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Remove manual tracking of file position in pg_dump/pg_backup_custom.c. 

We do not really need to track the file position by hand.  We were
already relying on ftello() whenever the archive file is seekable,
while if it's not seekable we don't need the file position info
anyway because we're not going to be able to re-write the TOC.

Moreover, that tracking was buggy since it failed to account for
the effects of fseeko().  Somewhat remarkably, that seems not to
have made for any live bugs up to now.  We could fix the oversights,
but it seems better to just get rid of the whole error-prone mess.

In itself this is merely code cleanup.  However, it's necessary
infrastructure for an upcoming bug-fix patch (because that code
*does* need valid file position after fseeko).  The bug fix
needs to go back as far as v12; hence, back-patch that far.

Discussion: https://postgr.es/m/CALBH9DDuJ+scZc4MEvw5uO-=vRyR2=QF9+Yh=3hPEnKHWfS81A@mail.gmail.com
This commit is contained in:
Tom Lane 2020-07-17 12:14:28 -04:00
parent 49eb96852b
commit 447cf2f8e9
1 changed files with 14 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
src/bin/pg_dump/pg_backup_custom.c
View File

@ -70,14 +70,12 @@ typedef struct
{
CompressorState *cs;
int hasSeek;
pgoff_t filePos;
pgoff_t dataStart;
} lclContext;
typedef struct
{
int dataState;
pgoff_t dataPos;
pgoff_t dataPos; /* valid only if dataState=K_OFFSET_POS_SET */
} lclTocEntry;
@ -144,8 +142,6 @@ InitArchiveFmt_Custom(ArchiveHandle *AH)
AH->lo_buf_size = LOBBUFSIZE;
AH->lo_buf = (void *) pg_malloc(LOBBUFSIZE);
ctx->filePos = 0;
/*
* Now open the file
*/
@ -185,7 +181,6 @@ InitArchiveFmt_Custom(ArchiveHandle *AH)
ReadHead(AH);
ReadToc(AH);
ctx->dataStart = _getFilePos(AH, ctx);
}
}
@ -291,7 +286,8 @@ _StartData(ArchiveHandle *AH, TocEntry *te)
lclTocEntry *tctx = (lclTocEntry *) te->formatData;
tctx->dataPos = _getFilePos(AH, ctx);
tctx->dataState = K_OFFSET_POS_SET;
if (tctx->dataPos >= 0)
tctx->dataState = K_OFFSET_POS_SET;
_WriteByte(AH, BLK_DATA); /* Block type */
WriteInt(AH, te->dumpId); /* For sanity check */
@ -352,7 +348,8 @@ _StartBlobs(ArchiveHandle *AH, TocEntry *te)
lclTocEntry *tctx = (lclTocEntry *) te->formatData;
tctx->dataPos = _getFilePos(AH, ctx);
tctx->dataState = K_OFFSET_POS_SET;
if (tctx->dataPos >= 0)
tctx->dataState = K_OFFSET_POS_SET;
_WriteByte(AH, BLK_BLOBS); /* Block type */
WriteInt(AH, te->dumpId); /* For sanity check */
@ -553,7 +550,6 @@ _skipBlobs(ArchiveHandle *AH)
static void
_skipData(ArchiveHandle *AH)
{
lclContext *ctx = (lclContext *) AH->formatData;
size_t blkLen;
char *buf = NULL;
int buflen = 0;
@ -577,8 +573,6 @@ _skipData(ArchiveHandle *AH)
fatal("could not read from input file: %m");
}
ctx->filePos += blkLen;
blkLen = ReadInt(AH);
}
@ -596,12 +590,10 @@ _skipData(ArchiveHandle *AH)
static int
_WriteByte(ArchiveHandle *AH, const int i)
{
lclContext *ctx = (lclContext *) AH->formatData;
int res;
if ((res = fputc(i, AH->FH)) == EOF)
WRITE_ERROR_EXIT;
ctx->filePos += 1;
return 1;
}
@ -617,13 +609,11 @@ _WriteByte(ArchiveHandle *AH, const int i)
static int
_ReadByte(ArchiveHandle *AH)
{
lclContext *ctx = (lclContext *) AH->formatData;
int res;
res = getc(AH->FH);
if (res == EOF)
READ_ERROR_EXIT(AH->FH);
ctx->filePos += 1;
return res;
}
@ -637,11 +627,8 @@ _ReadByte(ArchiveHandle *AH)
static void
_WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
{
lclContext *ctx = (lclContext *) AH->formatData;
if (fwrite(buf, 1, len, AH->FH) != len)
WRITE_ERROR_EXIT;
ctx->filePos += len;
}
/*
@ -654,11 +641,8 @@ _WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
static void
_ReadBuf(ArchiveHandle *AH, void *buf, size_t len)
{
lclContext *ctx = (lclContext *) AH->formatData;
if (fread(buf, 1, len, AH->FH) != len)
READ_ERROR_EXIT(AH->FH);
ctx->filePos += len;
}
/*
@ -690,7 +674,6 @@ _CloseArchive(ArchiveHandle *AH)
if (tpos < 0 && ctx->hasSeek)
fatal("could not determine seek position in archive file: %m");
WriteToc(AH);
ctx->dataStart = _getFilePos(AH, ctx);
WriteDataChunks(AH, NULL);
/*
@ -864,30 +847,24 @@ _WorkerJobRestoreCustom(ArchiveHandle *AH, TocEntry *te)
/*
* Get the current position in the archive file.
*
* With a non-seekable archive file, we may not be able to obtain the
* file position. If so, just return -1. It's not too important in
* that case because we won't be able to rewrite the TOC to fill in
* data block offsets anyway.
*/
static pgoff_t
_getFilePos(ArchiveHandle *AH, lclContext *ctx)
{
pgoff_t pos;
if (ctx->hasSeek)
pos = ftello(AH->FH);
if (pos < 0)
{
/*
* Prior to 1.7 (pg7.3) we relied on the internally maintained
* pointer. Now we rely on ftello() always, unless the file has been
* found to not support it. For debugging purposes, print a warning
* if the internal pointer disagrees, so that we're more likely to
* notice if something's broken about the internal position tracking.
*/
pos = ftello(AH->FH);
if (pos < 0)
/* Not expected if we found we can seek. */
if (ctx->hasSeek)
fatal("could not determine seek position in archive file: %m");
if (pos != ctx->filePos)
pg_log_warning("ftell mismatch with expected position -- ftell used");
}
else
pos = ctx->filePos;
return pos;
}
@ -899,7 +876,6 @@ _getFilePos(ArchiveHandle *AH, lclContext *ctx)
static void
_readBlockHeader(ArchiveHandle *AH, int *type, int *id)
{
lclContext *ctx = (lclContext *) AH->formatData;
int byt;
/*
@ -920,7 +896,6 @@ _readBlockHeader(ArchiveHandle *AH, int *type, int *id)
*id = 0; /* don't return an uninitialized value */
return;
}
ctx->filePos += 1;
}
*id = ReadInt(AH);