[U-Boot] [PATCH 2/2] tools: env: Implement atomic replace for filesystem

[Alex Kiernan]

On Fri, Mar 9, 2018 at 10:03 AM, Stefano Babic <sbabic at denx.de> wrote:
> On 09/03/2018 10:54, Alex Kiernan wrote:
>> On Thu, Mar 8, 2018 at 5:04 PM, Stefano Babic <sbabic at denx.de> wrote:
>>> Hi alex,
>>>
>>> On 08/03/2018 12:52, Alex Kiernan wrote:
>>>> If the U-Boot environment is stored in a regular file and redundant
>>>> operation isn't set, then write to a temporary file and perform an
>>>> atomic rename.
>>>>
>>>
>>> Even if it is not explicitely set (IMHO it should), this code can
>>> be used as library and linked to own application. That means that
>>> concurrency can happens. I mean:
>>>
>>
>> At this point you're writing the new environment, so we should hold a
>> lock to avoid concurrent writes.
>
> This is already done, even if not in the way I like.
> tools/env/fw_env_main.c calls flock() to acquire the resource. This
> works using fw_printenv / fw_setenv, but not as library. Library's users
> as me have to provide themselves a lock before calling the fw_* functions.
>

True... that particular implementation also causes me a different
problem in that it fails on a read-only fs and I have a need for a
call to fw_printenv before the filesystem has gone read-write.

-- 
Alex Kiernan