[PATCHv3 3/7] perf tools: Fine tune readn function

[Jiri Olsa]

On Thu, Nov 28, 2013 at 08:19:51AM -0700, David Ahern wrote:
> On 11/28/13, 3:30 AM, Jiri Olsa wrote:
> >@@ -151,21 +152,26 @@ unsigned long convert_unit(unsigned long value, char *unit)
> >  	return value;
> >  }
> >
> >+/*
> >+ * Read exactly 'n' bytes or return an error.
> >+ */
> >  ssize_t readn(int fd, void *buf, size_t n)
> >  {
> >  	void *buf_start = buf;
> >+	size_t left = n;
> >
> >-	while (n) {
> >-		ssize_t ret = read(fd, buf, n);
> >+	while (left) {
> >+		ssize_t ret = read(fd, buf, left);
> >
> >  		if (ret <= 0)
> >  			return ret;
> 
> handle EINTR errors? no need to fail readn if the system call is
> interrupted.

right, how about the v3 below?

thanks,
jirka


---
Added a 'left' variable to make the flow clearer, and added a debug
check for the return value - returning 'n' is more obvious. Also do
not fail on EINTR error.

Added small comment for readn.

Original-patch-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/util.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index 9440481..f12eada 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -6,6 +6,8 @@
 #endif
 #include <stdio.h>
 #include <stdlib.h>
+#include <linux/kernel.h>
+#include <errno.h>
 
 /*
  * XXX We need to find a better place for these things...
@@ -151,21 +153,26 @@ unsigned long convert_unit(unsigned long value, char *unit)
 	return value;
 }
 
+/*
+ * Read exactly 'n' bytes or return an error.
+ */
 ssize_t readn(int fd, void *buf, size_t n)
 {
 	void *buf_start = buf;
+	size_t left = n;
 
-	while (n) {
-		ssize_t ret = read(fd, buf, n);
+	while (left) {
+		ssize_t ret = read(fd, buf, left);
 
-		if (ret <= 0)
+		if ((ret <= 0) && (errno != EINTR))
 			return ret;
 
-		n -= ret;
-		buf += ret;
+		left -= ret;
+		buf  += ret;
 	}
 
-	return buf - buf_start;
+	BUG_ON((size_t)(buf - buf_start) != n);
+	return n;
 }
 
 size_t hex_width(u64 v)
-- 
1.8.3.1

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