[PATCH V2 1/2] tools/perf: Add utility function to read /proc/cpuinfo for any field

[Athira Rajeev <atrajeev@linux.vnet.ibm.com>]

/proc/cpuinfo provides information about type of processor, number
of CPU's etc. Reading /proc/cpuinfo file outputs useful information
by field name like cpu, platform, model (depending on architecture)
and its value separated by colon.

Add new utility function "cpuinfo_field" in "util/header.c" which
accepts field name as input string to search in /proc/cpuinfo content.
This returns the first matching value as resulting string. Example,
calling the function "cpuinfo_field(platform)" in powerpc returns
the platform value. This can be used to fetch processor information
from "cpuinfo" by other utilities/testcases.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
---
 tools/perf/util/header.c | 53 ++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/header.h |  1 +
 2 files changed, 54 insertions(+)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index a27132e5a5ef..f08857f96606 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -983,6 +983,59 @@ static int write_dir_format(struct feat_fd *ff,
 	return do_write(ff, &data->dir.version, sizeof(data->dir.version));
 }
 
+/*
+ * Return entry from /proc/cpuinfo
+ * indicated by "search" parameter.
+ */
+char *cpuinfo_field(const char *search)
+{
+	FILE *file;
+	char *buf = NULL;
+	char *copy_buf = NULL, *p;
+	size_t len = 0;
+
+	if (!search)
+		return NULL;
+
+	file = fopen("/proc/cpuinfo", "r");
+	if (!file)
+		return NULL;
+
+	while (getline(&buf, &len, file) > 0) {
+		if (!strncmp(buf, search, strlen(search)))
+			break;
+	}
+
+	if (feof(file))
+		goto done;
+
+	/*
+	 * Trim the new line and separate
+	 * value for search field from ":"
+	 * in cpuinfo line output.
+	 * Example output line:
+	 * platform : <value>
+	 */
+	copy_buf = buf;
+	p = strchr(copy_buf, ':');
+
+	/* Go to string after ":" */
+	copy_buf = p + 1;
+	p = strchr(copy_buf, '\n');
+	if (p)
+		*p = '\0';
+
+	/* Copy the filtered string after removing space to buf */
+	strcpy(buf, strim(copy_buf));
+
+	fclose(file);
+	return buf;
+
+done:
+	free(buf);
+	fclose(file);
+	return NULL;
+}
 /*
  * Check whether a CPU is online
  *
diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
index 0eb4bc29a5a4..b0f754364bd4 100644
--- a/tools/perf/util/header.h
+++ b/tools/perf/util/header.h
@@ -166,4 +166,5 @@ int get_cpuid(char *buffer, size_t sz);
 
 char *get_cpuid_str(struct perf_pmu *pmu __maybe_unused);
 int strcmp_cpuid_str(const char *s1, const char *s2);
+char *cpuinfo_field(const char *search);
 #endif /* __PERF_HEADER_H */
-- 
2.35.1