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Improve pg_dump's checkSeek() function to verify the functioning of ftello

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as well as fseeko, and to not assume that fseeko(fp, 0, SEEK_CUR) proves
anything.  Also improve some related comments.  Per my observation that
the SEEK_CUR test didn't actually work on some platforms, and subsequent
discussion with Robert Haas.

Back-patch to 8.4.  In earlier releases it's not that important whether
we get the hasSeek test right, but with parallel restore it matters.
This commit is contained in:
Tom Lane
2010-06-28 02:07:02 +00:00
parent b779ea8a9a
commit 04d9f4dab4
2 changed files with 44 additions and 23 deletions
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55
src/bin/pg_dump/pg_backup_archiver.c
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@ -15,7 +15,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_archiver.c,v 1.185 2010/05/15 21:41:16 tgl Exp $
* $PostgreSQL: pgsql/src/bin/pg_dump/pg_backup_archiver.c,v 1.186 2010/06/28 02:07:02 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1755,6 +1755,11 @@ _discoverArchiveFormat(ArchiveHandle *AH)
if (strncmp(sig, "PGDMP", 5) == 0)
{
/*
* Finish reading (most of) a custom-format header.
*
* NB: this code must agree with ReadHead().
*/
AH->vmaj = fgetc(fh);
AH->vmin = fgetc(fh);
@ -2981,7 +2986,12 @@ ReadHead(ArchiveHandle *AH)
int fmt;
struct tm crtm;
/* If we haven't already read the header... */
/*
* If we haven't already read the header, do so.
*
* NB: this code must agree with _discoverArchiveFormat(). Maybe find
* a way to unify the cases?
*/
if (!AH->readHeader)
{
if ((*AH->ReadBufPtr) (AH, tmpMag, 5) != 5)
@ -3000,7 +3010,6 @@ ReadHead(ArchiveHandle *AH)
AH->version = ((AH->vmaj * 256 + AH->vmin) * 256 + AH->vrev) * 256 + 0;
if (AH->version < K_VERS_1_0 || AH->version > K_VERS_MAX)
die_horribly(AH, modulename, "unsupported version (%d.%d) in file header\n",
AH->vmaj, AH->vmin);
@ -3068,27 +3077,37 @@ ReadHead(ArchiveHandle *AH)
/*
* checkSeek
* check to see if fseek can be performed.
* check to see if ftell/fseek can be performed.
*/
bool
checkSeek(FILE *fp)
{
if (fseeko(fp, 0, SEEK_CUR) != 0)
return false;
else if (sizeof(pgoff_t) > sizeof(long))
{
/*
* At this point, pgoff_t is too large for long, so we return based on
* whether an pgoff_t version of fseek is available.
*/
#ifdef HAVE_FSEEKO
return true;
#else
pgoff_t tpos;
/*
* If pgoff_t is wider than long, we must have "real" fseeko and not
* an emulation using fseek. Otherwise report no seek capability.
*/
#ifndef HAVE_FSEEKO
if (sizeof(pgoff_t) > sizeof(long))
return false;
#endif
}
else
return true;
/* Check that ftello works on this file */
errno = 0;
tpos = ftello(fp);
if (errno)
return false;
/*
* Check that fseeko(SEEK_SET) works, too. NB: we used to try to test
* this with fseeko(fp, 0, SEEK_CUR). But some platforms treat that as a
* successful no-op even on files that are otherwise unseekable.
*/
if (fseeko(fp, tpos, SEEK_SET) != 0)
return false;
return true;
}