Re: [Qemu-devel] [PATCH] error: error_setg_errno(): errno gets preserved

[Markus Armbruster]

Sascha Silbe <address@hidden> writes:

> Dear Eric,
>
> Eric Blake <address@hidden> writes:
>
>>> +++ b/include/qapi/error.h
>>> @@ -170,6 +170,9 @@ void error_setg_internal(Error **errp,
>>>   * Just like error_setg(), with @os_error info added to the message.
>>>   * If @os_error is non-zero, ": " + strerror(os_error) is appended to
>>>   * the human-readable error message.
>>> + *
>>> + * The value of errno (which usually can get clobbered by almost any
>>> + * function call) will be preserved.
>>>   */
>>>  #define error_setg_errno(errp, os_error, fmt, ...)                      \
>>>      error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \
>>
>> Do we need/want to make the guarantee of preserving errno across any of
>> the other functions and macros declared in error.h?
>
> It would be more consistent to have all error reporting functions
> promise this, even if they do not get passed the errno. In some cases
> the errno might not matter to the user (so error_setg_errno() isn't
> used), but still be passed on to the caller to signal an error (so
> clobbering it could be problematic).
>
> Can prepare a follow-up patch that makes sure error_setg(),
> error_propagate(), error_setg_file_open(), error_set() preserve
> errno. Optionally also the other functions listed in
> include/qapi/error.h and include/qemu/error-report.h.

Suggest:

* A patch to document existing errno-preserving behavior.

* Patches to reduce inconsistency, if any.  E.g. say all but one
  error_setg() function preserve errno, make the exception preserve it,
  too.

* Optionally, patches to add more errno-preserving behavior you consider
  useful.  I can't promise such patches will be applied, only that they
  will be reviewed :)