linux-kernel - [tip:perf/core] perf util: Add const modifier to buf in "writen" function

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Date:   Thu, 20 Jul 2017 01:59:27 -0700
From:   tip-bot for David Carrillo-Cisneros <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, linux-kernel@...r.kernel.org, sque@...omium.org,
        namhyung@...nel.org, acme@...hat.com, eranian@...gle.com,
        peterz@...radead.org, jolsa@...nel.org, wangnan0@...wei.com,
        dsahern@...il.com, ak@...ux.intel.com, tglx@...utronix.de,
        mingo@...nel.org, pjt@...gle.com, mhiramat@...nel.org,
        hekuang@...wei.com, alexander.shishkin@...ux.intel.com,
        davidcc@...gle.com
Subject: [tip:perf/core] perf util: Add const modifier to buf in "writen"
 function

Commit-ID:  7c72440506e2108494bab3b68a4118fa61a9dbf4
Gitweb:     http://git.kernel.org/tip/7c72440506e2108494bab3b68a4118fa61a9dbf4
Author:     David Carrillo-Cisneros <davidcc@...gle.com>
AuthorDate: Mon, 17 Jul 2017 21:25:37 -0700
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Tue, 18 Jul 2017 23:14:29 -0300

perf util: Add const modifier to buf in "writen" function

Make buf in helper function "writen" constant to simplify the life of
its callers.

This requires to hack a cast of buf prior to passing it to "ion" which
is simpler than the alternative of reworking the "ion" function to
provide a read and a write paths, the latter with constant buf argument.

Signed-off-by: David Carrillo-Cisneros <davidcc@...gle.com>
Acked-by: David Ahern <dsahern@...il.com>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: He Kuang <hekuang@...wei.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Paul Turner <pjt@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Simon Que <sque@...omium.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Wang Nan <wangnan0@...wei.com>
Link: http://lkml.kernel.org/r/20170718042549.145161-5-davidcc@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/util.c | 6 ++++--
 tools/perf/util/util.h | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index 9e4ea85..4c360da 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -281,6 +281,7 @@ static ssize_t ion(bool is_read, int fd, void *buf, size_t n)
 	size_t left = n;
 
 	while (left) {
+		/* buf must be treated as const if !is_read. */
 		ssize_t ret = is_read ? read(fd, buf, left) :
 					write(fd, buf, left);
 
@@ -308,9 +309,10 @@ ssize_t readn(int fd, void *buf, size_t n)
 /*
  * Write exactly 'n' bytes or return an error.
  */
-ssize_t writen(int fd, void *buf, size_t n)
+ssize_t writen(int fd, const void *buf, size_t n)
 {
-	return ion(false, fd, buf, n);
+	/* ion does not modify buf. */
+	return ion(false, fd, (void *)buf, n);
 }
 
 size_t hex_width(u64 v)
diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
index 062dd20..b136c27 100644
--- a/tools/perf/util/util.h
+++ b/tools/perf/util/util.h
@@ -38,7 +38,7 @@ int copyfile_ns(const char *from, const char *to, struct nsinfo *nsi);
 int copyfile_offset(int fromfd, loff_t from_ofs, int tofd, loff_t to_ofs, u64 size);
 
 ssize_t readn(int fd, void *buf, size_t n);
-ssize_t writen(int fd, void *buf, size_t n);
+ssize_t writen(int fd, const void *buf, size_t n);
 
 size_t hex_width(u64 v);
 int hex2u64(const char *ptr, u64 *val);