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perf doc: Fix mmap failure checks in topdown example

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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>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
This commit is contained in:
Hongfu Li 2026-07-13 17:36:26 +08:00 committed by Namhyung Kim
parent ea46211d7e
commit d30f2d869b
1 changed files with 2 additions and 2 deletions
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4
tools/perf/Documentation/topdown.txt
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@ -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