| Message ID | 1462237265-61763-3-git-send-email-chrisfriedt@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Christopher Friedt <chrisfriedt@gmail.com> writes: > The file ivshmem.c unconditionally references event_notifier_init_fd() in util/event_notifier-posix.c, even if CONFIG_EVENTFD is not defined. On platforms where CONFIG_POSIX is defined, but CONFIG_EVENTFD is not defined, that results in an undefined symbol referenced from ivshmem.c and the link fails. That applies to Mac OS X, but possibly other BSD-based distros. ivshmem.c cannot work without CONFIG_EVENTFD, and therefore is not compiled without it. A link error for event_notifier_init_fd() from ivshmem.o indicates you got CONFIG_EVENTFD=y for make (since ivshmem.o gets linked), but !defined(CONFIG_EVENTFD) for C (or else event_notifier_init_fd() would exist). Your build tree is messed up, or the makefiles are broken. Try starting over with a fresh build tree. See also http://lists.nongnu.org/archive/html/qemu-devel/2016-04/msg01437.html > Note: there is nothing specific to eventfd inside and event_notifier_init() also fails unconditionally if CONFIG_EVENTFD is not defined. I'm afraid you're misreading the code. event_notifier_init() has a working fallback: if the host doesn't support eventfd (!defined(CONFIG_EVENTFD) or eventfd() fails with ENOSYS), then we emulate eventfd with a pair of pipes. Possible only because pipes have special properties. To support the emulation, we have two file descriptors, @rfd for reading and @wfd for writing. Design invariant: if they are the same file descriptor, it must be a proper eventfd, and if they are different, they must be a pair of pipes. The only way to establish the invariant with event_notifier_init_fd() is passing it an eventfd, as the function's contract says. Without CONFIG_EVENTFD, there is no way to use the function correctly, so defining it would be nothing but a trap. See also commit 330b583, which added the ifdef. > Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com> > --- > util/event_notifier-posix.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/util/event_notifier-posix.c b/util/event_notifier-posix.c > index c1f0d79..c9bb34d 100644 > --- a/util/event_notifier-posix.c > +++ b/util/event_notifier-posix.c > @@ -21,7 +21,6 @@ > #include <sys/eventfd.h> > #endif > > -#ifdef CONFIG_EVENTFD > /* > * Initialize @e with existing file descriptor @fd. > * @fd must be a genuine eventfd object, emulation with pipe won't do. > @@ -31,7 +30,6 @@ void event_notifier_init_fd(EventNotifier *e, int fd) > e->rfd = fd; > e->wfd = fd; > } > -#endif > > int event_notifier_init(EventNotifier *e, int active) > { NAK
diff --git a/util/event_notifier-posix.c b/util/event_notifier-posix.c index c1f0d79..c9bb34d 100644 --- a/util/event_notifier-posix.c +++ b/util/event_notifier-posix.c @@ -21,7 +21,6 @@ #include <sys/eventfd.h> #endif -#ifdef CONFIG_EVENTFD /* * Initialize @e with existing file descriptor @fd. * @fd must be a genuine eventfd object, emulation with pipe won't do. @@ -31,7 +30,6 @@ void event_notifier_init_fd(EventNotifier *e, int fd) e->rfd = fd; e->wfd = fd; } -#endif int event_notifier_init(EventNotifier *e, int active) {
The file ivshmem.c unconditionally references event_notifier_init_fd() in util/event_notifier-posix.c, even if CONFIG_EVENTFD is not defined. On platforms where CONFIG_POSIX is defined, but CONFIG_EVENTFD is not defined, that results in an undefined symbol referenced from ivshmem.c and the link fails. That applies to Mac OS X, but possibly other BSD-based distros. Note: there is nothing specific to eventfd inside and event_notifier_init() also fails unconditionally if CONFIG_EVENTFD is not defined. Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com> --- util/event_notifier-posix.c | 2 -- 1 file changed, 2 deletions(-)