heapfuncs.c

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/*-------------------------------------------------------------------------
 *
 * heapfuncs.c
 *    Functions to investigate heap pages
 *
 * We check the input to these functions for corrupt pointers etc. that
 * might cause crashes, but at the same time we try to print out as much
 * information as possible, even if it's nonsense. That's because if a
 * page is corrupt, we don't know why and how exactly it is corrupt, so we
 * let the user judge it.
 *
 * These functions are restricted to superusers for the fear of introducing
 * security holes if the input checking isn't as water-tight as it should be.
 * You'd need to be superuser to obtain a raw page image anyway, so
 * there's hardly any use case for using these without superuser-rights
 * anyway.
 *
 * Copyright (c) 2007-2013, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    contrib/pageinspect/heapfuncs.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "funcapi.h"
#include "utils/builtins.h"
#include "miscadmin.h"

Datum       heap_page_items(PG_FUNCTION_ARGS);


/*
 * bits_to_text
 *
 * Converts a bits8-array of 'len' bits to a human-readable
 * c-string representation.
 */
static char *
bits_to_text(bits8 *bits, int len)
{
    int         i;
    char       *str;

    str = palloc(len + 1);

    for (i = 0; i < len; i++)
        str[i] = (bits[(i / 8)] & (1 << (i % 8))) ? '1' : '0';

    str[i] = '\0';

    return str;
}


/*
 * heap_page_items
 *
 * Allows inspection of line pointers and tuple headers of a heap page.
 */
PG_FUNCTION_INFO_V1(heap_page_items);

typedef struct heap_page_items_state
{
    TupleDesc   tupd;
    Page        page;
    uint16      offset;
} heap_page_items_state;

Datum
heap_page_items(PG_FUNCTION_ARGS)
{
    bytea      *raw_page = PG_GETARG_BYTEA_P(0);
    heap_page_items_state *inter_call_data = NULL;
    FuncCallContext *fctx;
    int         raw_page_size;

    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 (errmsg("must be superuser to use raw page functions"))));

    raw_page_size = VARSIZE(raw_page) - VARHDRSZ;

    if (SRF_IS_FIRSTCALL())
    {
        TupleDesc   tupdesc;
        MemoryContext mctx;

        if (raw_page_size < SizeOfPageHeaderData)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                  errmsg("input page too small (%d bytes)", raw_page_size)));

        fctx = SRF_FIRSTCALL_INIT();
        mctx = MemoryContextSwitchTo(fctx->multi_call_memory_ctx);

        inter_call_data = palloc(sizeof(heap_page_items_state));

        /* Build a tuple descriptor for our result type */
        if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
            elog(ERROR, "return type must be a row type");

        inter_call_data->tupd = tupdesc;

        inter_call_data->offset = FirstOffsetNumber;
        inter_call_data->page = VARDATA(raw_page);

        fctx->max_calls = PageGetMaxOffsetNumber(inter_call_data->page);
        fctx->user_fctx = inter_call_data;

        MemoryContextSwitchTo(mctx);
    }

    fctx = SRF_PERCALL_SETUP();
    inter_call_data = fctx->user_fctx;

    if (fctx->call_cntr < fctx->max_calls)
    {
        Page        page = inter_call_data->page;
        HeapTuple   resultTuple;
        Datum       result;
        ItemId      id;
        Datum       values[13];
        bool        nulls[13];
        uint16      lp_offset;
        uint16      lp_flags;
        uint16      lp_len;

        memset(nulls, 0, sizeof(nulls));

        /* Extract information from the line pointer */

        id = PageGetItemId(page, inter_call_data->offset);

        lp_offset = ItemIdGetOffset(id);
        lp_flags = ItemIdGetFlags(id);
        lp_len = ItemIdGetLength(id);

        values[0] = UInt16GetDatum(inter_call_data->offset);
        values[1] = UInt16GetDatum(lp_offset);
        values[2] = UInt16GetDatum(lp_flags);
        values[3] = UInt16GetDatum(lp_len);

        /*
         * We do just enough validity checking to make sure we don't reference
         * data outside the page passed to us. The page could be corrupt in
         * many other ways, but at least we won't crash.
         */
        if (ItemIdHasStorage(id) &&
            lp_len >= sizeof(HeapTupleHeader) &&
            lp_offset == MAXALIGN(lp_offset) &&
            lp_offset + lp_len <= raw_page_size)
        {
            HeapTupleHeader tuphdr;
            int         bits_len;

            /* Extract information from the tuple header */

            tuphdr = (HeapTupleHeader) PageGetItem(page, id);

            values[4] = UInt32GetDatum(HeapTupleHeaderGetXmin(tuphdr));
            values[5] = UInt32GetDatum(HeapTupleHeaderGetRawXmax(tuphdr));
            values[6] = UInt32GetDatum(HeapTupleHeaderGetRawCommandId(tuphdr)); /* shared with xvac */
            values[7] = PointerGetDatum(&tuphdr->t_ctid);
            values[8] = UInt32GetDatum(tuphdr->t_infomask2);
            values[9] = UInt32GetDatum(tuphdr->t_infomask);
            values[10] = UInt8GetDatum(tuphdr->t_hoff);

            /*
             * We already checked that the item as is completely within the
             * raw page passed to us, with the length given in the line
             * pointer.. Let's check that t_hoff doesn't point over lp_len,
             * before using it to access t_bits and oid.
             */
            if (tuphdr->t_hoff >= sizeof(HeapTupleHeader) &&
                tuphdr->t_hoff <= lp_len)
            {
                if (tuphdr->t_infomask & HEAP_HASNULL)
                {
                    bits_len = tuphdr->t_hoff -
                        (((char *) tuphdr->t_bits) -((char *) tuphdr));

                    values[11] = CStringGetTextDatum(
                                 bits_to_text(tuphdr->t_bits, bits_len * 8));
                }
                else
                    nulls[11] = true;

                if (tuphdr->t_infomask & HEAP_HASOID)
                    values[12] = HeapTupleHeaderGetOid(tuphdr);
                else
                    nulls[12] = true;
            }
            else
            {
                nulls[11] = true;
                nulls[12] = true;
            }
        }
        else
        {
            /*
             * The line pointer is not used, or it's invalid. Set the rest of
             * the fields to NULL
             */
            int         i;

            for (i = 4; i <= 12; i++)
                nulls[i] = true;
        }

        /* Build and return the result tuple. */
        resultTuple = heap_form_tuple(inter_call_data->tupd, values, nulls);
        result = HeapTupleGetDatum(resultTuple);

        inter_call_data->offset++;

        SRF_RETURN_NEXT(fctx, result);
    }
    else
        SRF_RETURN_DONE(fctx);
}