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Re: [Qemu-devel] [PATCH] slirp: Read host DNS config on demand
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] slirp: Read host DNS config on demand |
Date: |
Sun, 2 Aug 2009 10:43:52 +0300 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Fri, Jul 31, 2009 at 06:10:22PM -0700, Ed Swierk wrote:
> Currently the qemu user-mode networking stack reads the host DNS
> configuration (/etc/resolv.conf or the Windows equivalent) only once
> when qemu starts. This causes name lookups in the guest to fail if the
> host is moved to a different network from which the original DNS servers
> are unreachable, a common occurrence when the host is a laptop.
>
> This patch changes the slirp code to read the host DNS configuration on
> demand, caching the results for 10 seconds to avoid unnecessary overhead
> if name lookups occur in rapid succession.
>
> Signed-off-by: Ed Swierk <address@hidden>
> Acked-by: Jan Kiszka <address@hidden>
Introducing a random delay until update might surprise users.
Would it make sense to use something like inotify instead?
> ---
> diff --git a/slirp/ip_icmp.c b/slirp/ip_icmp.c
> index 95a4b39..751a8e2 100644
> --- a/slirp/ip_icmp.c
> +++ b/slirp/ip_icmp.c
> @@ -127,7 +127,8 @@ icmp_input(struct mbuf *m, int hlen)
> slirp->vnetwork_addr.s_addr) {
> /* It's an alias */
> if (so->so_faddr.s_addr == slirp->vnameserver_addr.s_addr) {
> - addr.sin_addr = dns_addr;
> + if (get_dns_addr(&addr.sin_addr) < 0)
> + addr.sin_addr = loopback_addr;
> } else {
> addr.sin_addr = loopback_addr;
> }
> diff --git a/slirp/libslirp.h b/slirp/libslirp.h
> index 93087ed..67c70e3 100644
> --- a/slirp/libslirp.h
> +++ b/slirp/libslirp.h
> @@ -8,6 +8,8 @@
> struct Slirp;
> typedef struct Slirp Slirp;
>
> +int get_dns_addr(struct in_addr *pdns_addr);
> +
> Slirp *slirp_init(int restricted, struct in_addr vnetwork,
> struct in_addr vnetmask, struct in_addr vhost,
> const char *vhostname, const char *tftp_path,
> diff --git a/slirp/main.h b/slirp/main.h
> index 28d92d8..e87b068 100644
> --- a/slirp/main.h
> +++ b/slirp/main.h
> @@ -32,7 +32,6 @@ extern u_int curtime;
> extern fd_set *global_readfds, *global_writefds, *global_xfds;
> extern struct in_addr our_addr;
> extern struct in_addr loopback_addr;
> -extern struct in_addr dns_addr;
> extern char *username;
> extern char *socket_path;
> extern int towrite_max;
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index e883f82..987aad9 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -29,8 +29,6 @@
>
> /* host address */
> struct in_addr our_addr;
> -/* host dns address */
> -struct in_addr dns_addr;
> /* host loopback address */
> struct in_addr loopback_addr;
>
> @@ -51,9 +49,12 @@ static int do_slowtimo;
> TAILQ_HEAD(slirp_instances, Slirp) slirp_instances =
> TAILQ_HEAD_INITIALIZER(slirp_instances);
>
> +struct in_addr dns_addr = { 0 };
> +u_int dns_addr_time = 0;
> +
> #ifdef _WIN32
>
> -static int get_dns_addr(struct in_addr *pdns_addr)
> +int get_dns_addr(struct in_addr *pdns_addr)
> {
> FIXED_INFO *FixedInfo=NULL;
> ULONG BufLen;
> @@ -61,6 +62,11 @@ static int get_dns_addr(struct in_addr *pdns_addr)
> IP_ADDR_STRING *pIPAddr;
> struct in_addr tmp_addr;
>
> + if (dns_addr.s_addr != 0 && (curtime - dns_addr_time) < 10000) {
> + *pdns_addr = dns_addr;
> + return 0;
> + }
> +
> FixedInfo = (FIXED_INFO *)GlobalAlloc(GPTR, sizeof(FIXED_INFO));
> BufLen = sizeof(FIXED_INFO);
>
> @@ -84,6 +90,8 @@ static int get_dns_addr(struct in_addr *pdns_addr)
> pIPAddr = &(FixedInfo->DnsServerList);
> inet_aton(pIPAddr->IpAddress.String, &tmp_addr);
> *pdns_addr = tmp_addr;
> + dns_addr = tmp_addr;
> + dns_addr_time = curtime;
> if (FixedInfo) {
> GlobalFree(FixedInfo);
> FixedInfo = NULL;
> @@ -98,7 +106,7 @@ static void winsock_cleanup(void)
>
> #else
>
> -static int get_dns_addr(struct in_addr *pdns_addr)
> +int get_dns_addr(struct in_addr *pdns_addr)
> {
> char buff[512];
> char buff2[257];
> @@ -106,6 +114,11 @@ static int get_dns_addr(struct in_addr *pdns_addr)
> int found = 0;
> struct in_addr tmp_addr;
>
> + if (dns_addr.s_addr != 0 && (curtime - dns_addr_time) < 10000) {
> + *pdns_addr = dns_addr;
> + return 0;
> + }
> +
> f = fopen("/etc/resolv.conf", "r");
> if (!f)
> return -1;
> @@ -120,8 +133,11 @@ static int get_dns_addr(struct in_addr *pdns_addr)
> if (tmp_addr.s_addr == loopback_addr.s_addr)
> tmp_addr = our_addr;
> /* If it's the first one, set it to dns_addr */
> - if (!found)
> + if (!found) {
> *pdns_addr = tmp_addr;
> + dns_addr = tmp_addr;
> + dns_addr_time = curtime;
> + }
> #ifdef DEBUG
> else
> lprint(", ");
> @@ -177,11 +193,6 @@ static void slirp_init_once(void)
> if (our_addr.s_addr == 0) {
> our_addr = loopback_addr;
> }
> -
> - /* FIXME: This address may change during runtime */
> - if (get_dns_addr(&dns_addr) < 0) {
> - dns_addr = loopback_addr;
> - }
> }
>
> static void slirp_state_save(QEMUFile *f, void *opaque);
> diff --git a/slirp/socket.c b/slirp/socket.c
> index d8fbe89..207109c 100644
> --- a/slirp/socket.c
> +++ b/slirp/socket.c
> @@ -552,7 +552,8 @@ sosendto(struct socket *so, struct mbuf *m)
> slirp->vnetwork_addr.s_addr) {
> /* It's an alias */
> if (so->so_faddr.s_addr == slirp->vnameserver_addr.s_addr) {
> - addr.sin_addr = dns_addr;
> + if (get_dns_addr(&addr.sin_addr) < 0)
> + addr.sin_addr = loopback_addr;
> } else {
> addr.sin_addr = loopback_addr;
> }
> diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
> index 51b3834..0417345 100644
> --- a/slirp/tcp_subr.c
> +++ b/slirp/tcp_subr.c
> @@ -340,7 +340,8 @@ int tcp_fconnect(struct socket *so)
> slirp->vnetwork_addr.s_addr) {
> /* It's an alias */
> if (so->so_faddr.s_addr == slirp->vnameserver_addr.s_addr) {
> - addr.sin_addr = dns_addr;
> + if (get_dns_addr(&addr.sin_addr) < 0)
> + addr.sin_addr = loopback_addr;
> } else {
> addr.sin_addr = loopback_addr;
> }
>
>
>
- Re: [Qemu-devel] [PATCH] slirp: Read host DNS config on demand,
Michael S. Tsirkin <=