linux-kernel - [PATCH 2/5] libperf: Add preadn()

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Date:   Fri, 20 May 2022 16:24:01 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] libperf: Add preadn()

Add preadn() to provide pread() and readn() semantics.

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/lib/perf/include/internal/lib.h |  2 ++
 tools/lib/perf/lib.c                  | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/tools/lib/perf/include/internal/lib.h b/tools/lib/perf/include/internal/lib.h
index 5175d491b2d4..85471a4b900f 100644
--- a/tools/lib/perf/include/internal/lib.h
+++ b/tools/lib/perf/include/internal/lib.h
@@ -9,4 +9,6 @@ extern unsigned int page_size;
 ssize_t readn(int fd, void *buf, size_t n);
 ssize_t writen(int fd, const void *buf, size_t n);
 
+ssize_t preadn(int fd, void *buf, size_t n, off_t offs);
+
 #endif /* __LIBPERF_INTERNAL_CPUMAP_H */
diff --git a/tools/lib/perf/lib.c b/tools/lib/perf/lib.c
index 18658931fc71..ecc8035a3ae3 100644
--- a/tools/lib/perf/lib.c
+++ b/tools/lib/perf/lib.c
@@ -38,6 +38,26 @@ ssize_t readn(int fd, void *buf, size_t n)
 	return ion(true, fd, buf, n);
 }
 
+ssize_t preadn(int fd, void *buf, size_t n, off_t offs)
+{
+	ssize_t ret;
+	off_t cur;
+
+	cur = lseek(fd, 0, SEEK_CUR);
+	if (cur < 0)
+		return -1;
+
+	if (lseek(fd, offs, SEEK_SET) < 0)
+		return -1;
+
+	ret = readn(fd, buf, n);
+
+	if (lseek(fd, cur, SEEK_CUR) < 0)
+		return -1;
+
+	return ret;
+}
+
 /*
  * Write exactly 'n' bytes or return an error.
  */
-- 
2.25.1