Re: [PATCH v2] xfs_scrub: fix strerror_r usage yet again

[Christoph Hellwig <hch@infradead.org>]

On Tue, Sep 23, 2025 at 05:53:53PM -0700, Darrick J. Wong wrote:
> On Mon, Sep 22, 2025 at 10:01:17AM -0700, Christoph Hellwig wrote:
> > The autoconf maigc looks good (as good as autoconf can look anyway),
> > but why is this code using strerror_r to start with?  AFAIK on Linux
> > strerror is using thread local storage since the damn of time, so
> > just doing this as:
> > 
> > 	fprintf(stream, _("%s."), strerror(error));
> > 
> > should be perfectly fine, while also simpler and more portable.
> 
> But there's no guarantee that the implementation does this, is there?
> The manpage doesn't say anything like that.

To me this pretty clear reads that the return string is stable until
the next call to strerror as long as you only use it in the calling
thread:

"The strerror() function returns a pointer to a string that describes
the error code passed in the argument errnum,  ...
This string must not be modified by the application, and the returned
pointer will be invalidated on a subsequent call to strerror() or
strerror_l(), or if the thread that obtained the string exits.  No
other library function, including perror(3), will modify this string."