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.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
index d5e8cf0..9fc429d 100644 (file)
--- 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;