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tcp: Improve handling of fallback if socket pool is empty on new splice

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When creating a new spliced connection, we need to get a socket in the
other ns from the originating one.  To avoid excessive ns switches we
usually get these from a pool refilled on a timer.  However, if the pool
runs out we need a fallback.  Currently that's done by passing -1 as the
socket to tcp_splice_connnect() and running it in the target ns.

This means that tcp_splice_connect() itself needs to have different cases
depending on whether it's given an existing socket or not, which is
a separate concern from what it's mostly doing.  We change it to require
a suitable open socket to be passed in, and ensuring in the caller that we
have one.

This requires adding the fallback paths to the caller, tcp_splice_new().
We use slightly different approaches for a socket in the init ns versus the
guest ns.

This also means that we no longer need to run tcp_splice_connect() itself
in the guest ns, which allows us to remove a bunch of boilerplate code.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-02-14 10:48:23 +11:00 committed by Stefano Brivio
parent dc467d526f
commit 6ccab72d9b
3 changed files with 31 additions and 59 deletions
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2
tcp.c
View file

@ -1882,7 +1882,7 @@ int tcp_conn_pool_sock(int pool[])
*
* Return: socket number on success, negative code if socket creation failed
*/
static int tcp_conn_new_sock(const struct ctx *c, sa_family_t af)
int tcp_conn_new_sock(const struct ctx *c, sa_family_t af)
{
int s;

1
tcp_conn.h
View file

@ -193,6 +193,7 @@ void tcp_table_compact(struct ctx *c, union tcp_conn *hole);
void tcp_splice_destroy(struct ctx *c, union tcp_conn *conn_union);
void tcp_splice_timer(struct ctx *c, union tcp_conn *conn_union);
int tcp_conn_pool_sock(int pool[]);
int tcp_conn_new_sock(const struct ctx *c, sa_family_t af);
void tcp_sock_refill_pool(const struct ctx *c, int pool[], int af);
void tcp_splice_refill(const struct ctx *c);

85
tcp_splice.c
View file

@ -87,6 +87,9 @@ static const char *tcp_splice_flag_str[] __attribute((__unused__)) = {
"RCVLOWAT_ACT_B", "CLOSING",
};
/* Forward declaration */
static int tcp_sock_refill_ns(void *arg);
/**
* tcp_splice_conn_epoll_events() - epoll events masks for given state
* @events: Connection event flags
@ -347,12 +350,8 @@ static int tcp_splice_connect_finish(const struct ctx *c,
* Return: 0 for connect() succeeded or in progress, negative value on error
*/
static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn,
int s, in_port_t port)
int sock_conn, in_port_t port)
{
int sock_conn = (s >= 0) ? s : socket(CONN_V6(conn) ? AF_INET6 :
AF_INET,
SOCK_STREAM | SOCK_NONBLOCK,
IPPROTO_TCP);
struct sockaddr_in6 addr6 = {
.sin6_family = AF_INET6,
.sin6_port = htons(port),
@ -366,19 +365,8 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn,
const struct sockaddr *sa;
socklen_t sl;
if (sock_conn < 0)
return -errno;
if (sock_conn > SOCKET_MAX) {
close(sock_conn);
return -EIO;
}
conn->b = sock_conn;
if (s < 0)
tcp_sock_set_bufsize(c, conn->b);
if (setsockopt(conn->b, SOL_TCP, TCP_QUICKACK,
&((int){ 1 }), sizeof(int))) {
trace("TCP (spliced): failed to set TCP_QUICKACK on socket %i",
@ -409,36 +397,6 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn,
return 0;
}
/**
* struct tcp_splice_connect_ns_arg - Arguments for tcp_splice_connect_ns()
* @c: Execution context
* @conn: Accepted inbound connection
* @port: Destination port, host order
* @ret: Return value of tcp_splice_connect_ns()
*/
struct tcp_splice_connect_ns_arg {
const struct ctx *c;
struct tcp_splice_conn *conn;
in_port_t port;
int ret;
};
/**
* tcp_splice_connect_ns() - Enter namespace and call tcp_splice_connect()
* @arg: See struct tcp_splice_connect_ns_arg
*
* Return: 0
*/
static int tcp_splice_connect_ns(void *arg)
{
struct tcp_splice_connect_ns_arg *a;
a = (struct tcp_splice_connect_ns_arg *)arg;
ns_enter(a->c);
a->ret = tcp_splice_connect(a->c, a->conn, -1, a->port);
return 0;
}
/**
* tcp_splice_new() - Handle new spliced connection
* @c: Execution context
@ -451,24 +409,37 @@ static int tcp_splice_connect_ns(void *arg)
static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
in_port_t port, int outbound)
{
int *p, s = -1;
int s = -1;
if (outbound)
p = CONN_V6(conn) ? init_sock_pool6 : init_sock_pool4;
else
p = CONN_V6(conn) ? ns_sock_pool6 : ns_sock_pool4;
/* If the pool is empty we take slightly different approaches
* for init or ns sockets. For init sockets we just open a
* new one without refilling the pool to keep latency down.
* For ns sockets, we're going to incur the latency of
* entering the ns anyway, so we might as well refill the
* pool.
*/
if (outbound) {
int *p = CONN_V6(conn) ? init_sock_pool6 : init_sock_pool4;
int af = CONN_V6(conn) ? AF_INET6 : AF_INET;
s = tcp_conn_pool_sock(p);
if (s < 0)
s = tcp_conn_new_sock(c, af);
} else {
int *p = CONN_V6(conn) ? ns_sock_pool6 : ns_sock_pool4;
/* No socket available in namespace: create a new one for connect() */
if (s < 0 && !outbound) {
struct tcp_splice_connect_ns_arg ns_arg = { c, conn, port, 0 };
/* If pool is empty, refill it first */
if (p[TCP_SOCK_POOL_SIZE-1] < 0)
NS_CALL(tcp_sock_refill_ns, c);
NS_CALL(tcp_splice_connect_ns, &ns_arg);
return ns_arg.ret;
s = tcp_conn_pool_sock(p);
}
if (s < 0) {
warn("Couldn't open connectable socket for splice (%d)", s);
return s;
}
/* Otherwise, the socket will connect on the side it was created on */
return tcp_splice_connect(c, conn, s, port);
}