Re: [Qemu-devel] [PATCH v6 2/8] device_tree: introduce load_device_tree_from_sysfs

[Eric Auger <eric.auger@linaro.org>]

On 02/01/2016 05:27 PM, Rob Herring wrote:
> On Mon, Feb 1, 2016 at 10:22 AM, Eric Auger <eric.auger@linaro.org> wrote:
>> Hi Rob,
>> On 02/01/2016 05:15 PM, Rob Herring wrote:
>>> On Mon, Feb 1, 2016 at 7:51 AM, Eric Auger <eric.auger@linaro.org> wrote:
>>>> This function returns the host device tree blob from sysfs
>>>> (/proc/device-tree). It uses a recursive function inspired
>>>> from dtc read_fstree.
>>>>
>>>> Signed-off-by: Eric Auger <eric.auger@linaro.org>
>>>>
>>>> ---
>>>> v5 -> v6:
>>>> - fix some spelling mistakes
>>>> - error_report + exit replaced by error_setg
>>>> - const char *parent_node;
>>>> - use g_strdup_printf instead of g_strjoin
>>>> - add a doc comment for load_device_tree_from_sysfs
>>>> v1 -> v2:
>>>> - do not implement/expose read_fstree and load_device_tree_from_sysfs
>>>>   if CONFIG_LINUX is not defined (lstat is not implemeted in mingw)
>>>> - correct indentation in read_fstree
>>>> - use /proc/device-tree symlink instead of /sys/firmware/devicetree/base
>>>>   path (kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-ofw)
>>>> - use g_file_get_contents in read_fstree
>>>> - introduce SYSFS_DT_BASEDIR macro and use strlen
>>>> - exit on error in load_device_tree_from_sysfs
>>>> - user error_setg
>>>>
>>>> RFC -> v1:
>>>> - remove runtime dependency on dtc binary and introduce read_fstree
>>>> ---
>>>>  device_tree.c                | 99 ++++++++++++++++++++++++++++++++++++++++++++
>>>>  include/sysemu/device_tree.h |  8 ++++
>>>>  2 files changed, 107 insertions(+)
>>>>
>>>> diff --git a/device_tree.c b/device_tree.c
>>>> index a9f5f8e..3797182 100644
>>>> --- a/device_tree.c
>>>> +++ b/device_tree.c
>>>> @@ -17,6 +17,9 @@
>>>>  #include <fcntl.h>
>>>>  #include <unistd.h>
>>>>  #include <stdlib.h>
>>>> +#ifdef CONFIG_LINUX
>>>> +#include <dirent.h>
>>>> +#endif
>>>>
>>>>  #include "qemu-common.h"
>>>>  #include "qemu/error-report.h"
>>>> @@ -117,6 +120,102 @@ fail:
>>>>      return NULL;
>>>>  }
>>>>
>>>> +#ifdef CONFIG_LINUX
>>>> +
>>>> +#define SYSFS_DT_BASEDIR "/proc/device-tree"
>>>
>>> Use the sysfs path (/sys/firmware/device-tree/ IIRC) as this is just a
>>> symlink to sysfs and /proc is considered the legacy path.
>> I used the sysfs originally but I eventually found:
>> https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-ofw
>> which states:
>>
>> "Userspace must not use the /sys/firmware/devicetree/base
>> path directly, but instead should follow /proc/device-tree
>> symlink. It is possible that the absolute path will change
>> in the future, but the symlink is the stable ABI.
>> "
>>
>> Do you confirm this statement is outdated.
> 
> Ah, no. My memory is just wrong. NM.

OK no problem.

Thanks for taking care

Best Regards

Eric
> 
> Rob
>