Re: [libvirt] [PATCH v3 3/5] osdep: Enable qemu_open to dup pre-opened fd

On 06/14/2012 09:55 AM, Corey Bryant wrote: I think you need to honor flags so that the end use of the fd will be as if qemu had directly opened the file, rather than just doing a blind dup with a resulting fd that is in a different state than the caller expected. I can think of at least the following cases (there may be more): if (flags & O_TRUNCATE || ((flags & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL)) ftruncate(ret, 0); Why do I truncate on O_CREAT|O_EXCL? Because that's a case where open() guarantees that the file will have just been created empty. if (flags & O_CLOEXEC) use fcntl(F_DUPFD_CLOEXEC) instead of dup(), if possible else fallback to fcntl(F_GETFD/F_SETFD) to set FD_CLOEXEC non-atomically Oh, and are we using MSG_CMSG_CLOEXEC where possible (and where not possible, falling back to fcntl(F_GETFD/F_SETFD) to set FD_CLOEXEC) on all fds received by 'getfd' and 'pass-fd'? I can't think of any reason why 'migrate fd:name' would need to be inheritable, and in the case of /dev/fd/ parsing, while the dup() result may need to be inheritable, the original that we are dup'ing from should most certainly be cloexec. if (flags & O_NONBLOCK) use fcntl(F_GETFL/F_SETFL) to set O_NONBLOCK else use fcntl(F_GETFL/F_SETFL) to clear O_NONBLOCK or maybe we document that callers of pass-fd must always pass fds with O_NONBLOCK clear instead of clearing it ourselves. Or maybe we make sure part of the process of tying name with fd in the lookup list of named fds is determining the current O_NONBLOCK state in case future qemu_open() need it in the opposite state. Treat O_APPEND similarly to O_NONBLOCK (with fcntl(F_GETFL/F_SETFL) to match the desired open() setting). -- Eric Blake eblake(a)redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org