Xen regression fixes and cleanups

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Merge tag 'pull-xenfv-20250116' of git://git.infradead.org/users/dwmw2/qemu into staging

Xen regression fixes and cleanups

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* tag 'pull-xenfv-20250116' of git://git.infradead.org/users/dwmw2/qemu:
  system/runstate: Fix regression, clarify BQL status of exit notifiers
  hw/xen: Fix errp handling in xen_console
  hw/xen: Use xs_node_read() from xenstore_read_str() instead of open-coding it
  hw/xen: Use xs_node_read() from xen_netdev_get_name()
  hw/xen: Use xs_node_read() from xen_console_get_name()
  hw/xen: Use xs_node_read() from xs_node_vscanf()
  xen: do not use '%ms' scanf specifier
  hw/xen: Add xs_node_read() helper function

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/block/xen-block.c

@@ -239,7 +239,8 @@ static void xen_block_connect(XenDevice *xendev, Error **errp)
         return;
     }
 
-    if (xen_device_frontend_scanf(xendev, "protocol", "%ms", &str) != 1) {
+    str = xen_device_frontend_read(xendev, "protocol");
+    if (!str) {
         /* x86 defaults to the 32-bit protocol even for 64-bit guests. */
         if (object_dynamic_cast(OBJECT(qdev_get_machine()), "x86-machine")) {
             protocol = BLKIF_PROTOCOL_X86_32;

hw/char/xen_console.c

@@ -367,28 +367,28 @@ static char *xen_console_get_name(XenDevice *xendev, Error **errp)
 
     if (con->dev == -1) {
         XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
-        char fe_path[XENSTORE_ABS_PATH_MAX + 1];
         int idx = (xen_mode == XEN_EMULATE) ? 0 : 1;
+        Error *local_err = NULL;
         char *value;
 
         /* Theoretically we could go up to INT_MAX here but that's overkill */
         while (idx < 100) {
             if (!idx) {
-                snprintf(fe_path, sizeof(fe_path),
+                value = xs_node_read(xenbus->xsh, XBT_NULL, NULL, &local_err,
-                         "/local/domain/%u/console", xendev->frontend_id);
+                                     "/local/domain/%u/console",
+                                     xendev->frontend_id);
             } else {
-                snprintf(fe_path, sizeof(fe_path),
+                value = xs_node_read(xenbus->xsh, XBT_NULL, NULL, &local_err,
                                      "/local/domain/%u/device/console/%u",
                                      xendev->frontend_id, idx);
             }
-            value = qemu_xen_xs_read(xenbus->xsh, XBT_NULL, fe_path, NULL);
             if (!value) {
                 if (errno == ENOENT) {
                     con->dev = idx;
+                    error_free(local_err);
                     goto found;
                 }
-                error_setg(errp, "cannot read %s: %s", fe_path,
+                error_propagate(errp, local_err);
-                           strerror(errno));
                 return NULL;
             }
             free(value);
@@ -550,7 +550,8 @@ static void xen_console_device_create(XenBackendInstance *backend,
         goto fail;
     }
 
-    if (xs_node_scanf(xsh, XBT_NULL, fe, "type", errp, "%ms", &type) != 1) {
+    type = xs_node_read(xsh, XBT_NULL, NULL, errp, "%s/%s", fe, "type");
+    if (!type) {
         error_prepend(errp, "failed to read console device type: ");
         goto fail;
     }
@@ -568,7 +569,8 @@ static void xen_console_device_create(XenBackendInstance *backend,
 
     snprintf(label, sizeof(label), "xencons%ld", number);
 
-    if (xs_node_scanf(xsh, XBT_NULL, fe, "output", NULL, "%ms", &output) == 1) {
+    output = xs_node_read(xsh, XBT_NULL, NULL, errp, "%s/%s", fe, "output");
+    if (output) {
         /*
          * FIXME: sure we want to support implicit
          * muxed monitors here?
@@ -579,10 +581,17 @@ static void xen_console_device_create(XenBackendInstance *backend,
                        output);
             goto fail;
         }
-    } else if (number) {
+    } else if (errno != ENOENT) {
+        error_prepend(errp, "console: No valid chardev found: ");
+        goto fail;
+    } else {
+        error_free(*errp);
+        *errp = NULL;
+
+        if (number) {
             cd = serial_hd(number);
             if (!cd) {
-            error_prepend(errp, "console: No serial device #%ld found: ",
+                error_setg(errp, "console: No serial device #%ld found",
                            number);
                 goto fail;
             }
@@ -594,6 +603,7 @@ static void xen_console_device_create(XenBackendInstance *backend,
                 goto fail;
             }
         }
+    }
 
     if (!qemu_chr_fe_init(&con->chr, cd, errp)) {
         error_prepend(errp, "console: failed to initialize backing chardev: ");

hw/net/xen_nic.c

@@ -510,23 +510,22 @@ static char *xen_netdev_get_name(XenDevice *xendev, Error **errp)
 
     if (netdev->dev == -1) {
         XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
-        char fe_path[XENSTORE_ABS_PATH_MAX + 1];
         int idx = (xen_mode == XEN_EMULATE) ? 0 : 1;
+        Error *local_err = NULL;
         char *value;
 
         /* Theoretically we could go up to INT_MAX here but that's overkill */
         while (idx < 100) {
-            snprintf(fe_path, sizeof(fe_path),
+            value = xs_node_read(xenbus->xsh, XBT_NULL, NULL, &local_err,
                                  "/local/domain/%u/device/vif/%u",
                                  xendev->frontend_id, idx);
-            value = qemu_xen_xs_read(xenbus->xsh, XBT_NULL, fe_path, NULL);
             if (!value) {
                 if (errno == ENOENT) {
                     netdev->dev = idx;
+                    error_free(local_err);
                     goto found;
                 }
-                error_setg(errp, "cannot read %s: %s", fe_path,
+                error_propagate(errp, local_err);
-                           strerror(errno));
                 return NULL;
             }
             free(value);

hw/xen/trace-events

@@ -38,7 +38,7 @@ xen_device_remove_watch(const char *type, char *name, const char *node, const ch
 xs_node_create(const char *node) "%s"
 xs_node_destroy(const char *node) "%s"
 xs_node_vprintf(char *path, char *value) "%s %s"
-xs_node_vscanf(char *path, char *value) "%s %s"
+xs_node_read(const char *path, const char *value) "%s %s"
 xs_node_watch(char *path) "%s"
 xs_node_unwatch(char *path) "%s"
 

hw/xen/xen-bus-helper.c

@@ -105,25 +105,22 @@ int xs_node_vscanf(struct qemu_xs_handle *h,  xs_transaction_t tid,
                    const char *node, const char *key, Error **errp,
                    const char *fmt, va_list ap)
 {
-    char *path, *value;
+    char *value;
     int rc;
 
-    path = (strlen(node) != 0) ? g_strdup_printf("%s/%s", node, key) :
+    if (node && strlen(node) != 0) {
-        g_strdup(key);
+        value = xs_node_read(h, tid, NULL, errp, "%s/%s", node, key);
-    value = qemu_xen_xs_read(h, tid, path, NULL);
+    } else {
-
+        value = xs_node_read(h, tid, NULL, errp, "%s", key);
-    trace_xs_node_vscanf(path, value);
+    }
 
     if (value) {
         rc = vsscanf(value, fmt, ap);
     } else {
-        error_setg_errno(errp, errno, "failed to read from '%s'",
-                         path);
         rc = EOF;
     }
 
     free(value);
-    g_free(path);
 
     return rc;
 }
@@ -142,6 +139,28 @@ int xs_node_scanf(struct qemu_xs_handle *h,  xs_transaction_t tid,
     return rc;
 }
 
+char *xs_node_read(struct qemu_xs_handle *h, xs_transaction_t tid,
+                   unsigned int *len, Error **errp,
+                   const char *path_fmt, ...)
+{
+    char *path, *value;
+    va_list ap;
+
+    va_start(ap, path_fmt);
+    path = g_strdup_vprintf(path_fmt, ap);
+    va_end(ap);
+
+    value = qemu_xen_xs_read(h, tid, path, len);
+    trace_xs_node_read(path, value);
+    if (!value) {
+        error_setg_errno(errp, errno, "failed to read from '%s'", path);
+    }
+
+    g_free(path);
+
+    return value;
+}
+
 struct qemu_xs_watch *xs_node_watch(struct qemu_xs_handle *h, const char *node,
                                     const char *key, xs_watch_fn fn,
                                     void *opaque, Error **errp)

hw/xen/xen-bus.c

@@ -156,8 +156,8 @@ again:
             !strcmp(key[i], "hotplug-status"))
             continue;
 
-        if (xs_node_scanf(xenbus->xsh, tid, path, key[i], NULL, "%ms",
+        val = xs_node_read(xenbus->xsh, tid, NULL, NULL, "%s/%s", path, key[i]);
-                          &val) == 1) {
+        if (val) {
             qdict_put_str(opts, key[i], val);
             free(val);
         }
@@ -650,6 +650,16 @@ int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
     return rc;
 }
 
+char *xen_device_frontend_read(XenDevice *xendev, const char *key)
+{
+    XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
+
+    g_assert(xenbus->xsh);
+
+    return xs_node_read(xenbus->xsh, XBT_NULL, NULL, NULL, "%s/%s",
+                        xendev->frontend_path, key);
+}
+
 static void xen_device_frontend_set_state(XenDevice *xendev,
                                           enum xenbus_state state,
                                           bool publish)

hw/xen/xen_pvdev.c

@@ -22,6 +22,7 @@
 #include "qemu/main-loop.h"
 #include "hw/qdev-core.h"
 #include "hw/xen/xen-legacy-backend.h"
+#include "hw/xen/xen-bus-helper.h"
 #include "hw/xen/xen_pvdev.h"
 
 /* private */
@@ -81,12 +82,9 @@ int xenstore_write_str(const char *base, const char *node, const char *val)
 
 char *xenstore_read_str(const char *base, const char *node)
 {
-    char abspath[XEN_BUFSIZE];
-    unsigned int len;
     char *str, *ret = NULL;
 
-    snprintf(abspath, sizeof(abspath), "%s/%s", base, node);
+    str = xs_node_read(xenstore, 0, NULL, NULL, "%s/%s", base, node);
-    str = qemu_xen_xs_read(xenstore, 0, abspath, &len);
     if (str != NULL) {
         /* move to qemu-allocated memory to make sure
          * callers can safely g_free() stuff. */

include/hw/xen/xen-bus-helper.h

@@ -38,6 +38,15 @@ int xs_node_scanf(struct qemu_xs_handle *h,  xs_transaction_t tid,
                   const char *fmt, ...)
     G_GNUC_SCANF(6, 7);
 
+/*
+ * Unlike other functions here, the printf-formatted path_fmt is for
+ * the XenStore path, not the contents of the node.
+ */
+char *xs_node_read(struct qemu_xs_handle *h, xs_transaction_t tid,
+                   unsigned int *len, Error **errp,
+                   const char *path_fmt, ...)
+    G_GNUC_PRINTF(5, 6);
+
 /* Watch node/key unless node is empty, in which case watch key */
 struct qemu_xs_watch *xs_node_watch(struct qemu_xs_handle *h, const char *node,
                                     const char *key, xs_watch_fn fn,

include/hw/xen/xen-bus.h

@@ -91,6 +91,7 @@ void xen_device_frontend_printf(XenDevice *xendev, const char *key,
 int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
                               const char *fmt, ...)
     G_GNUC_SCANF(3, 4);
+char *xen_device_frontend_read(XenDevice *xendev, const char *key);
 
 void xen_device_set_max_grant_refs(XenDevice *xendev, unsigned int nr_refs,
                                    Error **errp);

include/system/system.h

@@ -15,6 +15,7 @@ extern bool qemu_uuid_set;
 
 const char *qemu_get_vm_name(void);
 
+/* Exit notifiers will run with BQL held. */
 void qemu_add_exit_notifier(Notifier *notify);
 void qemu_remove_exit_notifier(Notifier *notify);
 

system/runstate.c

@@ -850,6 +850,7 @@ void qemu_remove_exit_notifier(Notifier *notify)
 
 static void qemu_run_exit_notifiers(void)
 {
+    BQL_LOCK_GUARD();
     notifier_list_notify(&exit_notifiers, NULL);
 }