[PATCH] tools: gpio: gpio-watch: do not clobber errno on read error

[Gu Bin]

gpio-watch reads line change events from a gpiochip character device
and reports a read() error or short read with perror(), which prints
strerror(errno).  If read() fails, say with EINTR, the inner

	if (rd != sizeof(chg))
		errno = EIO;

replaces the real errno with EIO, so the message always reports
"Input/output error" instead of the actual cause.

Only synthesize EIO for short reads (rd >= 0), keeping the errno
that read() set when it failed.

Fixes: 33f0c47b8fb4 ("tools: gpio: implement gpio-watch")
Signed-off-by: Gu Bin <gubin@xxxxxxxxxxxxxxxxxxxx>
---
 tools/gpio/gpio-watch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/gpio/gpio-watch.c b/tools/gpio/gpio-watch.c
index 41e76d2441922..e7733cedcf0d6 100644
--- a/tools/gpio/gpio-watch.c
+++ b/tools/gpio/gpio-watch.c
@@ -64,7 +64,7 @@ int main(int argc, char **argv)
 			memset(&chg, 0, sizeof(chg));
 			rd = read(pfd.fd, &chg, sizeof(chg));
 			if (rd < 0 || rd != sizeof(chg)) {
-				if (rd != sizeof(chg))
+				if (rd >= 0 && rd != sizeof(chg))
 					errno = EIO;
 
 				perror("error reading line change event");
-- 
2.50.1.windows.1