On 11/14/2016 11:20 PM, dwilder wrote: > The example code in netlink(7) (for reading netlink message) suggests > using > a 4k read buffer with recvmsg. This can cause truncated messages on > systems > using a page size is >4096. Please see: > linux/include/linux/netlink.h (in the kernel source) > > <snip> > /* > * skb should fit one page. This choice is good for headerless > malloc. > * But we should limit to 8K so that userspace does not have to > * use enormous buffer sizes on recvmsg() calls just to avoid > * MSG_TRUNC when PAGE_SIZE is very large. > */ > #if PAGE_SIZE < 8192UL > #define NLMSG_GOODSIZE SKB_WITH_OVERHEAD(PAGE_SIZE) > #else > #define NLMSG_GOODSIZE SKB_WITH_OVERHEAD(8192UL) > #endif > > #define NLMSG_DEFAULT_SIZE (NLMSG_GOODSIZE - NLMSG_HDRLEN) > <snip> > > I was troubleshooting some up-stream code on a ppc64le system > (page:size of 64k) This code had duplicated the example from netlink(7) > and > was using a 4k buffer. On x86-64 with a 4k page size this is not a > problem, > however on the 64k page system some messages were truncated. Using an > 8k buffer > as implied in netlink.h prevents problems with any page size. > > Lets change the example so others don't propagate the problem further. > > Signed-off-by David Wilder <dwilder@xxxxxxxxxx> Thanks, David. Patch applied. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
