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

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

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Do you confirm this statement is outdated.

Thank you in advance

Best Regards

Eric
> 
> Rob
>