Note about acpi_get_table_header

Note about acpi_get_table_header

[Jean Delvare]

Hello,

The description block before acpi_get_table_header() in
drivers/acpi/acpica/tbxface.c includes the following comment:

 * NOTE:        Caller is responsible in unmapping the header with
 *              acpi_os_unmap_memory

However, looking at the code, it seems that we are already calling
acpi_os_unmap_memory() internally as appropriate, and we always return
a copy of the header, not a pointer to it. So I see no reason why the
caller would ever need to call acpi_os_unmap_memory(). As a matter of
fact the only current caller of this function does NOT call
acpi_os_unmap_memory() afterwards.

So I believe this note is wrong and should be removed?

Thanks,
-- 
Jean Delvare
SUSE L3 Support

Re: Note about acpi_get_table_header

[Hanjun Guo]

On 2020/2/4 17:17, Jean Delvare wrote:
> Hello,
> 
> The description block before acpi_get_table_header() in
> drivers/acpi/acpica/tbxface.c includes the following comment:
> 
>  * NOTE:        Caller is responsible in unmapping the header with
>  *              acpi_os_unmap_memory

I'm confused as well when I was reading the code.

> 
> However, looking at the code, it seems that we are already calling
> acpi_os_unmap_memory() internally as appropriate, and we always return
> a copy of the header, not a pointer to it. So I see no reason why the
> caller would ever need to call acpi_os_unmap_memory(). As a matter of
> fact the only current caller of this function does NOT call
> acpi_os_unmap_memory() afterwards.
> 
> So I believe this note is wrong and should be removed?

I think so.

Thanks
Hanjun

RE: Note about acpi_get_table_header

[Moore, Robert]

-----Original Message-----
From: Hanjun Guo <guohanjun@huawei.com> 
Sent: Tuesday, February 04, 2020 2:05 AM
To: Jean Delvare <jdelvare@suse.de>; linux-acpi@vger.kernel.org
Cc: Moore, Robert <robert.moore@intel.com>; Kaneda, Erik <erik.kaneda@intel.com>; Wysocki, Rafael J <rafael.j.wysocki@intel.com>
Subject: Re: Note about acpi_get_table_header

On 2020/2/4 17:17, Jean Delvare wrote:
> Hello,
> 
> The description block before acpi_get_table_header() in 
> drivers/acpi/acpica/tbxface.c includes the following comment:
> 
>  * NOTE:        Caller is responsible in unmapping the header with
>  *              acpi_os_unmap_memory

I'm confused as well when I was reading the code.

> 
> However, looking at the code, it seems that we are already calling
> acpi_os_unmap_memory() internally as appropriate, and we always return 
> a copy of the header, not a pointer to it. So I see no reason why the 
> caller would ever need to call acpi_os_unmap_memory(). As a matter of 
> fact the only current caller of this function does NOT call
> acpi_os_unmap_memory() afterwards.
> 
> So I believe this note is wrong and should be removed?

Yes, the note is obsolete. I'll remove it.

Bob

I think so.

Thanks
Hanjun