Em Tue, Aug 04, 2015 at 04:44:53PM +0200, Milian Wolff escreveu:
> on ArchLinux with Linux 4.1.3, perf 4.1.0, I get:
>
> $ perf trace
> Error: No permissions to read
> /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
> Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'
> $ sudo mount -o remount,mode=755 /sys/kernel/debug
> $ perf trace
> Error: No permissions to read
> /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
> Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'
>
> This is b/c Arch uses tracefs, and running
>
> $ sudo mount -o remount,mode=755 /sys/kernel/debug/tracefs
>
> fixes the issue for me. Could someone please amend the error message? Do I
> also need to remount debugfs, or is tracefs sufficient for using more
> advanced
> perf tools?
Well:
[acme@zoo linux]$ perf trace ls
Error: No permissions to read
/sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'
[acme@zoo linux]$ ls -la /sys/kernel/debug
ls: cannot open directory /sys/kernel/debug: Permission denied
[acme@zoo linux]$
So, I can't access debugfs, that is where the canonical mount point for
tracefs is, so the message can be read as well as: "hey, let me get to
where tracefs is".
Once that is done:
[acme@zoo linux]$ sudo mount -o remount,mode=755 /sys/kernel/debug
[sudo] password for acme:
[acme@zoo linux]$ ls -la /sys/kernel/debug
total 0
drwxr-xr-x. 32 root root 0 Aug 4 08:35 .
drwxr-xr-x. 10 root root 0 Aug 4 08:35 ..
drwxr-xr-x. 2 root root 0 Aug 4 08:35 acpi
<SNIP>
drwxr-xr-x. 2 root root 0 Aug 4 08:35 zswap
[acme@zoo linux]$ ls -la /sys/kernel/debug/tracing/
ls: cannot open directory /sys/kernel/debug/tracing/: Permission denied
[acme@zoo linux]$
So, if I try:
[acme@zoo linux]$ trace usleep 1
Error: No permissions to read
/sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'
[acme@zoo linux]$
It asks for that same remount to be done, this time for tracefs, once
that is done:
[acme@zoo linux]$ sudo mount -o remount,mode=755 /sys/kernel/debug/tracing
[acme@zoo linux]$ trace usleep 1
0.086 (0.001 ms): usleep/10122 brk(
) = 0x556309717000
0.101 (0.003 ms): usleep/10122 mmap(len: 4096, prot: READ|WRITE, flags:
PRIVATE|ANONYMOUS, fd: -1) = 0x7f6f856ab000
<SNIP>
[acme@zoo linux]$
It works.
I guess what fixes what you report is this cset:
commit ab85785aa13c36440a91a8e9f7616357de411a1f
Author: Arnaldo Carvalho de Melo <a...@redhat.com>
Date: Mon Jul 6 08:51:41 2015 -0300
tools lib api debugfs: Check for tracefs when reporting errors
Now that we have two mountpoints, one for debugfs and another, for
tracefs, we end up needing to check permissions for both, so, on
a system with default config we were always asking the user to
check the permission of the debugfs mountpoint, even when it was
already sufficient. Fix it.
-----------
[acme@zoo linux]$ git describe ab85785aa13c36440a91a8e9f7616357de411a1f
v4.2-rc1-17-gab85785aa13c
So, can you try running the perf tools, built from the latest 4.2-rc codebase
to see if it behaves as you expect?
- Arnaldo
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