Re: [Qemu-devel] Re: [PATCH 1/2] qemu-io: retry fgets() when errno is EINTRg

[Jamie Lokier <jamie@shareable.org>]

Kevin Wolf wrote:
> Am 16.06.2010 18:52, schrieb MORITA Kazutaka:
> > At Wed, 16 Jun 2010 13:04:47 +0200,
> > Kevin Wolf wrote:
> >>
> >> Am 15.06.2010 19:53, schrieb MORITA Kazutaka:
> >>> posix-aio-compat sends a signal in aio operations, so we should
> >>> consider that fgets() could be interrupted here.
> >>>
> >>> Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
> >>> ---
> >>>  cmd.c |    3 +++
> >>>  1 files changed, 3 insertions(+), 0 deletions(-)
> >>>
> >>> diff --git a/cmd.c b/cmd.c
> >>> index 2336334..460df92 100644
> >>> --- a/cmd.c
> >>> +++ b/cmd.c
> >>> @@ -272,7 +272,10 @@ fetchline(void)
> >>>  		return NULL;
> >>>  	printf("%s", get_prompt());
> >>>  	fflush(stdout);
> >>> +again:
> >>>  	if (!fgets(line, MAXREADLINESZ, stdin)) {
> >>> +		if (errno == EINTR)
> >>> +			goto again;
> >>>  		free(line);
> >>>  		return NULL;
> >>>  	}
> >>
> >> This looks like a loop replaced by goto (and braces are missing). What
> >> about this instead?
> >>
> >> do {
> >>     ret = fgets(...)
> >> } while (ret == NULL && errno == EINTR)
> >>
> >> if (ret == NULL) {
> >>    fail
> >> }
> >>
> > 
> > I agree.
> > 
> > However, it seems that my second patch have already solved the
> > problem.  We register this readline routines as an aio handler now, so
> > fgets() does not block and cannot return with EINTR.
> > 
> > This patch looks no longer needed, sorry.
> 
> Good point. Thanks for having a look.

Anyway, are you sure stdio functions can be interrupted with EINTR?
Linus reminds us that some stdio functions have to retry internally
anyway:

http://comments.gmane.org/gmane.comp.version-control.git/18285

-- Jamie