[PATCH 3/5] xfs_copy: distinguish short writes to EOD from runtime errors

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Detect short writes to the end of the destination device and report
them.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 copy/xfs_copy.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)


diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 79f65946..d9a14a95 100644
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -889,18 +889,28 @@ main(int argc, char **argv)
 		} else  {
 			char	*lb[XFS_MAX_SECTORSIZE] = { NULL };
 			off64_t	off;
+			ssize_t	len;
 
 			/* ensure device files are sufficiently large */
 
 			off = mp->m_sb.sb_dblocks * source_blocksize;
 			off -= sizeof(lb);
-			if (pwrite(target[i].fd, lb, sizeof(lb), off) < 0)  {
+			len = pwrite(target[i].fd, lb, XFS_MAX_SECTORSIZE, off);
+			if (len < 0) {
 				do_log(_("%s:  failed to write last block\n"),
 					progname);
 				do_log(_("\tIs target \"%s\" too small?\n"),
 					target[i].name);
 				die_perror();
 			}
+			if (len != XFS_MAX_SECTORSIZE) {
+				do_log(
+ _("%s:  short write to last block: %zd bytes, %zu expected\n"),
+					progname, len, XFS_MAX_SECTORSIZE);
+				do_log(_("\tIs target \"%s\" too small?\n"),
+					target[i].name);
+				exit(1);
+			}
 		}
 	}