Only call ftruncate() once, when the output file descriptor is closed at the end, instead of after every lseek() - this corrects the file growth on XFS but has the side effect that writing to stdout in >> (append) mode truncates the file to the wrong size (#45).

src/pv/state.c

@@ -257,6 +257,31 @@ void pv_freecontents_calc(pvtransfercalc_t calc)
 }
 
 
+/*
+ * Truncate the output file descriptor to its current position, if it's a
+ * valid fd, we're in sparse output mode, and no lseek() failed.
+ */
+static void pv_truncate_output(pvstate_t state)
+{
+	off_t current_offset;
+
+	if (!state->control.sparse_output)
+		return;
+	if (state->transfer.output_not_seekable)
+		return;
+	if (state->control.output_fd < 0)
+		return;
+
+	current_offset = lseek(state->control.output_fd, (off_t) 0, SEEK_CUR);
+	if (current_offset == (off_t) - 1)
+		return;
+
+	if (0 != ftruncate(state->control.output_fd, current_offset)) {
+		debug("%s: %s", "output ftruncate() failed", strerror(errno));
+	}
+}
+
+
 /*
  * Free a state structure, after which it can no longer be used.
  */
@@ -270,6 +295,7 @@ void pv_state_free(pvstate_t state)
 	 * still know the program name and output filename.
 	 */
 	if (state->control.output_fd >= 0) {
+		pv_truncate_output(state);
 		if (STDOUT_FILENO != state->control.output_fd) {
 			if (close(state->control.output_fd) < 0) {
 				pv_error("%s: %s",
@@ -631,6 +657,7 @@ void pv_state_output_set(pvstate_t state, int fd, const char *name)
 	 * Close any previous output file first, so we can report any errors
 	 * before we store the new output filename.
 	 */
+	pv_truncate_output(state);
 	if (state->control.output_fd >= 0 && state->control.output_fd != STDOUT_FILENO) {
 		if (close(state->control.output_fd) < 0) {
 			pv_error("%s: %s",

src/pv/transfer.c

@@ -709,22 +709,6 @@ static int pv__transfer_write(pvstate_t state, bool *eof_in, bool *eof_out, long
 				if (output_offset == (off_t) - 1) {
 					debug("%s: %s", "output lseek() failed", strerror(errno));
 					state->transfer.output_not_seekable = true;
-				} else if (0 != ftruncate(state->control.output_fd, output_offset)) {
-					/* TODO: don't ftruncate() immediately. */
-					/*
-					 * On XFS filesystems it looks like
-					 * this can actually make a sparse
-					 * file take up more space than a
-					 * regular file, though it's not
-					 * obvious yet whether the
-					 * ftruncate() is causing it or just
-					 * the lseek().
-					 *
-					 * Maybe just ftruncate() at the end
-					 * of the program.
-					 */
-					debug("%s: %s", "output ftruncate() failed", strerror(errno));
-					state->transfer.output_not_seekable = true;
 				} else {
 					/* Seek successful - skip write. */
 					nwritten = state->transfer.to_write;