Re: [Libguestfs] [PATCH nbdkit v3 5/6] server: debug: Fix error handling

On Tue, May 09, 2023 at 03:51:20PM +0100, Richard W.M. Jones wrote: > Preserve errno even if the function fails. We need to set > errno = err again on every exit path out of the function. > > Check if close_memstream failed and go to the error path if so. This > is most important on Windows where close_memstream is what actually > allocates the memory. But even on Unix, close_memstream (which is an > alias for fclose) can return an error. > > Move the error-handling code to the end of the function. > > I added a comment above the 'fputs' explaining why exactly we're using > memstream in the first place -- because it is more atomic than using > multiple fprintf. > > See: https://listman.redhat.com/archives/libguestfs/2023-May/031456.html > Thanks: Laszlo Ersek > --- > server/debug.c | 28 ++++++++++++++++------------ > 1 file changed, 16 insertions(+), 12 deletions(-) Reviewed-by: Eric Blake <eblake(a)redhat.com&gt; > + fail: > + /* Try to emit what we can. */ > + errno = err; > + vfprintf (stderr, fs, args); > + fprintf (stderr, "\n"); > errno = err; It might make more sense if the first line were written: errno = err; /* In case fs uses %m */ so that no one tries to "optimize" out what looks like a redundant assignment when both are really required.