Re: [PATCH] kernel/perf: correct return code of rb_alloc_aux() if !has_aux(ev)

From: Alexander Shishkin
Date: Tue Jun 20 2017 - 08:26:11 EST

Hendrik Brueckner <brueckner@xxxxxxxxxxxxxxxxxx> writes:

> If the event for which an AUX area is about to be allocated, does
> not support setting up an AUX area, rb_alloc_aux() return -ENOTSUPP.
> This error condition is being returned unfiltered to the user space,
> and, for example, the perf tools fails with:
> failed to mmap with 524 (INTERNAL ERROR: strerror_r(524, 0x3fff497a1c8, 512)=22)
> This error can be easily seen with "perf record -m 128,256 -e cpu-clock".
> The 524 error code maps to -ENOTSUPP (in rb_alloc_aux()). The -ENOTSUPP
> error code shall be only used within the kernel. So the correct error
> code would then be -EOPNOTSUPP.
> With this commit, the perf tool then reports:
> failed to mmap with 95 (Operation not supported)
> which is more clear.

Acked-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>

Curious as to why does the tool allow this.