Re: [libvirt] [PATCH] virsh: properly interleave shared stdout and stderr

Without this patch, invoking 'virsh>file 2>&1' results in error messages appearing before normal output, even if they occurred later in time than the normal output (since stderr is unbuffered, but stdout waits until a full buffer). * tools/virsh.c (print_job_progress, vshError): Flush between stream transitions. * tests/undefine: Test it. --- This fixes the bug I mentioned here: https://www.redhat.com/archives/libvir-list/2011-August/msg00891.html tests/undefine | 5 +---- tools/virsh.c | 8 ++++++++ 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/tests/undefine b/tests/undefine index 6c821ad..22d6c14 100755 --- a/tests/undefine +++ b/tests/undefine @@ -58,17 +58,14 @@ compare exp out || fail=1 # Succeed, now: first shut down, then undefine, both via name. $abs_top_builddir/tools/virsh -q -c test:///default \ - 'shutdown test; undefine test; dominfo test'> out 2> err + 'shutdown test; undefine test; dominfo test'> out 2>&1 test $? = 1 || fail=1 cat<<\EOF> expout || fail=1 Domain test is being shutdown Domain test has been undefined -EOF -cat<<\EOF> experr || fail=1 error: failed to get domain 'test' error: Domain not found EOF compare expout out || fail=1 -compare experr err || fail=1 (exit $fail); exit $fail diff --git a/tools/virsh.c b/tools/virsh.c index 1c67150..7d849ec 100644 --- a/tools/virsh.c +++ b/tools/virsh.c @@ -4956,7 +4956,10 @@ print_job_progress(const char *label, unsigned long long remaining, } } + /* see comments in vshError about why we must flush */ + fflush(stdout); fprintf(stderr, "\r%s: [%3d %%]", label, progress); + fflush(stderr); } static bool @@ -14336,6 +14339,10 @@ vshError(vshControl *ctl, const char *format, ...) va_end(ap); } + /* Most output is to stdout, but if someone ran virsh 2>&1, then + * printing to stderr will not interleave correctly with stdout + * unless we flush between every transition between streams. */ + fflush(stdout); fputs(_("error: "), stderr); va_start(ap, format); @@ -14345,6 +14352,7 @@ vshError(vshControl *ctl, const char *format, ...) va_end(ap); fprintf(stderr, "%s\n", NULLSTR(str)); + fflush(stderr); VIR_FREE(str); }