */

/*#define BufValid    1*/		      /* Define this symbol to enable the
					 bpoolv() function for validating
					 a buffer pool. */ 

/*#define DumpData    1*/		      /* Define this symbol to enable the
					 bufdump() function which allows
					 dumping the contents of an allocated
					 or free buffer. */

/*#define BufStats    1*/		      /* Define this symbol to enable the
					 bstats() function which calculates
					 the total free space in the buffer
					 pool, the largest available
					 buffer, and the total space
					 currently allocated. */

/*#define FreeWipe    1*/		      /* Wipe free buffers to a guaranteed
					 pattern of garbage to trip up
					 miscreants who attempt to use
					 pointers into released buffers. */

#define BestFit     1		      /* Use a best fit algorithm when
					 searching for space for an
					 allocation request.  This uses
					 memory more efficiently, but
					 allocation will be much slower. */

/*#define BECtl	    1*/		      /* Define this symbol to enable the
					 bectl() function for automatic
					 pool space control.  */

#if defined (GEEKOS)

#include <geekos/string.h> // for memset()

// Provide an assert() macro
#include <geekos/kassert.h>
#define assert(exp) KASSERT(exp)

#else // define (GEEKOS)

#include <stdio.h>

#ifdef lint
#define NDEBUG			      /* Exits in asserts confuse lint */
/* LINTLIBRARY */                     /* Don't complain about def, no ref */
extern char *sprintf();               /* Sun includes don't define sprintf */
#endif

#include <assert.h>
#include <memory.h>

#endif // defined (GEEKOS)

#ifdef BufDump			      /* BufDump implies DumpData */
#ifndef DumpData
#define DumpData    1
#endif
#endif

#ifdef DumpData
#include <ctype.h>
#endif

/*  Declare the interface, including the requested buffer size type,
    bufsize.  */

#include <geekos/bget.h>

#define MemSize     int 	      /* Type for size arguments to memxxx()
					 functions such as memcmp(). */

/* Queue links */

struct qlinks {
    struct bfhead *flink;	      /* Forward link */
    struct bfhead *blink;	      /* Backward link */
};

/* Header in allocated and free buffers */

struct bhead {
    bufsize prevfree;		      /* Relative link back to previous
					 free buffer in memory or 0 if
					 previous buffer is allocated.	*/
    bufsize bsize;		      /* Buffer size: positive if free,
					 negative if allocated. */
};
#define BH(p)	((struct bhead *) (p))

/*  Header in directly allocated buffers (by acqfcn) */

struct bdhead {
    bufsize tsize;		      /* Total size, including overhead */
    struct bhead bh;		      /* Common header */
};
#define BDH(p)	((struct bdhead *) (p))

/* Header in free buffers */

struct bfhead {
    struct bhead bh;		      /* Common allocated/free header */
    struct qlinks ql;		      /* Links on free list */
};
#define BFH(p)	((struct bfhead *) (p))

static struct bfhead freelist = {     /* List of free buffers */
    {0, 0},
    {&freelist, &freelist}
};


#ifdef BufStats
static bufsize totalloc = 0;	      /* Total space currently allocated */
static long numget = 0, numrel = 0;   /* Number of bget() and brel() calls */
#ifdef BECtl
static long numpblk = 0;	      /* Number of pool blocks */
static long numpget = 0, numprel = 0; /* Number of block gets and rels */
static long numdget = 0, numdrel = 0; /* Number of direct gets and rels */
#endif /* BECtl */
#endif /* BufStats */

#ifdef BECtl

/* Automatic expansion block management functions */

static int (*compfcn) _((bufsize sizereq, int sequence)) = NULL;
static void *(*acqfcn) _((bufsize size)) = NULL;
static void (*relfcn) _((void *buf)) = NULL;

static bufsize exp_incr = 0;	      /* Expansion block size */
static bufsize pool_len = 0;	      /* 0: no bpool calls have been made
					 -1: not all pool blocks are
					     the same size
					 >0: (common) block size for all
					     bpool calls made so far
				      */
#endif

/*  Minimum allocation quantum: */

#define QLSize	(sizeof(struct qlinks))
#define SizeQ	((SizeQuant > QLSize) ? SizeQuant : QLSize)

#define V   (void)		      /* To denote unwanted returned values */

/* End sentinel: value placed in bsize field of dummy block delimiting
   end of pool block.  The most negative number which will  fit  in  a
   bufsize, defined in a way that the compiler will accept. */

#define ESent	((bufsize) (-(((1L << (sizeof(bufsize) * 8 - 2)) - 1) * 2) - 2))

/*  BGET  --  Allocate a buffer.  */

void *bget(requested_size)
  bufsize requested_size;
{
    bufsize size = requested_size;
    struct bfhead *b;
#ifdef BestFit
    struct bfhead *best;
#endif
    void *buf;
#ifdef BECtl
    int compactseq = 0;
#endif

    assert(size > 0);

    if (size < SizeQ) { 	      /* Need at least room for the */
	size = SizeQ;		      /*    queue links.  */
    }
#ifdef SizeQuant
#if SizeQuant > 1
    size = (size + (SizeQuant - 1)) & (~(SizeQuant - 1));
#endif
#endif

    size += sizeof(struct bhead);     /* Add overhead in allocated buffer
					 to size required. */

#ifdef BECtl
    /* If a compact function was provided in the call to bectl(), wrap
       a loop around the allocation process  to  allow	compaction  to
       intervene in case we don't find a suitable buffer in the chain. */

    while (1) {
#endif
	b = freelist.ql.flink;
#ifdef BestFit
	best = &freelist;
#endif


	/* Scan the free list searching for the first buffer big enough
	   to hold the requested size buffer. */

#ifdef BestFit
	while (b != &freelist) {
	    if (b->bh.bsize >= size) {
		if ((best == &freelist) || (b->bh.bsize < best->bh.bsize)) {
		    best = b;
		}
	    }
	    b = b->ql.flink;		  /* Link to next buffer */
	}
	b = best;
#endif /* BestFit */

	while (b != &freelist) {
	    if ((bufsize) b->bh.bsize >= size) {

		/* Buffer  is big enough to satisfy  the request.  Allocate it
		   to the caller.  We must decide whether the buffer is  large
		   enough  to  split  into  the part given to the caller and a
		   free buffer that remains on the free list, or  whether  the
		   entire  buffer  should  be  removed	from the free list and
		   given to the caller in its entirety.   We  only  split  the
		   buffer if enough room remains for a header plus the minimum
		   quantum of allocation. */

		if ((b->bh.bsize - size) > (SizeQ + (sizeof(struct bhead)))) {
		    struct bhead *ba, *bn;

		    ba = BH(((char *) b) + (b->bh.bsize - size));
		    bn = BH(((char *) ba) + size);
		    assert(bn->prevfree == b->bh.bsize);
		    /* Subtract size from length of free block. */
		    b->bh.bsize -= size;
		    /* Link allocated buffer to the previous free buffer. */
		    ba->prevfree = b->bh.bsize;
		    /* Plug negative size into user buffer. */
		    ba->bsize = -(bufsize) size;
		    /* Mark buffer after this one not preceded by free block. */
		    bn->prevfree = 0;

#ifdef BufStats
		    totalloc += size;
		    numget++;		  /* Increment number of bget() calls */
#endif
		    buf = (void *) ((((char *) ba) + sizeof(struct bhead)));
		    return buf;
		} else {
		    struct bhead *ba;

		    ba = BH(((char *) b) + b->bh.bsize);
		    assert(ba->prevfree == b->bh.bsize);

                    /* The buffer isn't big enough to split.  Give  the  whole
		       shebang to the caller and remove it from the free list. */

		    assert(b->ql.blink->ql.flink == b);
		    assert(b->ql.flink->ql.blink == b);
		    b->ql.blink->ql.flink = b->ql.flink;
		    b->ql.flink->ql.blink = b->ql.blink;

#ifdef BufStats
		    totalloc += b->bh.bsize;
		    numget++;		  /* Increment number of bget() calls */
#endif
		    /* Negate size to mark buffer allocated. */
		    b->bh.bsize = -(b->bh.bsize);

		    /* Zero the back pointer in the next buffer in memory
		       to indicate that this buffer is allocated. */
		    ba->prevfree = 0;

		    /* Give user buffer starting at queue links. */
		    buf =  (void *) &(b->ql);
		    return buf;
		}
	    }
	    b = b->ql.flink;		  /* Link to next buffer */
	}
#ifdef BECtl

        /* We failed to find a buffer.  If there's a compact  function
	   defined,  notify  it  of the size requested.  If it returns
	   true, try the allocation again. */

	if ((compfcn == NULL) || (!(*compfcn)(size, ++compactseq))) {
	    break;
	}
    }

    /* No buffer available with requested size free. */

    /* Don't give up yet -- look in the reserve supply. */

    if (acqfcn != NULL) {
	if (size > exp_incr - sizeof(struct bhead)) {

	    /* Request	is  too  large	to  fit in a single expansion
	       block.  Try to satisy it by a direct buffer acquisition. */

	    struct bdhead *bdh;

	    size += sizeof(struct bdhead) - sizeof(struct bhead);
	    if ((bdh = BDH((*acqfcn)((bufsize) size))) != NULL) {

		/*  Mark the buffer special by setting the size field
		    of its header to zero.  */
		bdh->bh.bsize = 0;
		bdh->bh.prevfree = 0;
		bdh->tsize = size;
#ifdef BufStats
		totalloc += size;
		numget++;	      /* Increment number of bget() calls */
		numdget++;	      /* Direct bget() call count */
#endif
		buf =  (void *) (bdh + 1);
		return buf;
	    }

	} else {

	    /*	Try to obtain a new expansion block */

	    void *newpool;

	    if ((newpool = (*acqfcn)((bufsize) exp_incr)) != NULL) {
		bpool(newpool, exp_incr);
                buf =  bget(requested_size);  /* This can't, I say, can't
						 get into a loop. */
		return buf;
	    }
	}
    }

    /*	Still no buffer available */

#endif /* BECtl */

    return NULL;
}

/*  BGETZ  --  Allocate a buffer and clear its contents to zero.  We clear
	       the  entire  contents  of  the buffer to zero, not just the
	       region requested by the caller. */

void *bgetz(size)
  bufsize size;
{
    char *buf = (char *) bget(size);

    if (buf != NULL) {
	struct bhead *b;
	bufsize rsize;

	b = BH(buf - sizeof(struct bhead));
	rsize = -(b->bsize);
	if (rsize == 0) {
	    struct bdhead *bd;

	    bd = BDH(buf - sizeof(struct bdhead));
	    rsize = bd->tsize - sizeof(struct bdhead);
	} else {
	    rsize -= sizeof(struct bhead);
	}
	assert(rsize >= size);
	V memset(buf, 0, (MemSize) rsize);
    }
    return ((void *) buf);
}

/*  BGETR  --  Reallocate a buffer.  This is a minimal implementation,
	       simply in terms of brel()  and  bget().	 It  could  be
	       enhanced to allow the buffer to grow into adjacent free
	       blocks and to avoid moving data unnecessarily.  */

void *bgetr(buf, size)
  void *buf;
  bufsize size;
{
    void *nbuf;
    bufsize osize;		      /* Old size of buffer */
    struct bhead *b;

    if ((nbuf = bget(size)) == NULL) { /* Acquire new buffer */
	return NULL;
    }
    if (buf == NULL) {
	return nbuf;
    }
    b = BH(((char *) buf) - sizeof(struct bhead));