Re: [libvirt] [Qemu-devel] [PATCH v8 7/7] block: Enable qemu_open/close to work with fd sets

Am 10.08.2012 04:10, schrieb Corey Bryant: > When qemu_open is passed a filename of the "/dev/fdset/nnn" > format (where nnn is the fdset ID), an fd with matching access > mode flags will be searched for within the specified monitor > fd set. If the fd is found, a dup of the fd will be returned > from qemu_open. > > Each fd set has a reference count. The purpose of the reference > count is to determine if an fd set contains file descriptors that > have open dup() references that have not yet been closed. It is > incremented on qemu_open and decremented on qemu_close. It is > not until the refcount is zero that file desriptors in an fd set > can be closed. If an fd set has dup() references open, then we > must keep the other fds in the fd set open in case a reopen > of the file occurs that requires an fd with a different access > mode. > > Signed-off-by: Corey Bryant <coreyb(a)linux.vnet.ibm.com&gt; > @@ -78,6 +79,69 @@ int qemu_madvise(void *addr, size_t len, int advice) > #endif > } > > +/* > + * Dups an fd and sets the flags > + */ > +static int qemu_dup(int fd, int flags) qemu_dup() is probably not a good name. We'll want to use it when we need to get a wrapper around dup(). And I suspect that we will need it for making bdrv_reopen() compatible with fdset refcounting.

> +{ > + int ret; > + int serrno; > + int dup_flags; > + int setfl_flags; > + > + if (flags & O_CLOEXEC) { > +#ifdef F_DUPFD_CLOEXEC > + ret = fcntl(fd, F_DUPFD_CLOEXEC, 0); > +#else > + ret = dup(fd); > + if (ret != -1) { > + qemu_set_cloexec(ret); > + } > +#endif > + } else { > + ret = dup(fd); > + } qemu_open() is supposed to add O_CLOEXEC by itself, so I think we should execute the then branch unconditionally (or we would have to change the qemu_dup() call below to add it - but the fact that O_CLOEXEC isn't even necessarily defined doesn't help with that).