[PATCH RFC 1/4] tools/xenstore: simplify xenstored main loop

[Juergen Gross <jgross@xxxxxxxx>]

The main loop of xenstored is rather complicated due to different
handling of socket and ring-page interfaces. Unify that handling by
introducing interface type specific functions can_read() and
can_write().

Put the interface type specific functions in an own structure and let
struct connection contain only a pointer to that new function vector.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 tools/xenstore/xenstored_core.c   | 118 +++++++++++++++++-------------
 tools/xenstore/xenstored_core.h   |  16 ++--
 tools/xenstore/xenstored_domain.c |  11 ++-
 3 files changed, 85 insertions(+), 60 deletions(-)

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 65ecdd0568..c89f5202fe 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -226,8 +226,8 @@ static bool write_messages(struct connection *conn)
                                sockmsg_string(out->hdr.msg.type),
                                out->hdr.msg.len,
                                out->buffer, conn);
-               ret = conn->write(conn, out->hdr.raw + out->used,
-                                 sizeof(out->hdr) - out->used);
+               ret = conn->funcs->write(conn, out->hdr.raw + out->used,
+                                        sizeof(out->hdr) - out->used);
                if (ret < 0)
                        return false;
 
@@ -243,8 +243,8 @@ static bool write_messages(struct connection *conn)
                        return true;
        }
 
-       ret = conn->write(conn, out->buffer + out->used,
-                         out->hdr.msg.len - out->used);
+       ret = conn->funcs->write(conn, out->buffer + out->used,
+                                out->hdr.msg.len - out->used);
        if (ret < 0)
                return false;
 
@@ -1520,8 +1520,8 @@ static void handle_input(struct connection *conn)
        /* Not finished header yet? */
        if (in->inhdr) {
                if (in->used != sizeof(in->hdr)) {
-                       bytes = conn->read(conn, in->hdr.raw + in->used,
-                                          sizeof(in->hdr) - in->used);
+                       bytes = conn->funcs->read(conn, in->hdr.raw + in->used,
+                                                 sizeof(in->hdr) - in->used);
                        if (bytes < 0)
                                goto bad_client;
                        in->used += bytes;
@@ -1546,8 +1546,8 @@ static void handle_input(struct connection *conn)
                in->inhdr = false;
        }
 
-       bytes = conn->read(conn, in->buffer + in->used,
-                          in->hdr.msg.len - in->used);
+       bytes = conn->funcs->read(conn, in->buffer + in->used,
+                                 in->hdr.msg.len - in->used);
        if (bytes < 0)
                goto bad_client;
 
@@ -1570,7 +1570,7 @@ static void handle_output(struct connection *conn)
                ignore_connection(conn);
 }
 
-struct connection *new_connection(connwritefn_t *write, connreadfn_t *read)
+struct connection *new_connection(struct interface_funcs *funcs)
 {
        struct connection *new;
 
@@ -1580,8 +1580,7 @@ struct connection *new_connection(connwritefn_t *write, 
connreadfn_t *read)
 
        new->fd = -1;
        new->pollfd_idx = -1;
-       new->write = write;
-       new->read = read;
+       new->funcs = funcs;
        new->is_ignored = false;
        new->transaction_started = 0;
        INIT_LIST_HEAD(&new->out_list);
@@ -1622,6 +1621,16 @@ int readfd(struct connection *conn, void *data, unsigned 
int len)
        errno = EBADF;
        return -1;
 }
+
+static bool socket_can_write(struct connection *conn)
+{
+       return false;
+}
+
+static bool socket_can_read(struct connection *conn)
+{
+       return false;
+}
 #else
 int writefd(struct connection *conn, const void *data, unsigned int len)
 {
@@ -1661,6 +1670,32 @@ int readfd(struct connection *conn, void *data, unsigned 
int len)
        return rc;
 }
 
+static bool socket_can_write(struct connection *conn)
+{
+       if (conn->pollfd_idx == -1)
+               return false;
+
+       if (fds[conn->pollfd_idx].revents & ~(POLLIN | POLLOUT)) {
+               talloc_free(conn);
+               return false;
+       }
+
+       return fds[conn->pollfd_idx].revents & POLLOUT;
+}
+
+static bool socket_can_read(struct connection *conn)
+{
+       if (conn->pollfd_idx == -1)
+               return false;
+
+       if (fds[conn->pollfd_idx].revents & ~(POLLIN | POLLOUT)) {
+               talloc_free(conn);
+               return false;
+       }
+
+       return fds[conn->pollfd_idx].revents & POLLIN;
+}
+
 static void accept_connection(int sock)
 {
        int fd;
@@ -1670,7 +1705,7 @@ static void accept_connection(int sock)
        if (fd < 0)
                return;
 
-       conn = new_connection(writefd, readfd);
+       conn = new_connection(&socket_funcs);
        if (conn)
                conn->fd = fd;
        else
@@ -1678,6 +1713,13 @@ static void accept_connection(int sock)
 }
 #endif
 
+struct interface_funcs socket_funcs = {
+       .write = writefd,
+       .read = readfd,
+       .can_write = socket_can_write,
+       .can_read = socket_can_read,
+};
+
 static int tdb_flags;
 
 /* We create initial nodes manually. */
@@ -2280,47 +2322,19 @@ int main(int argc, char *argv[])
                        if (&next->list != &connections)
                                talloc_increase_ref_count(next);
 
-                       if (conn->domain) {
-                               if (domain_can_read(conn))
-                                       handle_input(conn);
-                               if (talloc_free(conn) == 0)
-                                       continue;
-
-                               talloc_increase_ref_count(conn);
-                               if (domain_can_write(conn) &&
-                                   !list_empty(&conn->out_list))
-                                       handle_output(conn);
-                               if (talloc_free(conn) == 0)
-                                       continue;
-                       } else {
-                               if (conn->pollfd_idx != -1) {
-                                       if (fds[conn->pollfd_idx].revents
-                                           & ~(POLLIN|POLLOUT))
-                                               talloc_free(conn);
-                                       else if ((fds[conn->pollfd_idx].revents
-                                                 & POLLIN) &&
-                                                !conn->is_ignored)
-                                               handle_input(conn);
-                               }
-                               if (talloc_free(conn) == 0)
-                                       continue;
-
-                               talloc_increase_ref_count(conn);
-
-                               if (conn->pollfd_idx != -1) {
-                                       if (fds[conn->pollfd_idx].revents
-                                           & ~(POLLIN|POLLOUT))
-                                               talloc_free(conn);
-                                       else if ((fds[conn->pollfd_idx].revents
-                                                 & POLLOUT) &&
-                                                !conn->is_ignored)
-                                               handle_output(conn);
-                               }
-                               if (talloc_free(conn) == 0)
-                                       continue;
+                       if (conn->funcs->can_read(conn))
+                               handle_input(conn);
+                       if (talloc_free(conn) == 0)
+                               continue;
 
-                               conn->pollfd_idx = -1;
-                       }
+                       talloc_increase_ref_count(conn);
+
+                       if (conn->funcs->can_write(conn))
+                               handle_output(conn);
+                       if (talloc_free(conn) == 0)
+                               continue;
+
+                       conn->pollfd_idx = -1;
                }
 
                if (delayed_requests) {
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index 589699e833..84b364d82c 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -87,8 +87,13 @@ struct delayed_request {
 };
 
 struct connection;
-typedef int connwritefn_t(struct connection *, const void *, unsigned int);
-typedef int connreadfn_t(struct connection *, void *, unsigned int);
+
+struct interface_funcs {
+       int (*write)(struct connection *, const void *, unsigned int);
+       int (*read)(struct connection *, void *, unsigned int);
+       bool (*can_write)(struct connection *);
+       bool (*can_read)(struct connection *);
+};
 
 struct connection
 {
@@ -132,9 +137,8 @@ struct connection
        /* My watches. */
        struct list_head watches;
 
-       /* Methods for communicating over this connection: write can be NULL */
-       connwritefn_t *write;
-       connreadfn_t *read;
+       /* Methods for communicating over this connection. */
+       struct interface_funcs *funcs;
 
        /* Support for live update: connection id. */
        unsigned int conn_id;
@@ -197,7 +201,7 @@ int write_node_raw(struct connection *conn, TDB_DATA *key, 
struct node *node,
 struct node *read_node(struct connection *conn, const void *ctx,
                       const char *name);
 
-struct connection *new_connection(connwritefn_t *write, connreadfn_t *read);
+struct connection *new_connection(struct interface_funcs *funcs);
 struct connection *get_connection_by_id(unsigned int conn_id);
 void check_store(void);
 void corrupt(struct connection *conn, const char *fmt, ...);
diff --git a/tools/xenstore/xenstored_domain.c 
b/tools/xenstore/xenstored_domain.c
index 3d4d0649a2..04f2a974e4 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -172,6 +172,13 @@ static int readchn(struct connection *conn, void *data, 
unsigned int len)
        return len;
 }
 
+static struct interface_funcs domain_funcs = {
+       .write = writechn,
+       .read = readchn,
+       .can_write = domain_can_write,
+       .can_read = domain_can_read,
+};
+
 static void *map_interface(domid_t domid)
 {
        return xengnttab_map_grant_ref(*xgt_handle, domid,
@@ -389,7 +396,7 @@ static int new_domain(struct domain *domain, int port, bool 
restore)
 
        domain->introduced = true;
 
-       domain->conn = new_connection(writechn, readchn);
+       domain->conn = new_connection(&domain_funcs);
        if (!domain->conn)  {
                errno = ENOMEM;
                return errno;
@@ -1288,7 +1295,7 @@ void read_state_connection(const void *ctx, const void 
*state)
        struct domain *domain, *tdomain;
 
        if (sc->conn_type == XS_STATE_CONN_TYPE_SOCKET) {
-               conn = new_connection(writefd, readfd);
+               conn = new_connection(&socket_funcs);
                if (!conn)
                        barf("error restoring connection");
                conn->fd = sc->spec.socket_fd;
-- 
2.26.2