On Wed, Sep 07, 2011 at 05:22:00PM +0200, Patrick McHardy wrote: > On 04.09.2011 18:18, Michał Mirosław wrote: > > On Sat, Sep 03, 2011 at 07:26:08PM +0200, kaber@xxxxxxxxx wrote: > >> From: Patrick McHardy <kaber@xxxxxxxxx> > >> > >> Add support for memory mapped sendmsg() to netlink. Userspace queued to > >> be processed frames into the TX ring and invokes sendmsg with > >> msg.iov.iov_base = NULL to trigger processing of all pending messages. > >> > >> Since the kernel usually performs full message validation before beginning > >> processing, userspace must be prevented from modifying the message > >> contents while the kernel is processing them. In order to do so, the > >> frames contents are copied to an allocated skb in case the the ring is > >> mapped more than once or the file descriptor is shared (f.i. through > >> AF_UNIX file descriptor passing). > >> > >> Otherwise an skb without a data area is allocated, the data pointer set > >> to point to the data area of the ring frame and the skb is processed. > >> Once the skb is freed, the destructor releases the frame back to userspace > >> by setting the status to NL_MMAP_STATUS_UNUSED. > > > > Is this protected from threads? Like: one thread waits on sendmsg() and > > another (same process) changes the buffer. > Yes, if the ring is mapped multiple times (or the file descriptor > is changed), the contents are copied to an allocated skb. I mean: [1] mmap() [1] fill buffers [1] pthread_create() [creates: 2] [1] sendmsg() starts [2] modify buffers [1] sendmsg() returns So: no multiple mmaps, and no touching of the fd. I haven't dug into filesystem layer to see if threads affect file->f_count, but there sure are no multiple mappings here. Best Regards, Michał Mirosław -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
