[PATCH v3 1/7] xen: error handling and FreeBSD compatibility fixes

[PATCH v3 1/7] xen: error handling and FreeBSD compatibility fixes

[David Woodhouse]

Add a new xs_node_read() helper function which constructs the node path 
using a printf format string, and use it where appropriate.

In particular, use it to eliminate the use of the %ms format specifier 
for scanf(), which doesn't exist in FreeBSD.

v3:
 • Further cleanups using xs_node_read().
 • Clean up errp handling for xen-console 'output' node.
 • Improve comment for xs_node_read().

v2:
 • Add xs_node_read() helper.
 • Also fix usage of %ms in xen-block.c

David Woodhouse (6):
      hw/xen: Add xs_node_read() helper function
      hw/xen: Use xs_node_read() from xs_node_vscanf()
      hw/xen: Use xs_node_read() from xen_console_get_name()
      hw/xen: Use xs_node_read() from xen_netdev_get_name()
      hw/xen: Use xs_node_read() from xenstore_read_str() instead of open-coding it
      hw/xen: Fix errp handling in xen_console

Roger Pau Monné (1):
      xen: do not use '%ms' scanf specifier

 hw/block/xen-block.c            |  3 ++-
 hw/char/xen_console.c           | 56 ++++++++++++++++++++++++-----------------
 hw/net/xen_nic.c                | 13 +++++-----
 hw/xen/trace-events             |  2 +-
 hw/xen/xen-bus-helper.c         | 37 ++++++++++++++++++++-------
 hw/xen/xen-bus.c                | 14 +++++++++--
 hw/xen/xen_pvdev.c              |  6 ++---
 include/hw/xen/xen-bus-helper.h |  9 +++++++
 include/hw/xen/xen-bus.h        |  1 +
 9 files changed, 94 insertions(+), 47 deletions(-)

[PATCH v3 1/7] hw/xen: Add xs_node_read() helper function

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

This returns the full contents of the node, having created the node path
from the printf-style format string provided in its arguments.

This will save various callers from having to do so for themselves (and
from using xs_node_scanf() with the non-portable %ms format string.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
[remove double newline and constify trace parameters]
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 hw/xen/trace-events             |  1 +
 hw/xen/xen-bus-helper.c         | 22 ++++++++++++++++++++++
 include/hw/xen/xen-bus-helper.h |  9 +++++++++
 3 files changed, 32 insertions(+)

diff --git a/hw/xen/trace-events b/hw/xen/trace-events
index a07fe41c6d..461dee7b23 100644
--- a/hw/xen/trace-events
+++ b/hw/xen/trace-events
@@ -39,6 +39,7 @@ 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"
 
diff --git a/hw/xen/xen-bus-helper.c b/hw/xen/xen-bus-helper.c
index b2b2cc9c5d..22fd2f6c1a 100644
--- a/hw/xen/xen-bus-helper.c
+++ b/hw/xen/xen-bus-helper.c
@@ -142,6 +142,28 @@ 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)
diff --git a/include/hw/xen/xen-bus-helper.h b/include/hw/xen/xen-bus-helper.h
index d8dcc2f010..e9911115b3 100644
--- a/include/hw/xen/xen-bus-helper.h
+++ b/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,
-- 
2.47.0

Re: [PATCH v3 1/7] hw/xen: Add xs_node_read() helper function

[Anthony PERARD]

On Wed, Jan 15, 2025 at 04:27:19PM +0000, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> This returns the full contents of the node, having created the node path
> from the printf-style format string provided in its arguments.
> 
> This will save various callers from having to do so for themselves (and
> from using xs_node_scanf() with the non-portable %ms format string.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> [remove double newline and constify trace parameters]
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Thanks,

-- 
Anthony PERARD

[PATCH v3 2/7] xen: do not use '%ms' scanf specifier

[David Woodhouse]

From: Roger Pau Monne <roger.pau@citrix.com>

The 'm' parameter used to request auto-allocation of the destination variable
is not supported on FreeBSD, and as such leads to failures to parse.

What's more, the current usage of '%ms' with xs_node_scanf() is pointless, as
it just leads to a double allocation of the same string.  Instead use
xs_node_read() to read the whole xenstore node.

Fixes: a783f8ad4ec9 ('xen: add a mechanism to automatically create XenDevice-s...')
Fixes: 9b7737469080 ('hw/xen: update Xen console to XenDevice model')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 hw/block/xen-block.c     |  3 ++-
 hw/char/xen_console.c    |  6 ++++--
 hw/xen/xen-bus.c         | 14 ++++++++++++--
 include/hw/xen/xen-bus.h |  1 +
 4 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 306d38927c..034a18b70e 100644
--- a/hw/block/xen-block.c
+++ b/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;
diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index ef0c2912ef..cb39b21504 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -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, NULL, "%s/%s", fe, "output");
+    if (output) {
         /*
          * FIXME: sure we want to support implicit
          * muxed monitors here?
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index adfc4efad0..85b92cded4 100644
--- a/hw/xen/xen-bus.c
+++ b/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) == 1) {
+        val = xs_node_read(xenbus->xsh, tid, NULL, NULL, "%s/%s", path, key[i]);
+        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)
diff --git a/include/hw/xen/xen-bus.h b/include/hw/xen/xen-bus.h
index 38d40afa37..2adb2af839 100644
--- a/include/hw/xen/xen-bus.h
+++ b/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);
-- 
2.47.0

Re: [PATCH v3 2/7] xen: do not use '%ms' scanf specifier

[Anthony PERARD]

On Wed, Jan 15, 2025 at 04:27:20PM +0000, David Woodhouse wrote:
> From: Roger Pau Monne <roger.pau@citrix.com>
> 
> The 'm' parameter used to request auto-allocation of the destination variable
> is not supported on FreeBSD, and as such leads to failures to parse.
> 
> What's more, the current usage of '%ms' with xs_node_scanf() is pointless, as
> it just leads to a double allocation of the same string.  Instead use
> xs_node_read() to read the whole xenstore node.
> 
> Fixes: a783f8ad4ec9 ('xen: add a mechanism to automatically create XenDevice-s...')
> Fixes: 9b7737469080 ('hw/xen: update Xen console to XenDevice model')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Thanks,

-- 
Anthony PERARD

Re: [PATCH v3 2/7] xen: do not use '%ms' scanf specifier

[Andrew Cooper]

On 15/01/2025 4:27 pm, David Woodhouse wrote:
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> index adfc4efad0..85b92cded4 100644
> --- a/hw/xen/xen-bus.c
> +++ b/hw/xen/xen-bus.c
> @@ -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);;

Double ;;

~Andrew

[PATCH v3 3/7] hw/xen: Use xs_node_read() from xs_node_vscanf()

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

Reduce some duplication.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
---
 hw/xen/trace-events     |  1 -
 hw/xen/xen-bus-helper.c | 15 ++++++---------
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/hw/xen/trace-events b/hw/xen/trace-events
index 461dee7b23..b67942d07b 100644
--- a/hw/xen/trace-events
+++ b/hw/xen/trace-events
@@ -38,7 +38,6 @@ 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"
diff --git a/hw/xen/xen-bus-helper.c b/hw/xen/xen-bus-helper.c
index 22fd2f6c1a..288fad422b 100644
--- a/hw/xen/xen-bus-helper.c
+++ b/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) :
-        g_strdup(key);
-    value = qemu_xen_xs_read(h, tid, path, NULL);
-
-    trace_xs_node_vscanf(path, value);
+    if (node && strlen(node) != 0) {
+        value = xs_node_read(h, tid, NULL, errp, "%s/%s", node, key);
+    } else {
+        value = xs_node_read(h, tid, NULL, errp, "%s", key);
+    }
 
     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;
 }
-- 
2.47.0

[PATCH v3 4/7] hw/xen: Use xs_node_read() from xen_console_get_name()

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

Now that xs_node_read() can construct a node path, no need to open-code it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
---
 hw/char/xen_console.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index cb39b21504..e61902461b 100644
--- a/hw/char/xen_console.c
+++ b/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),
-                         "/local/domain/%u/console", xendev->frontend_id);
+                value = xs_node_read(xenbus->xsh, XBT_NULL, NULL, &local_err,
+                                     "/local/domain/%u/console",
+                                     xendev->frontend_id);
             } else {
-                snprintf(fe_path, sizeof(fe_path),
-                         "/local/domain/%u/device/console/%u",
-                         xendev->frontend_id, idx);
+                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,
-                           strerror(errno));
+                error_propagate(errp, local_err);
                 return NULL;
             }
             free(value);
-- 
2.47.0

[PATCH v3 5/7] hw/xen: Use xs_node_read() from xen_netdev_get_name()

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

Now that xs_node_read() can construct a node path, no need to open-code it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
---
 hw/net/xen_nic.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/hw/net/xen_nic.c b/hw/net/xen_nic.c
index 97ebd9fa30..5410039490 100644
--- a/hw/net/xen_nic.c
+++ b/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),
-                     "/local/domain/%u/device/vif/%u",
-                     xendev->frontend_id, idx);
-            value = qemu_xen_xs_read(xenbus->xsh, XBT_NULL, fe_path, NULL);
+            value = xs_node_read(xenbus->xsh, XBT_NULL, NULL, &local_err,
+                                 "/local/domain/%u/device/vif/%u",
+                                 xendev->frontend_id, idx);
             if (!value) {
                 if (errno == ENOENT) {
                     netdev->dev = idx;
+                    error_free(local_err);
                     goto found;
                 }
-                error_setg(errp, "cannot read %s: %s", fe_path,
-                           strerror(errno));
+                error_propagate(errp, local_err);
                 return NULL;
             }
             free(value);
-- 
2.47.0

[PATCH v3 6/7] hw/xen: Use xs_node_read() from xenstore_read_str() instead of open-coding it

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
---
 hw/xen/xen_pvdev.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/hw/xen/xen_pvdev.c b/hw/xen/xen_pvdev.c
index c5ad71e8dc..c9143ba259 100644
--- a/hw/xen/xen_pvdev.c
+++ b/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 = qemu_xen_xs_read(xenstore, 0, abspath, &len);
+    str = xs_node_read(xenstore, 0, NULL, NULL, "%s/%s", base, node);
     if (str != NULL) {
         /* move to qemu-allocated memory to make sure
          * callers can safely g_free() stuff. */
-- 
2.47.0

[PATCH v3 7/7] hw/xen: Fix errp handling in xen_console

[David Woodhouse]

From: David Woodhouse <dwmw@amazon.co.uk>

When attempting to read the 'output' node, interpret any error *other*
than ENOENT as a fatal error. For ENOENT, fall back to serial_hd() to
find a character device, or create a null device.

Do not attempt to prepend to errp when serial_hd() fails; the error
isn't relevant (and prior to this change, wasn't set anyway).

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 hw/char/xen_console.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index e61902461b..9e7f6da343 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -569,7 +569,7 @@ static void xen_console_device_create(XenBackendInstance *backend,
 
     snprintf(label, sizeof(label), "xencons%ld", number);
 
-    output = xs_node_read(xsh, XBT_NULL, NULL, NULL, "%s/%s", fe, "output");
+    output = xs_node_read(xsh, XBT_NULL, NULL, errp, "%s/%s", fe, "output");
     if (output) {
         /*
          * FIXME: sure we want to support implicit
@@ -581,19 +581,27 @@ static void xen_console_device_create(XenBackendInstance *backend,
                        output);
             goto fail;
         }
-    } else if (number) {
-        cd = serial_hd(number);
-        if (!cd) {
-            error_prepend(errp, "console: No serial device #%ld found: ",
-                          number);
-            goto fail;
-        }
+    } else if (errno != ENOENT) {
+        error_prepend(errp, "console: No valid chardev found: ");
+        goto fail;
     } else {
-        /* No 'output' node on primary console: use null. */
-        cd = qemu_chr_new(label, "null", NULL);
-        if (!cd) {
-            error_setg(errp, "console: failed to create null device");
-            goto fail;
+        if (errp) {
+            error_free(*errp);
+        }
+        if (number) {
+            cd = serial_hd(number);
+            if (!cd) {
+                error_setg(errp, "console: No serial device #%ld found: ",
+                           number);
+                goto fail;
+            }
+        } else {
+            /* No 'output' node on primary console: use null. */
+            cd = qemu_chr_new(label, "null", NULL);
+            if (!cd) {
+                error_setg(errp, "console: failed to create null device");
+                goto fail;
+            }
         }
     }
 
-- 
2.47.0

Re: [PATCH v3 7/7] hw/xen: Fix errp handling in xen_console

[Anthony PERARD]

On Wed, Jan 15, 2025 at 04:27:25PM +0000, David Woodhouse wrote:
> diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
> index e61902461b..9e7f6da343 100644
> --- a/hw/char/xen_console.c
> +++ b/hw/char/xen_console.c
> @@ -581,19 +581,27 @@ static void xen_console_device_create(XenBackendInstance *backend,
>                         output);
>              goto fail;
>          }
> -    } else if (number) {
> -        cd = serial_hd(number);
> -        if (!cd) {
> -            error_prepend(errp, "console: No serial device #%ld found: ",
> -                          number);
> -            goto fail;
> -        }
> +    } else if (errno != ENOENT) {
> +        error_prepend(errp, "console: No valid chardev found: ");
> +        goto fail;
>      } else {
> -        /* No 'output' node on primary console: use null. */
> -        cd = qemu_chr_new(label, "null", NULL);
> -        if (!cd) {
> -            error_setg(errp, "console: failed to create null device");
> -            goto fail;
> +        if (errp) {

I don't think you need this check, with ERRP_GUARD() macro `errp` is
never NULL.

> +            error_free(*errp);

After this, I think you still need
    *errp = NULL;

> +        }
> +        if (number) {
> +            cd = serial_hd(number);
> +            if (!cd) {
> +                error_setg(errp, "console: No serial device #%ld found: ",

That error message doesn't need the ": " at the end anymore.

With those fixed: Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Cheers,

-- 
Anthony PERARD

Re: [PATCH v3 7/7] hw/xen: Fix errp handling in xen_console

[David Woodhouse]

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On Wed, 2025-01-15 at 17:49 +0100, Anthony PERARD wrote:
> 
> With those fixed: Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Thanks. I've pushed those changes and am watching the pipeline at
https://gitlab.com/dwmw2/qemu/-/pipelines/1626804720

I'll probably send a pull request tomorrow. The patch now looks like
this:

From 8b44a3e39f36540818d99ef8cf79e64bba1ed9c3 Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Wed, 15 Jan 2025 15:46:06 +0000
Subject: [PATCH] hw/xen: Fix errp handling in xen_console

When attempting to read the 'output' node, interpret any error *other*
than ENOENT as a fatal error. For ENOENT, fall back to serial_hd() to
find a character device, or create a null device.

Do not attempt to prepend to errp when serial_hd() fails; the error
isn't relevant (and prior to this change, wasn't set anyway).

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>
---
 hw/char/xen_console.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index e61902461b..d03c188d1d 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -569,7 +569,7 @@ static void xen_console_device_create(XenBackendInstance *backend,
 
     snprintf(label, sizeof(label), "xencons%ld", number);
 
-    output = xs_node_read(xsh, XBT_NULL, NULL, NULL, "%s/%s", fe, "output");
+    output = xs_node_read(xsh, XBT_NULL, NULL, errp, "%s/%s", fe, "output");
     if (output) {
         /*
          * FIXME: sure we want to support implicit
@@ -581,19 +581,27 @@ static void xen_console_device_create(XenBackendInstance *backend,
                        output);
             goto fail;
         }
-    } else if (number) {
-        cd = serial_hd(number);
-        if (!cd) {
-            error_prepend(errp, "console: No serial device #%ld found: ",
-                          number);
-            goto fail;
-        }
+    } else if (errno != ENOENT) {
+        error_prepend(errp, "console: No valid chardev found: ");
+        goto fail;
     } else {
-        /* No 'output' node on primary console: use null. */
-        cd = qemu_chr_new(label, "null", NULL);
-        if (!cd) {
-            error_setg(errp, "console: failed to create null device");
-            goto fail;
+        error_free(*errp);
+        *errp = NULL;
+
+        if (number) {
+            cd = serial_hd(number);
+            if (!cd) {
+                error_setg(errp, "console: No serial device #%ld found",
+                           number);
+                goto fail;
+            }
+        } else {
+            /* No 'output' node on primary console: use null. */
+            cd = qemu_chr_new(label, "null", NULL);
+            if (!cd) {
+                error_setg(errp, "console: failed to create null device");
+                goto fail;
+            }
         }
     }
 
-- 
2.47.0



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