diff options
| -rw-r--r-- | net/tap-linux.c | 13 | ||||
| -rw-r--r-- | qemu-options.hx | 2 |
2 files changed, 10 insertions, 5 deletions
diff --git a/net/tap-linux.c b/net/tap-linux.c index f7aa9041b8..ff8cad0ea0 100644 --- a/net/tap-linux.c +++ b/net/tap-linux.c @@ -82,12 +82,17 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required return fd; } -/* sndbuf should be set to a value lower than the tx queue - * capacity of any destination network interface. +/* sndbuf implements a kind of flow control for tap. + * Unfortunately when it's enabled, and packets are sent + * to other guests on the same host, the receiver + * can lock up the transmitter indefinitely. + * + * To avoid packet loss, sndbuf should be set to a value lower than the tx + * queue capacity of any destination network interface. * Ethernet NICs generally have txqueuelen=1000, so 1Mb is - * a good default, given a 1500 byte MTU. + * a good value, given a 1500 byte MTU. */ -#define TAP_DEFAULT_SNDBUF 1024*1024 +#define TAP_DEFAULT_SNDBUF 0 int tap_set_sndbuf(int fd, QemuOpts *opts) { diff --git a/qemu-options.hx b/qemu-options.hx index 939297a1b0..598a1bdf77 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -1057,7 +1057,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net, " use '[down]script=no' to disable script execution\n" " use 'fd=h' to connect to an already opened TAP interface\n" " use 'sndbuf=nbytes' to limit the size of the send buffer (the\n" - " default of 'sndbuf=1048576' can be disabled using 'sndbuf=0')\n" + " default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')\n" " use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap flag\n" " use vnet_hdr=on to make the lack of IFF_VNET_HDR support an error condition\n" " use vhost=on to enable experimental in kernel accelerator\n" |