Tracefs location #710
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Tracefs location #710
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…ernel/debug/tracing. The default location for tracefs has been /sys/kernel/tracing since at least linux v4.1.
…uire elevated privileges if both /sys/kernel/tracing is readable and /proc/sys/kernel/perf_event_paranoid == -1
adamtassier
commented
Apr 16, 2025
src/recordhost.cpp
Outdated
| @@ -116,7 +116,7 @@ bool privsAlreadyElevated() | |||
| struct stat buf; | |||
| return stat(path, &buf) == 0 && ((buf.st_mode & 07777) & required) == required; | |||
| }; | |||
| static const auto paths = {"/sys/kernel/debug", "/sys/kernel/debug/tracing"}; | |||
| static const auto paths = {"/sys/kernel/", "/sys/kernel/tracing"}; | |||
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Checking /sys/kernel is probably redundant here right?
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I think so, yes - the old code was needed back then (Linux 3.x I think), because there tracing was mounted into debug, and thus needed to be checked separately
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that said, I wouldn't mind if we could rework this code:
check first if sys/kernel/tracing is usable, if so return early. otherwise keep backwards compat and check the two old locations?
milianw
requested changes
May 7, 2025
milianw
requested changes
May 8, 2025
milianw
reviewed
May 8, 2025
milianw
approved these changes
May 29, 2025
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Hi,
This PR changes the file system location that is checked for
tracefs. At least since linux v4.1 the default location has been/sys/kernel/tracing/instead of/sys/kernel/debug/tracing/(but the latter was kept for compatability).I also changed the tooltip of the 'off-cpu profiling' checkbox to better reflect the conditions under which it can be checked as I had to go look into the source code.
This was an issue for me when setting up rootless 'off-cpu profiling' (ie not using 'elevate privileges'). Turns out the problem was that
/sys/kernel/debug/tracing/was not readable on my machine but/sys/kernel/tracing/was (viatracinggroup).