[PATCH] generic/286: fix integer underflow on block sizes != 4096

[Jakob Unterwurzacher <jakobunt@gmail.com>]

The read loop always requested 4096 bytes, which only works
when the total read length is a multiple of 4096 bytes.

This is not neccessarily true, and when it's not, len wraps
around to UINT64_MAX and you get a lot of these:

	ERROR: [error:38] reached EOF:Success

This was caught when running xfstests against gocryptfs,
an encrypted overlay file system.

On ext4, the test still passes after this change.

Signed-off-by: Jakob Unterwurzacher <jakobunt@gmail.com>
---
 src/seek_copy_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/seek_copy_test.c b/src/seek_copy_test.c
index 0c2c6a3d..28c021e2 100644
--- a/src/seek_copy_test.c
+++ b/src/seek_copy_test.c
@@ -98,7 +98,7 @@ do_extent_copy(int src_fd, int dest_fd, off_t data_off, off_t hole_off)
 	}
 
 	while (len > 0) {
-		ssize_t nr_read = read(src_fd, buf, BUF_SIZE);
+		ssize_t nr_read = read(src_fd, buf, MIN(len, BUF_SIZE));
 		if (nr_read < 0) {
 			if (errno == EINTR)
 				continue;
-- 
2.31.1