Switch buffile.c/h to use pgoff_t instead of off_t

off_t was previously used for offsets, which is 4 bytes on Windows,
hence limiting the backend code to a hard limit for files longer than
2GB.  This leads to some simplification in these files, removing some
casts based on long, also 4 bytes on Windows.

This commit removes one comment introduced in db3c4c3a2d98, not relevant
anymore as pgoff_t is a safe 8-byte alternative on Windows.

This change is surprisingly not invasive, as the callers of
BufFileTell(), BufFileSeek() and BufFileTruncateFileSet() (worker.c,
tuplestore.c, etc.) track offsets in local structures that just to
switch from off_t to pgoff_t for the most part.

The file is still relying on a maximum file size of
MAX_PHYSICAL_FILESIZE (1GB).  This change allows the code to make this
maximum potentially larger in the future, or larger on a per-demand
basis.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/aUStrqoOCDRFAq1M@paquier.xyz

1 files changed, 11 insertions, 12 deletions

diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c
index 4e520065ae0..85b316d879d 100644
--- a/src/backend/storage/file/buffile.c
+++ b/src/backend/storage/file/buffile.c
@@ -92,7 +92,7 @@ struct BufFile
 	 * Position as seen by user of BufFile is (curFile, curOffset + pos).
 	 */
 	int			curFile;		/* file index (0..n) part of current pos */
-	off_t		curOffset;		/* offset part of current pos */
+	pgoff_t		curOffset;		/* offset part of current pos */
 	int			pos;			/* next read/write position in buffer */
 	int			nbytes;			/* total # of valid bytes in buffer */
 
@@ -503,7 +503,7 @@ BufFileDumpBuffer(BufFile *file)
 	 */
 	while (wpos < file->nbytes)
 	{
-		off_t		availbytes;
+		pgoff_t		availbytes;
 		instr_time	io_start;
 		instr_time	io_time;
 
@@ -524,7 +524,7 @@ BufFileDumpBuffer(BufFile *file)
 		bytestowrite = file->nbytes - wpos;
 		availbytes = MAX_PHYSICAL_FILESIZE - file->curOffset;
 
-		if ((off_t) bytestowrite > availbytes)
+		if ((pgoff_t) bytestowrite > availbytes)
 			bytestowrite = (int) availbytes;
 
 		thisfile = file->files[file->curFile];
@@ -729,7 +729,7 @@ BufFileFlush(BufFile *file)
  * BufFileSeek
  *
  * Like fseek(), except that target position needs two values in order to
- * work when logical filesize exceeds maximum value representable by off_t.
+ * work when logical filesize exceeds maximum value representable by pgoff_t.
  * We do not support relative seeks across more than that, however.
  * I/O errors are reported by ereport().
  *
@@ -737,10 +737,10 @@ BufFileFlush(BufFile *file)
  * impossible seek is attempted.
  */
 int
-BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
+BufFileSeek(BufFile *file, int fileno, pgoff_t offset, int whence)
 {
 	int			newFile;
-	off_t		newOffset;
+	pgoff_t		newOffset;
 
 	switch (whence)
 	{
@@ -754,8 +754,7 @@ BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
 
 			/*
 			 * Relative seek considers only the signed offset, ignoring
-			 * fileno. Note that large offsets (> 1 GB) risk overflow in this
-			 * add, unless we have 64-bit off_t.
+			 * fileno.
 			 */
 			newFile = file->curFile;
 			newOffset = (file->curOffset + file->pos) + offset;
@@ -830,7 +829,7 @@ BufFileSeek(BufFile *file, int fileno, off_t offset, int whence)
 }
 
 void
-BufFileTell(BufFile *file, int *fileno, off_t *offset)
+BufFileTell(BufFile *file, int *fileno, pgoff_t *offset)
 {
 	*fileno = file->curFile;
 	*offset = file->curOffset + file->pos;
@@ -852,7 +851,7 @@ BufFileSeekBlock(BufFile *file, int64 blknum)
 {
 	return BufFileSeek(file,
 					   (int) (blknum / BUFFILE_SEG_SIZE),
-					   (off_t) (blknum % BUFFILE_SEG_SIZE) * BLCKSZ,
+					   (pgoff_t) (blknum % BUFFILE_SEG_SIZE) * BLCKSZ,
 					   SEEK_SET);
 }
 
@@ -925,11 +924,11 @@ BufFileAppend(BufFile *target, BufFile *source)
  * and the offset.
  */
 void
-BufFileTruncateFileSet(BufFile *file, int fileno, off_t offset)
+BufFileTruncateFileSet(BufFile *file, int fileno, pgoff_t offset)
 {
 	int			numFiles = file->numFiles;
 	int			newFile = fileno;
-	off_t		newOffset = file->curOffset;
+	pgoff_t		newOffset = file->curOffset;
 	char		segment_name[MAXPGPATH];
 	int			i;