be-fsstubs.c

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/*-------------------------------------------------------------------------
 *
 * be-fsstubs.c
 *    Builtin functions for open/close/read/write operations on large objects
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/libpq/be-fsstubs.c
 *
 * NOTES
 *    This should be moved to a more appropriate place.  It is here
 *    for lack of a better place.
 *
 *    These functions store LargeObjectDesc structs in a private MemoryContext,
 *    which means that large object descriptors hang around until we destroy
 *    the context at transaction end.  It'd be possible to prolong the lifetime
 *    of the context so that LO FDs are good across transactions (for example,
 *    we could release the context only if we see that no FDs remain open).
 *    But we'd need additional state in order to do the right thing at the
 *    end of an aborted transaction.  FDs opened during an aborted xact would
 *    still need to be closed, since they might not be pointing at valid
 *    relations at all.  Locking semantics are also an interesting problem
 *    if LOs stay open across transactions.  For now, we'll stick with the
 *    existing documented semantics of LO FDs: they're only good within a
 *    transaction.
 *
 *    As of PostgreSQL 8.0, much of the angst expressed above is no longer
 *    relevant, and in fact it'd be pretty easy to allow LO FDs to stay
 *    open across transactions.  (Snapshot relevancy would still be an issue.)
 *    However backwards compatibility suggests that we should stick to the
 *    status quo.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
 
#include "access/xact.h"
#include "catalog/pg_largeobject.h"
#include "libpq/be-fsstubs.h"
#include "libpq/libpq-fs.h"
#include "miscadmin.h"
#include "storage/fd.h"
#include "storage/large_object.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/snapmgr.h"
#include "varatt.h"
 
/* define this to enable debug logging */
/* #define FSDB 1 */
/* chunk size for lo_import/lo_export transfers */
#define BUFSIZE         8192
 
/*
 * LO "FD"s are indexes into the cookies array.
 *
 * A non-null entry is a pointer to a LargeObjectDesc allocated in the
 * LO private memory context "fscxt".  The cookies array itself is also
 * dynamically allocated in that context.  Its current allocated size is
 * cookies_size entries, of which any unused entries will be NULL.
 */
static LargeObjectDesc **cookies = NULL;
static int  cookies_size = 0;
 
static bool lo_cleanup_needed = false;
static MemoryContext fscxt = NULL;
 
static int  newLOfd(void);
static void closeLOfd(int fd);
static Oid  lo_import_internal(text *filename, Oid lobjOid);
 
 
/*****************************************************************************
 *  File Interfaces for Large Objects
 *****************************************************************************/
 
Datum
be_lo_open(PG_FUNCTION_ARGS)
{
    Oid         lobjId = PG_GETARG_OID(0);
    int32       mode = PG_GETARG_INT32(1);
    LargeObjectDesc *lobjDesc;
    int         fd;
 
#ifdef FSDB
    elog(DEBUG4, "lo_open(%u,%d)", lobjId, mode);
#endif
 
    if (mode & INV_WRITE)
        PreventCommandIfReadOnly("lo_open(INV_WRITE)");
 
    /*
     * Allocate a large object descriptor first.  This will also create
     * 'fscxt' if this is the first LO opened in this transaction.
     */
    fd = newLOfd();
 
    lobjDesc = inv_open(lobjId, mode, fscxt);
    lobjDesc->subid = GetCurrentSubTransactionId();
 
    /*
     * We must register the snapshot in TopTransaction's resowner so that it
     * stays alive until the LO is closed rather than until the current portal
     * shuts down.
     */
    if (lobjDesc->snapshot)
        lobjDesc->snapshot = RegisterSnapshotOnOwner(lobjDesc->snapshot,
                                                     TopTransactionResourceOwner);
 
    Assert(cookies[fd] == NULL);
    cookies[fd] = lobjDesc;
 
    PG_RETURN_INT32(fd);
}
 
Datum
be_lo_close(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
 
#ifdef FSDB
    elog(DEBUG4, "lo_close(%d)", fd);
#endif
 
    closeLOfd(fd);
 
    PG_RETURN_INT32(0);
}
 
 
/*****************************************************************************
 *  Bare Read/Write operations --- these are not fmgr-callable!
 *
 *  We assume the large object supports byte oriented reads and seeks so
 *  that our work is easier.
 *
 *****************************************************************************/
 
int
lo_read(int fd, char *buf, int len)
{
    int         status;
    LargeObjectDesc *lobj;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
    lobj = cookies[fd];
 
    /*
     * Check state.  inv_read() would throw an error anyway, but we want the
     * error to be about the FD's state not the underlying privilege; it might
     * be that the privilege exists but user forgot to ask for read mode.
     */
    if ((lobj->flags & IFS_RDLOCK) == 0)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("large object descriptor %d was not opened for reading",
                        fd)));
 
    status = inv_read(lobj, buf, len);
 
    return status;
}
 
int
lo_write(int fd, const char *buf, int len)
{
    int         status;
    LargeObjectDesc *lobj;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
    lobj = cookies[fd];
 
    /* see comment in lo_read() */
    if ((lobj->flags & IFS_WRLOCK) == 0)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("large object descriptor %d was not opened for writing",
                        fd)));
 
    status = inv_write(lobj, buf, len);
 
    return status;
}
 
Datum
be_lo_lseek(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int32       offset = PG_GETARG_INT32(1);
    int32       whence = PG_GETARG_INT32(2);
    int64       status;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
 
    status = inv_seek(cookies[fd], offset, whence);
 
    /* guard against result overflow */
    if (status != (int32) status)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("lo_lseek result out of range for large-object descriptor %d",
                        fd)));
 
    PG_RETURN_INT32((int32) status);
}
 
Datum
be_lo_lseek64(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int64       offset = PG_GETARG_INT64(1);
    int32       whence = PG_GETARG_INT32(2);
    int64       status;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
 
    status = inv_seek(cookies[fd], offset, whence);
 
    PG_RETURN_INT64(status);
}
 
Datum
be_lo_creat(PG_FUNCTION_ARGS)
{
    Oid         lobjId;
 
    PreventCommandIfReadOnly("lo_creat()");
 
    lo_cleanup_needed = true;
    lobjId = inv_create(InvalidOid);
 
    PG_RETURN_OID(lobjId);
}
 
Datum
be_lo_create(PG_FUNCTION_ARGS)
{
    Oid         lobjId = PG_GETARG_OID(0);
 
    PreventCommandIfReadOnly("lo_create()");
 
    lo_cleanup_needed = true;
    lobjId = inv_create(lobjId);
 
    PG_RETURN_OID(lobjId);
}
 
Datum
be_lo_tell(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int64       offset;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
 
    offset = inv_tell(cookies[fd]);
 
    /* guard against result overflow */
    if (offset != (int32) offset)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("lo_tell result out of range for large-object descriptor %d",
                        fd)));
 
    PG_RETURN_INT32((int32) offset);
}
 
Datum
be_lo_tell64(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int64       offset;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
 
    offset = inv_tell(cookies[fd]);
 
    PG_RETURN_INT64(offset);
}
 
Datum
be_lo_unlink(PG_FUNCTION_ARGS)
{
    Oid         lobjId = PG_GETARG_OID(0);
 
    PreventCommandIfReadOnly("lo_unlink()");
 
    if (!LargeObjectExists(lobjId))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("large object %u does not exist", lobjId)));
 
    /*
     * Must be owner of the large object.  It would be cleaner to check this
     * in inv_drop(), but we want to throw the error before not after closing
     * relevant FDs.
     */
    if (!lo_compat_privileges &&
        !object_ownercheck(LargeObjectRelationId, lobjId, GetUserId()))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be owner of large object %u", lobjId)));
 
    /*
     * If there are any open LO FDs referencing that ID, close 'em.
     */
    if (fscxt != NULL)
    {
        int         i;
 
        for (i = 0; i < cookies_size; i++)
        {
            if (cookies[i] != NULL && cookies[i]->id == lobjId)
                closeLOfd(i);
        }
    }
 
    /*
     * inv_drop does not create a need for end-of-transaction cleanup and
     * hence we don't need to set lo_cleanup_needed.
     */
    PG_RETURN_INT32(inv_drop(lobjId));
}
 
/*****************************************************************************
 *  Read/Write using bytea
 *****************************************************************************/
 
Datum
be_loread(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int32       len = PG_GETARG_INT32(1);
    bytea      *retval;
    int         totalread;
 
    if (len < 0)
        len = 0;
 
    retval = (bytea *) palloc(VARHDRSZ + len);
    totalread = lo_read(fd, VARDATA(retval), len);
    SET_VARSIZE(retval, totalread + VARHDRSZ);
 
    PG_RETURN_BYTEA_P(retval);
}
 
Datum
be_lowrite(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    bytea      *wbuf = PG_GETARG_BYTEA_PP(1);
    int         bytestowrite;
    int         totalwritten;
 
    PreventCommandIfReadOnly("lowrite()");
 
    bytestowrite = VARSIZE_ANY_EXHDR(wbuf);
    totalwritten = lo_write(fd, VARDATA_ANY(wbuf), bytestowrite);
    PG_RETURN_INT32(totalwritten);
}
 
/*****************************************************************************
 *   Import/Export of Large Object
 *****************************************************************************/
 
/*
 * lo_import -
 *    imports a file as an (inversion) large object.
 */
Datum
be_lo_import(PG_FUNCTION_ARGS)
{
    text       *filename = PG_GETARG_TEXT_PP(0);
 
    PG_RETURN_OID(lo_import_internal(filename, InvalidOid));
}
 
/*
 * lo_import_with_oid -
 *    imports a file as an (inversion) large object specifying oid.
 */
Datum
be_lo_import_with_oid(PG_FUNCTION_ARGS)
{
    text       *filename = PG_GETARG_TEXT_PP(0);
    Oid         oid = PG_GETARG_OID(1);
 
    PG_RETURN_OID(lo_import_internal(filename, oid));
}
 
static Oid
lo_import_internal(text *filename, Oid lobjOid)
{
    int         fd;
    int         nbytes,
                tmp PG_USED_FOR_ASSERTS_ONLY;
    char        buf[BUFSIZE];
    char        fnamebuf[MAXPGPATH];
    LargeObjectDesc *lobj;
    Oid         oid;
 
    PreventCommandIfReadOnly("lo_import()");
 
    /*
     * open the file to be read in
     */
    text_to_cstring_buffer(filename, fnamebuf, sizeof(fnamebuf));
    fd = OpenTransientFile(fnamebuf, O_RDONLY | PG_BINARY);
    if (fd < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open server file \"%s\": %m",
                        fnamebuf)));
 
    /*
     * create an inversion object
     */
    lo_cleanup_needed = true;
    oid = inv_create(lobjOid);
 
    /*
     * read in from the filesystem and write to the inversion object
     */
    lobj = inv_open(oid, INV_WRITE, CurrentMemoryContext);
 
    while ((nbytes = read(fd, buf, BUFSIZE)) > 0)
    {
        tmp = inv_write(lobj, buf, nbytes);
        Assert(tmp == nbytes);
    }
 
    if (nbytes < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not read server file \"%s\": %m",
                        fnamebuf)));
 
    inv_close(lobj);
 
    if (CloseTransientFile(fd) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m",
                        fnamebuf)));
 
    return oid;
}
 
/*
 * lo_export -
 *    exports an (inversion) large object.
 */
Datum
be_lo_export(PG_FUNCTION_ARGS)
{
    Oid         lobjId = PG_GETARG_OID(0);
    text       *filename = PG_GETARG_TEXT_PP(1);
    int         fd;
    int         nbytes,
                tmp;
    char        buf[BUFSIZE];
    char        fnamebuf[MAXPGPATH];
    LargeObjectDesc *lobj;
    mode_t      oumask;
 
    /*
     * open the inversion object (no need to test for failure)
     */
    lo_cleanup_needed = true;
    lobj = inv_open(lobjId, INV_READ, CurrentMemoryContext);
 
    /*
     * open the file to be written to
     *
     * Note: we reduce backend's normal 077 umask to the slightly friendlier
     * 022. This code used to drop it all the way to 0, but creating
     * world-writable export files doesn't seem wise.
     */
    text_to_cstring_buffer(filename, fnamebuf, sizeof(fnamebuf));
    oumask = umask(S_IWGRP | S_IWOTH);
    PG_TRY();
    {
        fd = OpenTransientFilePerm(fnamebuf, O_CREAT | O_WRONLY | O_TRUNC | PG_BINARY,
                                   S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
    }
    PG_FINALLY();
    {
        umask(oumask);
    }
    PG_END_TRY();
    if (fd < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not create server file \"%s\": %m",
                        fnamebuf)));
 
    /*
     * read in from the inversion file and write to the filesystem
     */
    while ((nbytes = inv_read(lobj, buf, BUFSIZE)) > 0)
    {
        tmp = write(fd, buf, nbytes);
        if (tmp != nbytes)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not write server file \"%s\": %m",
                            fnamebuf)));
    }
 
    if (CloseTransientFile(fd) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m",
                        fnamebuf)));
 
    inv_close(lobj);
 
    PG_RETURN_INT32(1);
}
 
/*
 * lo_truncate -
 *    truncate a large object to a specified length
 */
static void
lo_truncate_internal(int32 fd, int64 len)
{
    LargeObjectDesc *lobj;
 
    if (fd < 0 || fd >= cookies_size || cookies[fd] == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("invalid large-object descriptor: %d", fd)));
    lobj = cookies[fd];
 
    /* see comment in lo_read() */
    if ((lobj->flags & IFS_WRLOCK) == 0)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("large object descriptor %d was not opened for writing",
                        fd)));
 
    inv_truncate(lobj, len);
}
 
Datum
be_lo_truncate(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int32       len = PG_GETARG_INT32(1);
 
    PreventCommandIfReadOnly("lo_truncate()");
 
    lo_truncate_internal(fd, len);
    PG_RETURN_INT32(0);
}
 
Datum
be_lo_truncate64(PG_FUNCTION_ARGS)
{
    int32       fd = PG_GETARG_INT32(0);
    int64       len = PG_GETARG_INT64(1);
 
    PreventCommandIfReadOnly("lo_truncate64()");
 
    lo_truncate_internal(fd, len);
    PG_RETURN_INT32(0);
}
 
/*
 * AtEOXact_LargeObject -
 *       prepares large objects for transaction commit
 */
void
AtEOXact_LargeObject(bool isCommit)
{
    int         i;
 
    if (!lo_cleanup_needed)
        return;                 /* no LO operations in this xact */
 
    /*
     * Close LO fds and clear cookies array so that LO fds are no longer good.
     * The memory context and resource owner holding them are going away at
     * the end-of-transaction anyway, but on commit, we need to close them to
     * avoid warnings about leaked resources at commit.  On abort we can skip
     * this step.
     */
    if (isCommit)
    {
        for (i = 0; i < cookies_size; i++)
        {
            if (cookies[i] != NULL)
                closeLOfd(i);
        }
    }
 
    /* Needn't actually pfree since we're about to zap context */
    cookies = NULL;
    cookies_size = 0;
 
    /* Release the LO memory context to prevent permanent memory leaks. */
    if (fscxt)
        MemoryContextDelete(fscxt);
    fscxt = NULL;
 
    /* Give inv_api.c a chance to clean up, too */
    close_lo_relation(isCommit);
 
    lo_cleanup_needed = false;
}
 
/*
 * AtEOSubXact_LargeObject
 *      Take care of large objects at subtransaction commit/abort
 *
 * Reassign LOs created/opened during a committing subtransaction
 * to the parent subtransaction.  On abort, just close them.
 */
void
AtEOSubXact_LargeObject(bool isCommit, SubTransactionId mySubid,
                        SubTransactionId parentSubid)
{
    int         i;
 
    if (fscxt == NULL)          /* no LO operations in this xact */
        return;
 
    for (i = 0; i < cookies_size; i++)
    {
        LargeObjectDesc *lo = cookies[i];
 
        if (lo != NULL && lo->subid == mySubid)
        {
            if (isCommit)
                lo->subid = parentSubid;
            else
                closeLOfd(i);
        }
    }
}
 
/*****************************************************************************
 *  Support routines for this file
 *****************************************************************************/
 
static int
newLOfd(void)
{
    int         i,
                newsize;
 
    lo_cleanup_needed = true;
    if (fscxt == NULL)
        fscxt = AllocSetContextCreate(TopMemoryContext,
                                      "Filesystem",
                                      ALLOCSET_DEFAULT_SIZES);
 
    /* Try to find a free slot */
    for (i = 0; i < cookies_size; i++)
    {
        if (cookies[i] == NULL)
            return i;
    }
 
    /* No free slot, so make the array bigger */
    if (cookies_size <= 0)
    {
        /* First time through, arbitrarily make 64-element array */
        i = 0;
        newsize = 64;
        cookies = (LargeObjectDesc **)
            MemoryContextAllocZero(fscxt, newsize * sizeof(LargeObjectDesc *));
    }
    else
    {
        /* Double size of array */
        i = cookies_size;
        newsize = cookies_size * 2;
        cookies =
            repalloc0_array(cookies, LargeObjectDesc *, cookies_size, newsize);
    }
    cookies_size = newsize;
 
    return i;
}
 
static void
closeLOfd(int fd)
{
    LargeObjectDesc *lobj;
 
    /*
     * Make sure we do not try to free twice if this errors out for some
     * reason.  Better a leak than a crash.
     */
    lobj = cookies[fd];
    cookies[fd] = NULL;
 
    if (lobj->snapshot)
        UnregisterSnapshotFromOwner(lobj->snapshot,
                                    TopTransactionResourceOwner);
    inv_close(lobj);
}
 
/*****************************************************************************
 *  Wrappers oriented toward SQL callers
 *****************************************************************************/
 
/*
 * Read [offset, offset+nbytes) within LO; when nbytes is -1, read to end.
 */
static bytea *
lo_get_fragment_internal(Oid loOid, int64 offset, int32 nbytes)
{
    LargeObjectDesc *loDesc;
    int64       loSize;
    int64       result_length;
    int         total_read PG_USED_FOR_ASSERTS_ONLY;
    bytea      *result = NULL;
 
    lo_cleanup_needed = true;
    loDesc = inv_open(loOid, INV_READ, CurrentMemoryContext);
 
    /*
     * Compute number of bytes we'll actually read, accommodating nbytes == -1
     * and reads beyond the end of the LO.
     */
    loSize = inv_seek(loDesc, 0, SEEK_END);
    if (loSize > offset)
    {
        if (nbytes >= 0 && nbytes <= loSize - offset)
            result_length = nbytes; /* request is wholly inside LO */
        else
            result_length = loSize - offset;    /* adjust to end of LO */
    }
    else
        result_length = 0;      /* request is wholly outside LO */
 
    /*
     * A result_length calculated from loSize may not fit in a size_t.  Check
     * that the size will satisfy this and subsequently-enforced size limits.
     */
    if (result_length > MaxAllocSize - VARHDRSZ)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("large object read request is too large")));
 
    result = (bytea *) palloc(VARHDRSZ + result_length);
 
    inv_seek(loDesc, offset, SEEK_SET);
    total_read = inv_read(loDesc, VARDATA(result), result_length);
    Assert(total_read == result_length);
    SET_VARSIZE(result, result_length + VARHDRSZ);
 
    inv_close(loDesc);
 
    return result;
}
 
/*
 * Read entire LO
 */
Datum
be_lo_get(PG_FUNCTION_ARGS)
{
    Oid         loOid = PG_GETARG_OID(0);
    bytea      *result;
 
    result = lo_get_fragment_internal(loOid, 0, -1);
 
    PG_RETURN_BYTEA_P(result);
}
 
/*
 * Read range within LO
 */
Datum
be_lo_get_fragment(PG_FUNCTION_ARGS)
{
    Oid         loOid = PG_GETARG_OID(0);
    int64       offset = PG_GETARG_INT64(1);
    int32       nbytes = PG_GETARG_INT32(2);
    bytea      *result;
 
    if (nbytes < 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("requested length cannot be negative")));
 
    result = lo_get_fragment_internal(loOid, offset, nbytes);
 
    PG_RETURN_BYTEA_P(result);
}
 
/*
 * Create LO with initial contents given by a bytea argument
 */
Datum
be_lo_from_bytea(PG_FUNCTION_ARGS)
{
    Oid         loOid = PG_GETARG_OID(0);
    bytea      *str = PG_GETARG_BYTEA_PP(1);
    LargeObjectDesc *loDesc;
    int         written PG_USED_FOR_ASSERTS_ONLY;
 
    PreventCommandIfReadOnly("lo_from_bytea()");
 
    lo_cleanup_needed = true;
    loOid = inv_create(loOid);
    loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
    written = inv_write(loDesc, VARDATA_ANY(str), VARSIZE_ANY_EXHDR(str));
    Assert(written == VARSIZE_ANY_EXHDR(str));
    inv_close(loDesc);
 
    PG_RETURN_OID(loOid);
}
 
/*
 * Update range within LO
 */
Datum
be_lo_put(PG_FUNCTION_ARGS)
{
    Oid         loOid = PG_GETARG_OID(0);
    int64       offset = PG_GETARG_INT64(1);
    bytea      *str = PG_GETARG_BYTEA_PP(2);
    LargeObjectDesc *loDesc;
    int         written PG_USED_FOR_ASSERTS_ONLY;
 
    PreventCommandIfReadOnly("lo_put()");
 
    lo_cleanup_needed = true;
    loDesc = inv_open(loOid, INV_WRITE, CurrentMemoryContext);
    inv_seek(loDesc, offset, SEEK_SET);
    written = inv_write(loDesc, VARDATA_ANY(str), VARSIZE_ANY_EXHDR(str));
    Assert(written == VARSIZE_ANY_EXHDR(str));
    inv_close(loDesc);
 
    PG_RETURN_VOID();
}