cc libvirt-users for more inputs Hi, I'm trying to find out how to check sndbuf for a tap device, could you please help to check it? In kernel 2.6.18, the tap device's default sndbuf is 1MB. There is a RFE bug[1] and patch[2] to introduce the option below in libvirt to adjust the sndbuf. <tune> <sndbuf>1600</sndbuf> </tune> It is said in the patch[2] that when we set sndbuf=0, we actually set it to 0xffffffff. How to check if it is set successfully? I have checked the below files, the value didn't change after I start a vm with sndbuf=0 # grep . /proc/sys/net/core/*mem_default /proc/sys/net/core/rmem_default:212992 /proc/sys/net/core/wmem_default:212992 And from the doc[3]: "The default value is set by the /proc/sys/net/core/wmem_default file and the maximum allowed value is set by the /proc/sys/net/core/wmem_max file." Current kernel 5.14.0-177.el9 has some updates about sndbuf: # cat /proc/sys/net/core/wmem_default 212992 # cat /proc/sys/net/core/wmem_max 212992 Thank you! [1] Bug 665293 <https://bugzilla.redhat.com/show_bug.cgi?id=665293> - RFE: Allow setting size of send buffer per TAP device in QEMU driver [2] https://listman.redhat.com/archives/libvir-list/2011-January/032763.html [3] https://man7.org/linux/man-pages/man7/socket.7.html Yalan