perf doc: Fix mmap failure checks in topdown example

[PATCH] perf doc: Fix mmap failure checks in topdown example

Posted by Hongfu Li 1 week, 5 days ago

Use MAP_FAILED instead of NULL to detect mmap errors, and fix the
slots_p variable name typo in the sample code.

Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
---
 tools/perf/Documentation/topdown.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Documentation/topdown.txt b/tools/perf/Documentation/topdown.txt
index 5c17fff694ee..fd4214f9a7b0 100644
--- a/tools/perf/Documentation/topdown.txt
+++ b/tools/perf/Documentation/topdown.txt
@@ -87,7 +87,7 @@ if (slots_fd < 0)
 
 /* Memory mapping the fd permits _rdpmc calls from userspace */
 void *slots_p = mmap(0, getpagesize(), PROT_READ, MAP_SHARED, slots_fd, 0);
-if (!slot_p)
+if (slots_p == MAP_FAILED)
 	.... error ...
 
 /*
@@ -107,7 +107,7 @@ if (metrics_fd < 0)
 
 /* Memory mapping the fd permits _rdpmc calls from userspace */
 void *metrics_p = mmap(0, getpagesize(), PROT_READ, MAP_SHARED, metrics_fd, 0);
-if (!metrics_p)
+if (metrics_p == MAP_FAILED)
 	... error ...
 
 Note: the file descriptors returned by the perf_event_open calls must be memory
-- 
2.25.1

Re: [PATCH] perf doc: Fix mmap failure checks in topdown example

Posted by Namhyung Kim 1 week, 3 days ago

On Mon, 13 Jul 2026 17:36:26 +0800, Hongfu Li wrote:
> Use MAP_FAILED instead of NULL to detect mmap errors, and fix the
> slots_p variable name typo in the sample code.
> 
> 
Applied to perf-tools-next, thanks!

Best regards,
Namhyung