[tip:perf/core] perf symbols: Convert lseek + read to pread

[tip-bot for Namhyung Kim]

Commit-ID:  c52686f9f888d23ca72f1309e86af8e91d075697
Gitweb:     http://git.kernel.org/tip/c52686f9f888d23ca72f1309e86af8e91d075697
Author:     Namhyung Kim <namhyung@xxxxxxxxxx>
AuthorDate: Thu, 29 Jan 2015 17:02:01 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Thu, 29 Jan 2015 17:02:01 -0300

perf symbols: Convert lseek + read to pread

When dso_cache__read() is called, it reads data from the given offset
using lseek + normal read syscall.  It can be combined to a single pread
syscall.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1422518843-25818-40-git-send-email-namhyung@xxxxxxxxxx
[ Fixed it up when cherry picking it from the multi threaded patchkit ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/dso.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 45be944..c2f7d3b 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -532,12 +532,8 @@ dso_cache__read(struct dso *dso, u64 offset, u8 *data, ssize_t size)
 			break;
 
 		cache_offset = offset & DSO__DATA_CACHE_MASK;
-		ret = -EINVAL;
 
-		if (-1 == lseek(dso->data.fd, cache_offset, SEEK_SET))
-			break;
-
-		ret = read(dso->data.fd, cache->data, DSO__DATA_CACHE_SIZE);
+		ret = pread(dso->data.fd, cache->data, DSO__DATA_CACHE_SIZE, cache_offset);
 		if (ret <= 0)
 			break;
 
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