tools api: Add io__getline

Reads a line to allocated memory up to a newline following the getline
API.

Committer notes:

It also adds this new function to the 'api io' 'perf test' entry:

  $ perf test "api io"
   64: Test api io                                                     : Ok
  $

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tom Rix <trix@redhat.com>
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20230403184033.1836023-2-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/api/io.h

@@ -7,7 +7,9 @@
 #ifndef __API_IO__
 #define __API_IO__
 
+#include <errno.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 
 struct io {
@@ -112,4 +114,47 @@ static inline int io__get_dec(struct io *io, __u64 *dec)
 	}
 }
 
+/* Read up to and including the first newline following the pattern of getline. */
+static inline ssize_t io__getline(struct io *io, char **line_out, size_t *line_len_out)
+{
+	char buf[128];
+	int buf_pos = 0;
+	char *line = NULL, *temp;
+	size_t line_len = 0;
+	int ch = 0;
+
+	/* TODO: reuse previously allocated memory. */
+	free(*line_out);
+	while (ch != '\n') {
+		ch = io__get_char(io);
+
+		if (ch < 0)
+			break;
+
+		if (buf_pos == sizeof(buf)) {
+			temp = realloc(line, line_len + sizeof(buf));
+			if (!temp)
+				goto err_out;
+			line = temp;
+			memcpy(&line[line_len], buf, sizeof(buf));
+			line_len += sizeof(buf);
+			buf_pos = 0;
+		}
+		buf[buf_pos++] = (char)ch;
+	}
+	temp = realloc(line, line_len + buf_pos + 1);
+	if (!temp)
+		goto err_out;
+	line = temp;
+	memcpy(&line[line_len], buf, buf_pos);
+	line[line_len + buf_pos] = '\0';
+	line_len += buf_pos;
+	*line_out = line;
+	*line_len_out = line_len;
+	return line_len;
+err_out:
+	free(line);
+	return -ENOMEM;
+}
+
 #endif /* __API_IO__ */

tools/perf/tests/api-io.c

@@ -289,6 +289,40 @@ static int test_get_dec(void)
 	return ret;
 }
 
+static int test_get_line(void)
+{
+	char path[PATH_MAX];
+	struct io io;
+	char test_string[1024];
+	char *line = NULL;
+	size_t i, line_len = 0;
+	size_t buf_size = 128;
+	int ret = 0;
+
+	for (i = 0; i < 512; i++)
+		test_string[i] = 'a';
+	test_string[512] = '\n';
+	for (i = 513; i < 1023; i++)
+		test_string[i] = 'b';
+	test_string[1023] = '\0';
+
+	if (setup_test(path, test_string, buf_size, &io))
+		return -1;
+
+	EXPECT_EQUAL((int)io__getline(&io, &line, &line_len), 513);
+	EXPECT_EQUAL((int)strlen(line), 513);
+	for (i = 0; i < 512; i++)
+		EXPECT_EQUAL(line[i], 'a');
+	EXPECT_EQUAL(line[512], '\n');
+	EXPECT_EQUAL((int)io__getline(&io, &line, &line_len), 510);
+	for (i = 0; i < 510; i++)
+		EXPECT_EQUAL(line[i], 'b');
+
+	free(line);
+	cleanup_test(path, &io);
+	return ret;
+}
+
 static int test__api_io(struct test_suite *test __maybe_unused,
 			int subtest __maybe_unused)
 {
@@ -300,6 +334,8 @@ static int test__api_io(struct test_suite *test __maybe_unused,
 		ret = TEST_FAIL;
 	if (test_get_dec())
 		ret = TEST_FAIL;
+	if (test_get_line())
+		ret = TEST_FAIL;
 	return ret;
 }