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

diff --git a/src/bin/pg_dump/pg_backup_custom.c b/src/bin/pg_dump/pg_backup_custom.c
index 6ab122242ce3eb4b96f341928877fd2d4c23ea44..3a9881d6010cd2dedc6cd18e9c080f06e91f3d3b 100644 (file)
--- a/src/bin/pg_dump/pg_backup_custom.c
+++ b/src/bin/pg_dump/pg_backup_custom.c
@@ -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);
        }
 
 }
@@ -290,7 +285,8 @@ _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 */
@@ -350,7 +346,8 @@ _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 */
@@ -551,7 +548,6 @@ _skipBlobs(ArchiveHandle *AH)
 static void
 _skipData(ArchiveHandle *AH)
 {
-       lclContext *ctx = (lclContext *) AH->formatData;
        size_t          blkLen;
        char       *buf = NULL;
        int                     buflen = 0;
@@ -575,8 +571,6 @@ _skipData(ArchiveHandle *AH)
                                fatal("could not read from input file: %m");
                }
 
-               ctx->filePos += blkLen;
-
                blkLen = ReadInt(AH);
        }
 
@@ -594,12 +588,10 @@ _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;
 }
@@ -615,13 +607,11 @@ _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;
 }
 
@@ -635,11 +625,8 @@ _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;
 }
 
 /*
@@ -652,11 +639,8 @@ _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;
 }
 
 /*
@@ -688,7 +672,6 @@ _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);
 
                /*
@@ -862,30 +845,24 @@ _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;
 }
 
@@ -897,7 +874,6 @@ _getFilePos(ArchiveHandle *AH, lclContext *ctx)
 static void
 _readBlockHeader(ArchiveHandle *AH, int *type, int *id)
 {
-       lclContext *ctx = (lclContext *) AH->formatData;
        int                     byt;
 
        /*
@@ -918,7 +894,6 @@ _readBlockHeader(ArchiveHandle *AH, int *type, int *id)
                        *id = 0;                        /* don't return an uninitialized value */
                        return;
                }
-               ctx->filePos += 1;
        }
 
        *id = ReadInt(AH);