[PATCH] tools: usb: ffs-test: return the number of bytes written in pipe mode

[Sasha Levin <sashal@kernel.org>]

empty_out_buf() returns len, which the PAT_PIPE case never sets:

  ffs-test.c:551:7: warning: variable 'len' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]

Nothing sets pattern to PAT_PIPE, so the case is never reached and only
the warning is visible. Return nbytes once the buffer has been written
and flushed, and -1 if either fails.

Fixes: 93f2aa4ddd25c ("USB: ffs-test: FunctionFS testing program")
Assisted-by: LLM
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/usb/ffs-test.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/usb/ffs-test.c b/tools/usb/ffs-test.c
index f08060459b3f1..283db8979d67a 100644
--- a/tools/usb/ffs-test.c
+++ b/tools/usb/ffs-test.c
@@ -528,7 +528,6 @@ empty_out_buf(struct thread *ignore, const void *buf, size_t nbytes)
 {
 	const __u8 *p;
 	__u8 expected;
-	ssize_t ret;
 	size_t len;
 
 	(void)ignore;
@@ -550,9 +549,9 @@ empty_out_buf(struct thread *ignore, const void *buf, size_t nbytes)
 		break;
 
 	case PAT_PIPE:
-		ret = fwrite(buf, nbytes, 1, stdout);
-		if (ret > 0)
-			fflush(stdout);
+		if (fwrite(buf, nbytes, 1, stdout) != 1 || fflush(stdout))
+			return -1;
+		len = nbytes;
 		break;
 
 invalid:
-- 
2.53.0