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

On 08/10/2012 12:34 PM, Kevin Wolf wrote: > 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. > Do you you have a suggestion for a name? >> +{ >> + 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). Sure I can modify this to always add O_CLOEXEC. (I know you mentioned this before but I think I interpreted the comment as a question to others.) Do you also want me to modify qemu_open to always add O_CLOEXEC?