From 0c470f5563c3d5d769dcffaae432e2df78fcc79e Mon Sep 17 00:00:00 2001 From: FRIGN Date: Sun, 5 Apr 2015 00:04:58 +0200 Subject: [PATCH] Remove fflush-check from fshut() Basically, it's a conflict between POSIX and ISO C what do to when input streams are passed to fflush(). POSIX mandates that the seeking-position should be synced, but ISO C says it's undefined behaviour. We love POSIX, but the standard-documents specify that in all conflict cases, ISO C wins, so this breaks with EBADF on BSD's. musl and glibc follow POSIX behaviour, which makes sense, but involves numerous portability concerns. To get around this, we just don't check fflush() and rely on the fact that no implementation sets ferror on the file-stream in fflush if it is an input stream, so every issue caught in fflush() is caught later with ferror() and fclose(). Add a comment to fshut() because this stuff is so complicated, it took us a day to figure out. --- libutil/fshut.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/libutil/fshut.c b/libutil/fshut.c index f243a82..4de6596 100644 --- a/libutil/fshut.c +++ b/libutil/fshut.c @@ -7,10 +7,12 @@ int fshut(FILE *fp, const char *fname) { int ret = 0; - if (fflush(fp) && !ret) { - weprintf("fflush %s:", fname); - ret = 1; - } + /* fflush() is undefined for input streams by ISO C, + * but not POSIX 2008 if you ignore ISO C overrides. + * Leave it unchecked an rely on the following + * functions to detect errors. + */ + fflush(fp); if (ferror(fp) && !ret) { weprintf("ferror %s:", fname);