add vfu_get_poll_fd() (#322)

Library users can use this to sleep on either a newly-attached socket client, or
a new message.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@nutanix.com>

4 files changed, 113 insertions, 81 deletions

diff --git a/include/libvfio-user.h b/include/libvfio-user.h
index 11666d0..68307cb 100644
--- a/include/libvfio-user.h
+++ b/include/libvfio-user.h
@@ -130,6 +130,13 @@ int
 vfu_attach_ctx(vfu_ctx_t *vfu_ctx);
 
 /**
+ * Return a file descriptor suitable for waiting on via epoll() or similar. This
+ * should not be cached, as it may change after a successful vfu_attach_ctx().
+ */
+int
+vfu_get_poll_fd(vfu_ctx_t *vfu_ctx);
+
+/**
  * Polls the vfu_ctx and processes the command recieved from client.
  * - Blocking vfu_ctx:
  *   Blocks until new request is received from client and continues processing
diff --git a/lib/libvfio-user.c b/lib/libvfio-user.c
index 738d3b7..2dccd62 100644
--- a/lib/libvfio-user.c
+++ b/lib/libvfio-user.c
@@ -1111,15 +1111,6 @@ vfu_get_private(vfu_ctx_t *vfu_ctx)
     return vfu_ctx->pvt;
 }
 
-int
-vfu_attach_ctx(vfu_ctx_t *vfu_ctx)
-{
-
-    assert(vfu_ctx != NULL);
-
-    return vfu_ctx->tran->attach(vfu_ctx);
-}
-
 vfu_ctx_t *
 vfu_create_ctx(vfu_trans_t trans, const char *path, int flags, void *pvt,
                vfu_dev_type_t dev_type)
@@ -1197,6 +1188,24 @@ err_out:
 }
 
 int
+vfu_attach_ctx(vfu_ctx_t *vfu_ctx)
+{
+
+    assert(vfu_ctx != NULL);
+
+    return vfu_ctx->tran->attach(vfu_ctx);
+}
+
+int
+vfu_get_poll_fd(vfu_ctx_t *vfu_ctx)
+{
+
+    assert(vfu_ctx != NULL);
+
+    return vfu_ctx->tran->get_poll_fd(vfu_ctx);
+}
+
+int
 vfu_setup_log(vfu_ctx_t *vfu_ctx, vfu_log_fn_t *log, int log_level)
 {
 
diff --git a/lib/private.h b/lib/private.h
index 5ea25be..787cae9 100644
--- a/lib/private.h
+++ b/lib/private.h
@@ -52,6 +52,9 @@ ERROR_PTR(int err)
 
 struct transport_ops {
     int (*init)(vfu_ctx_t *vfu_ctx);
+
+    int (*get_poll_fd)(vfu_ctx_t *vfu_ctx);
+
     int (*attach)(vfu_ctx_t *vfu_ctx);
 
     int (*get_request)(vfu_ctx_t *vfu_ctx, struct vfio_user_header *hdr,
diff --git a/lib/tran_sock.c b/lib/tran_sock.c
index 4aa4ee0..419588d 100644
--- a/lib/tran_sock.c
+++ b/lib/tran_sock.c
@@ -56,78 +56,6 @@ typedef struct {
     int conn_fd;
 } tran_sock_t;
 
-static int
-tran_sock_init(vfu_ctx_t *vfu_ctx)
-{
-    struct sockaddr_un addr = { .sun_family = AF_UNIX };
-    tran_sock_t *ts = NULL;
-    mode_t mode;
-    int ret;
-
-    assert(vfu_ctx != NULL);
-
-    /* FIXME SPDK can't easily run as non-root */
-    mode = umask(0000);
-
-    ts = calloc(1, sizeof(tran_sock_t));
-
-    if (ts == NULL) {
-        ret = -errno;
-        goto out;
-    }
-
-    ts->listen_fd = -1;
-    ts->conn_fd = -1;
-
-    if ((ts->listen_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
-	    ret = -errno;
-        goto out;
-    }
-
-    if (vfu_ctx->flags & LIBVFIO_USER_FLAG_ATTACH_NB) {
-        ret = fcntl(ts->listen_fd, F_SETFL,
-                    fcntl(ts->listen_fd, F_GETFL, 0) | O_NONBLOCK);
-        if (ret < 0) {
-            ret = -errno;
-            goto out;
-        }
-    }
-
-    ret = snprintf(addr.sun_path, sizeof addr.sun_path, "%s", vfu_ctx->uuid);
-    if (ret >= (int)sizeof(addr.sun_path)) {
-        ret = -ENAMETOOLONG;
-    }
-    if (ret < 0) {
-        goto out;
-    }
-
-    /* start listening business */
-    ret = bind(ts->listen_fd, (struct sockaddr *)&addr, sizeof(addr));
-    if (ret < 0) {
-	    ret = -errno;
-        goto out;
-    }
-
-    ret = listen(ts->listen_fd, 0);
-    if (ret < 0) {
-        ret = -errno;
-    }
-
-out:
-    umask(mode);
-
-    if (ret != 0) {
-        if (ts->listen_fd != -1) {
-            close(ts->listen_fd);
-        }
-        free(ts);
-        return ret;
-    }
-
-    vfu_ctx->tran_data = ts;
-    return 0;
-}
-
 int
 tran_sock_send_iovec(int sock, uint16_t msg_id, bool is_reply,
                      enum vfio_user_command cmd,
@@ -444,6 +372,90 @@ tran_sock_msg(int sock, uint16_t msg_id, enum vfio_user_command cmd,
                              recv_data, recv_len, NULL, NULL);
 }
 
+static int
+tran_sock_init(vfu_ctx_t *vfu_ctx)
+{
+    struct sockaddr_un addr = { .sun_family = AF_UNIX };
+    tran_sock_t *ts = NULL;
+    mode_t mode;
+    int ret;
+
+    assert(vfu_ctx != NULL);
+
+    /* FIXME SPDK can't easily run as non-root */
+    mode = umask(0000);
+
+    ts = calloc(1, sizeof(tran_sock_t));
+
+    if (ts == NULL) {
+        ret = -errno;
+        goto out;
+    }
+
+    ts->listen_fd = -1;
+    ts->conn_fd = -1;
+
+    if ((ts->listen_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
+        ret = -errno;
+        goto out;
+    }
+
+    if (vfu_ctx->flags & LIBVFIO_USER_FLAG_ATTACH_NB) {
+        ret = fcntl(ts->listen_fd, F_SETFL,
+                    fcntl(ts->listen_fd, F_GETFL, 0) | O_NONBLOCK);
+        if (ret < 0) {
+            ret = -errno;
+            goto out;
+        }
+    }
+
+    ret = snprintf(addr.sun_path, sizeof addr.sun_path, "%s", vfu_ctx->uuid);
+    if (ret >= (int)sizeof(addr.sun_path)) {
+        ret = -ENAMETOOLONG;
+    }
+    if (ret < 0) {
+        goto out;
+    }
+
+    /* start listening business */
+    ret = bind(ts->listen_fd, (struct sockaddr *)&addr, sizeof(addr));
+    if (ret < 0) {
+        ret = -errno;
+        goto out;
+    }
+
+    ret = listen(ts->listen_fd, 0);
+    if (ret < 0) {
+        ret = -errno;
+    }
+
+out:
+    umask(mode);
+
+    if (ret != 0) {
+        if (ts->listen_fd != -1) {
+            close(ts->listen_fd);
+        }
+        free(ts);
+        return ret;
+    }
+
+    vfu_ctx->tran_data = ts;
+    return 0;
+}
+
+int
+tran_sock_get_poll_fd(vfu_ctx_t *vfu_ctx)
+{
+    tran_sock_t *ts = vfu_ctx->tran_data;
+
+    if (ts->conn_fd != -1) {
+        return ts->conn_fd;
+    }
+
+    return ts->listen_fd;
+}
+
 /*
  * Expected JSON is of the form:
  *
@@ -857,6 +869,7 @@ tran_sock_fini(vfu_ctx_t *vfu_ctx)
 
 struct transport_ops tran_sock_ops = {
     .init = tran_sock_init,
+    .get_poll_fd = tran_sock_get_poll_fd,
     .attach = tran_sock_attach,
     .get_request = tran_sock_get_request,
     .recv_body = tran_sock_recv_body,