tools api: Add simple timeout to io read

In situations like reading from a pipe it can be useful to have a
timeout so that the caller doesn't block indefinitely. Implement a
simple one based on poll.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yang Jihong <yangjihong1@huawei.com>
Link: http://lore.kernel.org/lkml/20230608061812.3715566-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/api/io.h

@@ -8,6 +8,7 @@
 #define __API_IO__
 
 #include <errno.h>
+#include <poll.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -23,6 +24,8 @@ struct io {
 	char *end;
 	/* Currently accessed data pointer. */
 	char *data;
+	/* Read timeout, 0 implies no timeout. */
+	int timeout_ms;
 	/* Set true on when the end of file on read error. */
 	bool eof;
 };
@@ -35,6 +38,7 @@ static inline void io__init(struct io *io, int fd,
 	io->buf = buf;
 	io->end = buf;
 	io->data = buf;
+	io->timeout_ms = 0;
 	io->eof = false;
 }
 
@@ -47,7 +51,29 @@ static inline int io__get_char(struct io *io)
 		return -1;
 
 	if (ptr == io->end) {
-		ssize_t n = read(io->fd, io->buf, io->buf_len);
+		ssize_t n;
+
+		if (io->timeout_ms != 0) {
+			struct pollfd pfds[] = {
+				{
+					.fd = io->fd,
+					.events = POLLIN,
+				},
+			};
+
+			n = poll(pfds, 1, io->timeout_ms);
+			if (n == 0)
+				errno = ETIMEDOUT;
+			if (n > 0 && !(pfds[0].revents & POLLIN)) {
+				errno = EIO;
+				n = -1;
+			}
+			if (n <= 0) {
+				io->eof = true;
+				return -1;
+			}
+		}
+		n = read(io->fd, io->buf, io->buf_len);
 
 		if (n <= 0) {
 			io->eof = true;