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postgres/contrib/pageinspect/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) 2007-2018, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/pageinspect/heapfuncs.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "pageinspect.h"
#include "access/htup_details.h"
#include "funcapi.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/rel.h"
/*
* 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;
}
/*
* text_to_bits
*
* Converts a c-string representation of bits into a bits8-array. This is
* the reverse operation of previous routine.
*/
static bits8 *
text_to_bits(char *str, int len)
{
bits8 *bits;
int off = 0;
char byte = 0;
bits = palloc(len + 1);
while (off < len)
{
if (off % 8 == 0)
byte = 0;
if ((str[off] == '0') || (str[off] == '1'))
byte = byte | ((str[off] - '0') << off % 8);
else
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("illegal character '%c' in t_bits string", str[off])));
if (off % 8 == 7)
bits[off / 8] = byte;
off++;
}
return bits;
}
/*
* 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[14];
bool nulls[14];
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 >= MinHeapTupleSize &&
lp_offset == MAXALIGN(lp_offset) &&
lp_offset + lp_len <= raw_page_size)
{
HeapTupleHeader tuphdr;
bytea *tuple_data_bytea;
int tuple_data_len;
/* Extract information from the tuple header */
tuphdr = (HeapTupleHeader) PageGetItem(page, id);
values[4] = UInt32GetDatum(HeapTupleHeaderGetRawXmin(tuphdr));
values[5] = UInt32GetDatum(HeapTupleHeaderGetRawXmax(tuphdr));
/* shared with xvac */
values[6] = UInt32GetDatum(HeapTupleHeaderGetRawCommandId(tuphdr));
values[7] = PointerGetDatum(&tuphdr->t_ctid);
values[8] = UInt32GetDatum(tuphdr->t_infomask2);
values[9] = UInt32GetDatum(tuphdr->t_infomask);
values[10] = UInt8GetDatum(tuphdr->t_hoff);
/* Copy raw tuple data into bytea attribute */
tuple_data_len = lp_len - tuphdr->t_hoff;
tuple_data_bytea = (bytea *) palloc(tuple_data_len + VARHDRSZ);
SET_VARSIZE(tuple_data_bytea, tuple_data_len + VARHDRSZ);
memcpy(VARDATA(tuple_data_bytea), (char *) tuphdr + tuphdr->t_hoff,
tuple_data_len);
values[13] = PointerGetDatum(tuple_data_bytea);
/*
* We already checked that the item 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 >= SizeofHeapTupleHeader &&
tuphdr->t_hoff <= lp_len &&
tuphdr->t_hoff == MAXALIGN(tuphdr->t_hoff))
{
if (tuphdr->t_infomask & HEAP_HASNULL)
{
int bits_len;
bits_len =
BITMAPLEN(HeapTupleHeaderGetNatts(tuphdr)) * BITS_PER_BYTE;
values[11] = CStringGetTextDatum(
bits_to_text(tuphdr->t_bits, bits_len));
}
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 <= 13; 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);
}
/*
* tuple_data_split_internal
*
* Split raw tuple data taken directly from a page into an array of bytea
* elements. This routine does a lookup on NULL values and creates array
* elements accordingly. This is a reimplementation of nocachegetattr()
* in heaptuple.c simplified for educational purposes.
*/
static Datum
tuple_data_split_internal(Oid relid, char *tupdata,
uint16 tupdata_len, uint16 t_infomask,
uint16 t_infomask2, bits8 *t_bits,
bool do_detoast)
{
ArrayBuildState *raw_attrs;
int nattrs;
int i;
int off = 0;
Relation rel;
TupleDesc tupdesc;
/* Get tuple descriptor from relation OID */
rel = relation_open(relid, NoLock);
tupdesc = CreateTupleDescCopyConstr(rel->rd_att);
relation_close(rel, NoLock);
raw_attrs = initArrayResult(BYTEAOID, CurrentMemoryContext, false);
nattrs = tupdesc->natts;
if (nattrs < (t_infomask2 & HEAP_NATTS_MASK))
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("number of attributes in tuple header is greater than number of attributes in tuple descriptor")));
for (i = 0; i < nattrs; i++)
{
Form_pg_attribute attr;
bool is_null;
bytea *attr_data = NULL;
attr = TupleDescAttr(tupdesc, i);
is_null = (t_infomask & HEAP_HASNULL) && att_isnull(i, t_bits);
/*
* Tuple header can specify less attributes than tuple descriptor as
* ALTER TABLE ADD COLUMN without DEFAULT keyword does not actually
* change tuples in pages, so attributes with numbers greater than
* (t_infomask2 & HEAP_NATTS_MASK) should be treated as NULL.
*/
if (i >= (t_infomask2 & HEAP_NATTS_MASK))
is_null = true;
if (!is_null)
{
int len;
if (attr->attlen == -1)
{
off = att_align_pointer(off, attr->attalign, -1,
tupdata + off);
/*
* As VARSIZE_ANY throws an exception if it can't properly
* detect the type of external storage in macros VARTAG_SIZE,
* this check is repeated to have a nicer error handling.
*/
if (VARATT_IS_EXTERNAL(tupdata + off) &&
!VARATT_IS_EXTERNAL_ONDISK(tupdata + off) &&
!VARATT_IS_EXTERNAL_INDIRECT(tupdata + off))
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("first byte of varlena attribute is incorrect for attribute %d", i)));
len = VARSIZE_ANY(tupdata + off);
}
else
{
off = att_align_nominal(off, attr->attalign);
len = attr->attlen;
}
if (tupdata_len < off + len)
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("unexpected end of tuple data")));
if (attr->attlen == -1 && do_detoast)
attr_data = DatumGetByteaPCopy(tupdata + off);
else
{
attr_data = (bytea *) palloc(len + VARHDRSZ);
SET_VARSIZE(attr_data, len + VARHDRSZ);
memcpy(VARDATA(attr_data), tupdata + off, len);
}
off = att_addlength_pointer(off, attr->attlen,
tupdata + off);
}
raw_attrs = accumArrayResult(raw_attrs, PointerGetDatum(attr_data),
is_null, BYTEAOID, CurrentMemoryContext);
if (attr_data)
pfree(attr_data);
}
if (tupdata_len != off)
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("end of tuple reached without looking at all its data")));
return makeArrayResult(raw_attrs, CurrentMemoryContext);
}
/*
* tuple_data_split
*
* Split raw tuple data taken directly from page into distinct elements
* taking into account null values.
*/
PG_FUNCTION_INFO_V1(tuple_data_split);
Datum
tuple_data_split(PG_FUNCTION_ARGS)
{
Oid relid;
bytea *raw_data;
uint16 t_infomask;
uint16 t_infomask2;
char *t_bits_str;
bool do_detoast = false;
bits8 *t_bits = NULL;
Datum res;
relid = PG_GETARG_OID(0);
raw_data = PG_ARGISNULL(1) ? NULL : PG_GETARG_BYTEA_P(1);
t_infomask = PG_GETARG_INT16(2);
t_infomask2 = PG_GETARG_INT16(3);
t_bits_str = PG_ARGISNULL(4) ? NULL :
text_to_cstring(PG_GETARG_TEXT_PP(4));
if (PG_NARGS() >= 6)
do_detoast = PG_GETARG_BOOL(5);
if (!superuser())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("must be superuser to use raw page functions")));
if (!raw_data)
PG_RETURN_NULL();
/*
* Convert t_bits string back to the bits8 array as represented in the
* tuple header.
*/
if (t_infomask & HEAP_HASNULL)
{
int bits_str_len;
int bits_len;
bits_len = BITMAPLEN(t_infomask2 & HEAP_NATTS_MASK) * BITS_PER_BYTE;
if (!t_bits_str)
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("argument of t_bits is null, but it is expected to be null and %d character long",
bits_len)));
bits_str_len = strlen(t_bits_str);
if (bits_len != bits_str_len)
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("unexpected length of t_bits %u, expected %d",
bits_str_len, bits_len)));
/* do the conversion */
t_bits = text_to_bits(t_bits_str, bits_str_len);
}
else
{
if (t_bits_str)
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("t_bits string is expected to be NULL, but instead it is %zu bytes length",
strlen(t_bits_str))));
}
/* Split tuple data */
res = tuple_data_split_internal(relid, (char *) raw_data + VARHDRSZ,
VARSIZE(raw_data) - VARHDRSZ,
t_infomask, t_infomask2, t_bits,
do_detoast);
if (t_bits)
pfree(t_bits);
PG_RETURN_ARRAYTYPE_P(res);
}
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