On 6/3/21 11:22 PM, Steven Rostedt wrote:
> On Fri, 14 May 2021 22:51:14 +0200
> Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
>
>> Provides a generic read and write implementation to save/read u64 values
>> from a file on tracefs. The trace_ull_config structure defines where to
>> read/write the value, the min and the max acceptable values, and a lock
>> to protect the write.
>
> This states what the patch is doing, but does not say why it is doing it.
Yeah...
>>
>> Cc: Jonathan Corbet <corbet@xxxxxxx>
>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
>> Cc: Clark Willaims <williams@xxxxxxxxxx>
>> Cc: John Kacur <jkacur@xxxxxxxxxx>
>> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
>> Cc: linux-doc@xxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
>> ---
>> kernel/trace/trace.c | 87 ++++++++++++++++++++++++++++++++++++++++++++
>> kernel/trace/trace.h | 19 ++++++++++
>> 2 files changed, 106 insertions(+)
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 560e4c8d3825..b4cd89010813 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -7516,6 +7516,93 @@ static const struct file_operations snapshot_raw_fops = {
>>
>> #endif /* CONFIG_TRACER_SNAPSHOT */
>>
>> +/*
>> + * trace_ull_config_write - Generic write function to save u64 value
>
>
> That is a horrible name. What the hell is the "config"?
>
>> + * @filp: The active open file structure
>> + * @ubuf: The userspace provided buffer to read value into
>> + * @cnt: The maximum number of bytes to read
>> + * @ppos: The current "file" position
>> + *
>> + * This function provides a generic write implementation to save u64 values
>> + * from a file on tracefs. The filp->private_data must point to a
>> + * trace_ull_config structure that defines where to write the value, the
>> + * min and the max acceptable values, and a lock to protect the write.
>
> This doesn't seem to be a generic way to save 64 bit values (which I still
> don't understand, because unsigned long long should work too). But it looks
> like the rational is for having some kind of generic way to read 64 bit
> values giving them a min and a max.
>
> I see this is used later, but this patch needs to be rewritten. It makes no
> sense.
The reason for this patch is that hwlat, osnoise, and timerlat have "u64 config"
options that are read/write via tracefs "files." In the previous version, I had
multiple functions doing basically the same thing:
A write function that:
read a u64 from user-space
get a lock,
check for min/max acceptable values
save the value
release the lock.
and a read function that:
write the config value to the "read" buffer.
And so, I tried to come up with a way to avoid code duplication.
question: are only the names that are bad? (I agree that they are bad) or do you
think that the overall idea is bad? :-)
Suggestions?
-- Daniel
> -- Steve
