Ensure write failure reports no-disk-space

A few places calling fwrite and gzwrite were not setting errno to ENOSPC
when reporting errors, as is customary; this led to some failures being
reported as
"could not write file: Success"
which makes us look silly.  Make a few of these places in pg_dump and
pg_basebackup use our customary pattern.

Backpatch-to: 9.5
Author: Justin Pryzby <pryzby@telsasoft.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20200611153753.GU14879@telsasoft.com

2 files changed, 30 insertions, 1 deletions

diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index dfd45aecc56..d472f4d1c23 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -892,8 +892,12 @@ writeTarData(
 #ifdef HAVE_LIBZ
 	if (ztarfile != NULL)
 	{
+		errno = 0;
 		if (gzwrite(ztarfile, buf, r) != r)
 		{
+			/* if write didn't set errno, assume problem is no disk space */
+			if (errno == 0)
+				errno = ENOSPC;
 			pg_log_error("could not write to compressed file \"%s\": %s",
 						 current_file, get_gz_error(ztarfile));
 			exit(1);
@@ -902,8 +906,12 @@ writeTarData(
 	else
 #endif
 	{
+		errno = 0;
 		if (fwrite(buf, r, 1, tarfile) != 1)
 		{
+			/* if write didn't set errno, assume problem is no disk space */
+			if (errno == 0)
+				errno = ENOSPC;
 			pg_log_error("could not write to file \"%s\": %m", current_file);
 			exit(1);
 		}
@@ -1596,8 +1604,12 @@ ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
 				continue;
 			}
 
+			errno = 0;
 			if (fwrite(copybuf, r, 1, file) != 1)
 			{
+				/* if write didn't set errno, assume problem is no disk space */
+				if (errno == 0)
+					errno = ENOSPC;
 				pg_log_error("could not write to file \"%s\": %m", filename);
 				exit(1);
 			}
diff --git a/src/bin/pg_dump/pg_backup_directory.c b/src/bin/pg_dump/pg_backup_directory.c
index dbe8b3836df..ffea0f7fd73 100644
--- a/src/bin/pg_dump/pg_backup_directory.c
+++ b/src/bin/pg_dump/pg_backup_directory.c
@@ -346,10 +346,15 @@ _WriteData(ArchiveHandle *AH, const void *data, size_t dLen)
 {
 	lclContext *ctx = (lclContext *) AH->formatData;
 
+	errno = 0;
 	if (dLen > 0 && cfwrite(data, dLen, ctx->dataFH) != dLen)
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
 		fatal("could not write to output file: %s",
 			  get_cfp_error(ctx->dataFH));
-
+	}
 
 	return;
 }
@@ -484,9 +489,15 @@ _WriteByte(ArchiveHandle *AH, const int i)
 	unsigned char c = (unsigned char) i;
 	lclContext *ctx = (lclContext *) AH->formatData;
 
+	errno = 0;
 	if (cfwrite(&c, 1, ctx->dataFH) != 1)
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
 		fatal("could not write to output file: %s",
 			  get_cfp_error(ctx->dataFH));
+	}
 
 	return 1;
 }
@@ -514,9 +525,15 @@ _WriteBuf(ArchiveHandle *AH, const void *buf, size_t len)
 {
 	lclContext *ctx = (lclContext *) AH->formatData;
 
+	errno = 0;
 	if (cfwrite(buf, len, ctx->dataFH) != len)
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
 		fatal("could not write to output file: %s",
 			  get_cfp_error(ctx->dataFH));
+	}
 
 	return;
 }