linux-kernel - [PATCH v1 1/2] tools api: Add simple timeout to io read

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Date:   Wed,  7 Jun 2023 23:18:11 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: [PATCH v1 1/2] 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@...gle.com>
---
 tools/lib/api/io.h | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
index d5e8cf0dada0..9fc429d2852d 100644
--- a/tools/lib/api/io.h
+++ b/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;
-- 
2.41.0.rc0.172.g3f132b7071-goog