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e293a5e816
The PMU information is in the kernel sysfs so it needs to scan the
directory to get the whole information like event aliases, formats and
so on. During the traversal, it opens a lot of files and directories
like below:
dir = opendir("/sys/bus/event_source/devices");
while (dentry = readdir(dir)) {
char buf[PATH_MAX];
snprintf(buf, sizeof(buf), "%s/%s",
"/sys/bus/event_source/devices", dentry->d_name);
fd = open(buf, O_RDONLY);
...
}
But this is not good since it needs to copy the string to build the
absolute pathname, and it makes redundant pathname walk (from the /sys)
unnecessarily. We can use openat(2) to open the file in the given
directory. While it's not a problem ususally, it can be a problem when
the kernel has contentions on the sysfs.
Add a couple of new helper to return the file descriptor of PMU
directory so that it can use it with relative paths.
* perf_pmu__event_source_devices_fd()
- returns a fd for the PMU root ("/sys/bus/event_source/devices")
* perf_pmu__pathname_fd()
- returns a fd for "<pmu>/<file>" under the PMU root
Now the above code can be converted something like below:
dirfd = perf_pmu__event_source_devices_fd();
dir = fdopendir(dirfd);
while (dentry = readdir(dir)) {
fd = openat(dirfd, dentry->d_name, O_RDONLY);
...
}
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230331202949.810326-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.