rawpage.c

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/*-------------------------------------------------------------------------
 *
 * rawpage.c
 *    Functions to extract a raw page as bytea and inspect it
 *
 * Access-method specific inspection functions are in separate files.
 *
 * Copyright (c) 2007-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    contrib/pageinspect/rawpage.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "access/relation.h"
#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "pageinspect.h"
#include "storage/bufmgr.h"
#include "storage/checksum.h"
#include "utils/builtins.h"
#include "utils/pg_lsn.h"
#include "utils/rel.h"
#include "utils/varlena.h"

PG_MODULE_MAGIC;

static bytea *get_raw_page_internal(text *relname, ForkNumber forknum,
                                    BlockNumber blkno);


/*
 * get_raw_page
 *
 * Returns a copy of a page from shared buffers as a bytea
 */
PG_FUNCTION_INFO_V1(get_raw_page);

Datum
get_raw_page(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    uint32      blkno = PG_GETARG_UINT32(1);
    bytea      *raw_page;

    /*
     * We don't normally bother to check the number of arguments to a C
     * function, but here it's needed for safety because early 8.4 beta
     * releases mistakenly redefined get_raw_page() as taking three arguments.
     */
    if (PG_NARGS() != 2)
        ereport(ERROR,
                (errmsg("wrong number of arguments to get_raw_page()"),
                 errhint("Run the updated pageinspect.sql script.")));

    raw_page = get_raw_page_internal(relname, MAIN_FORKNUM, blkno);

    PG_RETURN_BYTEA_P(raw_page);
}

/*
 * get_raw_page_fork
 *
 * Same, for any fork
 */
PG_FUNCTION_INFO_V1(get_raw_page_fork);

Datum
get_raw_page_fork(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    text       *forkname = PG_GETARG_TEXT_PP(1);
    uint32      blkno = PG_GETARG_UINT32(2);
    bytea      *raw_page;
    ForkNumber  forknum;

    forknum = forkname_to_number(text_to_cstring(forkname));

    raw_page = get_raw_page_internal(relname, forknum, blkno);

    PG_RETURN_BYTEA_P(raw_page);
}

/*
 * workhorse
 */
static bytea *
get_raw_page_internal(text *relname, ForkNumber forknum, BlockNumber blkno)
{
    bytea      *raw_page;
    RangeVar   *relrv;
    Relation    rel;
    char       *raw_page_data;
    Buffer      buf;

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

    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = relation_openrv(relrv, AccessShareLock);

    /* Check that this relation has storage */
    if (rel->rd_rel->relkind == RELKIND_VIEW)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot get raw page from view \"%s\"",
                        RelationGetRelationName(rel))));
    if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot get raw page from composite type \"%s\"",
                        RelationGetRelationName(rel))));
    if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot get raw page from foreign table \"%s\"",
                        RelationGetRelationName(rel))));
    if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot get raw page from partitioned table \"%s\"",
                        RelationGetRelationName(rel))));
    if (rel->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot get raw page from partitioned index \"%s\"",
                        RelationGetRelationName(rel))));

    /*
     * Reject attempts to read non-local temporary relations; we would be
     * likely to get wrong data since we have no visibility into the owning
     * session's local buffers.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot access temporary tables of other sessions")));

    if (blkno >= RelationGetNumberOfBlocksInFork(rel, forknum))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("block number %u is out of range for relation \"%s\"",
                        blkno, RelationGetRelationName(rel))));

    /* Initialize buffer to copy to */
    raw_page = (bytea *) palloc(BLCKSZ + VARHDRSZ);
    SET_VARSIZE(raw_page, BLCKSZ + VARHDRSZ);
    raw_page_data = VARDATA(raw_page);

    /* Take a verbatim copy of the page */

    buf = ReadBufferExtended(rel, forknum, blkno, RBM_NORMAL, NULL);
    LockBuffer(buf, BUFFER_LOCK_SHARE);

    memcpy(raw_page_data, BufferGetPage(buf), BLCKSZ);

    LockBuffer(buf, BUFFER_LOCK_UNLOCK);
    ReleaseBuffer(buf);

    relation_close(rel, AccessShareLock);

    return raw_page;
}


/*
 * get_page_from_raw
 *
 * Get a palloc'd, maxalign'ed page image from the result of get_raw_page()
 *
 * On machines with MAXALIGN = 8, the payload of a bytea is not maxaligned,
 * since it will start 4 bytes into a palloc'd value.  On alignment-picky
 * machines, this will cause failures in accesses to 8-byte-wide values
 * within the page.  We don't need to worry if accessing only 4-byte or
 * smaller fields, but when examining a struct that contains 8-byte fields,
 * use this function for safety.
 */
Page
get_page_from_raw(bytea *raw_page)
{
    Page        page;
    int         raw_page_size;

    raw_page_size = VARSIZE_ANY_EXHDR(raw_page);

    if (raw_page_size != BLCKSZ)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid page size"),
                 errdetail("Expected %d bytes, got %d.",
                           BLCKSZ, raw_page_size)));

    page = palloc(raw_page_size);

    memcpy(page, VARDATA_ANY(raw_page), raw_page_size);

    return page;
}


/*
 * page_header
 *
 * Allows inspection of page header fields of a raw page
 */

PG_FUNCTION_INFO_V1(page_header);

Datum
page_header(PG_FUNCTION_ARGS)
{
    bytea      *raw_page = PG_GETARG_BYTEA_P(0);
    int         raw_page_size;

    TupleDesc   tupdesc;

    Datum       result;
    HeapTuple   tuple;
    Datum       values[9];
    bool        nulls[9];

    PageHeader  page;
    XLogRecPtr  lsn;

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

    raw_page_size = VARSIZE(raw_page) - VARHDRSZ;

    /*
     * Check that enough data was supplied, so that we don't try to access
     * fields outside the supplied buffer.
     */
    if (raw_page_size < SizeOfPageHeaderData)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("input page too small (%d bytes)", raw_page_size)));

    page = (PageHeader) VARDATA(raw_page);

    /* 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");

    /* Extract information from the page header */

    lsn = PageGetLSN(page);

    /* pageinspect >= 1.2 uses pg_lsn instead of text for the LSN field. */
    if (TupleDescAttr(tupdesc, 0)->atttypid == TEXTOID)
    {
        char        lsnchar[64];

        snprintf(lsnchar, sizeof(lsnchar), "%X/%X",
                 (uint32) (lsn >> 32), (uint32) lsn);
        values[0] = CStringGetTextDatum(lsnchar);
    }
    else
        values[0] = LSNGetDatum(lsn);
    values[1] = UInt16GetDatum(page->pd_checksum);
    values[2] = UInt16GetDatum(page->pd_flags);
    values[3] = UInt16GetDatum(page->pd_lower);
    values[4] = UInt16GetDatum(page->pd_upper);
    values[5] = UInt16GetDatum(page->pd_special);
    values[6] = UInt16GetDatum(PageGetPageSize(page));
    values[7] = UInt16GetDatum(PageGetPageLayoutVersion(page));
    values[8] = TransactionIdGetDatum(page->pd_prune_xid);

    /* Build and return the tuple. */

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

    tuple = heap_form_tuple(tupdesc, values, nulls);
    result = HeapTupleGetDatum(tuple);

    PG_RETURN_DATUM(result);
}

/*
 * page_checksum
 *
 * Compute checksum of a raw page
 */

PG_FUNCTION_INFO_V1(page_checksum);

Datum
page_checksum(PG_FUNCTION_ARGS)
{
    bytea      *raw_page = PG_GETARG_BYTEA_P(0);
    uint32      blkno = PG_GETARG_INT32(1);
    int         raw_page_size;
    PageHeader  page;

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

    raw_page_size = VARSIZE(raw_page) - VARHDRSZ;

    /*
     * Check that the supplied page is of the right size.
     */
    if (raw_page_size != BLCKSZ)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("incorrect size of input page (%d bytes)", raw_page_size)));

    page = (PageHeader) VARDATA(raw_page);

    PG_RETURN_INT16(pg_checksum_page((char *) page, blkno));
}