Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/1] block: improve error handling in raw_open

[Max Reitz]

On 26.07.2016 20:03, Sascha Silbe wrote:
> Dear Max,
> 
> Max Reitz <address@hidden> writes:
> 
>> We don't guarantee that error_setg_errno() does not modify errno. (In
>> practice it should not, but we don't guarantee that.)
> 
> I agree it's a good general policy to _not_ rely on the callee
> explicitly saving and restoring errno. Especially since C11 pretty much
> allows any "library function" (including e.g. va_start()) to clobber
> errno...
> 
> In the case of error_setg_errno() it would be helpful to mention that in
> the API docs. The current implementation goes out of its way to preserve
> errno, so callers might come to rely on it.
> 
> So how about:
> 
>  /*
>   * 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.
> + *
> + * Reminder: errno may get clobbered by almost any function call. If
> + * you need the value of errno for another purpose, save it before
> + * invoking error_setg_errno() (or any other function for that
> + * matter).
>   */
>  #define error_setg_errno(errp, os_error, fmt, ...)                      \
>      error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \
>                                (os_error), (fmt), ## __VA_ARGS__)
> 
> (I can prepare a proper patch if you agree with the above.)

Thanks, that sounds good to me.

Max

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