[PATCH] xfs_io: actually issue 0 size writes

[Eric Sandeen <sandeen@sandeen.net>]

While testing some stuff in generic_write_checks() in the
kernel I realized that you can't actually use xfs_io to send
a 0-byte write in.  This is actually a condition worth testing:

       If  count  is zero and fd refers to a regular file,
       then write() may return a failure status if one  of
       the  errors  below  is  detected.  If no errors are
       detected, 0 will be returned  without  causing  any
       other  effect.

So fix that up.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---

iff --git a/io/pwrite.c b/io/pwrite.c
index 54c3f78..26a7850 100644
--- a/io/pwrite.c
+++ b/io/pwrite.c
@@ -163,7 +163,7 @@ write_buffer(
 	int		ops = 0;
 
 	*total = 0;
-	while (count > 0) {
+	while (count >= 0) {
 		if (fd > 0) {	/* input file given, read buffer first */
 			if (read_buffer(fd, skip + *total, bs, &bar, 0, 1) < 0)
 				break;
@@ -182,6 +182,8 @@ write_buffer(
 			break;
 		offset += bytes;
 		count -= bytes;
+		if (count == 0)
+			break;
 	}
 	return ops;
 }

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