git: 3cbf6473fa1c - stable/15 - bus: Add device_has_children predicate
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Date: Fri, 05 Dec 2025 15:09:06 UTC
The branch stable/15 has been updated by des:
URL: https://cgit.FreeBSD.org/src/commit/?id=3cbf6473fa1c3ca112d8fea343a0ebd693d10f06
commit 3cbf6473fa1c3ca112d8fea343a0ebd693d10f06
Author: Dag-Erling Smørgrav <des@FreeBSD.org>
AuthorDate: 2025-11-28 09:14:31 +0000
Commit: Dag-Erling Smørgrav <des@FreeBSD.org>
CommitDate: 2025-12-05 15:08:55 +0000
bus: Add device_has_children predicate
Add a device_has_children() function which can be used to check if a
device has children without allocating a list of them which we aren't
going to use, or even counting them.
Also modify device_get_children() so it can be used to query the count
without allocating a list.
MFC after: 1 week
Sponsored by: Klara, Inc.
Sponsored by: NetApp, Inc.
Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D53918
(cherry picked from commit 330d4437f2100fc05e576763f4f6a7198080663a)
---
share/man/man9/Makefile | 1 +
share/man/man9/device_get_children.9 | 47 ++++++++++++++++++++++++++++++------
sys/kern/subr_bus.c | 18 ++++++++++++++
sys/sys/bus.h | 1 +
4 files changed, 59 insertions(+), 8 deletions(-)
diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index bdf85363c8e1..11557907d5fe 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -1040,6 +1040,7 @@ MLINKS+=devfs_set_cdevpriv.9 devfs_clear_cdevpriv.9 \
MLINKS+=device_add_child.9 device_add_child_ordered.9
MLINKS+=device_enable.9 device_disable.9 \
device_enable.9 device_is_enabled.9
+MLINKS+=device_get_children.9 device_has_children.9
MLINKS+=device_get_ivars.9 device_set_ivars.9
MLINKS+=device_get_name.9 device_get_nameunit.9
MLINKS+=device_get_state.9 device_busy.9 \
diff --git a/share/man/man9/device_get_children.9 b/share/man/man9/device_get_children.9
index f9c36971e9b5..45f8f468531b 100644
--- a/share/man/man9/device_get_children.9
+++ b/share/man/man9/device_get_children.9
@@ -1,6 +1,7 @@
.\" -*- nroff -*-
.\"
.\" Copyright (c) 1998 Doug Rabson
+.\" Copyright (c) 2025 Dag-Erling Smørgrav <des@FreeBSD.org>
.\"
.\" All rights reserved.
.\"
@@ -26,21 +27,27 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd August 23, 2008
+.Dd November 28, 2025
.Dt DEVICE_GET_CHILDREN 9
.Os
.Sh NAME
-.Nm device_get_children
-.Nd get a list of devices connected to a device
+.Nm device_get_children ,
+.Nm device_has_children
+.Nd examine devices connected to a device
.Sh SYNOPSIS
.In sys/param.h
.In sys/bus.h
.Ft int
.Fn device_get_children "device_t dev" "device_t **devlistp" "int *devcountp"
+.Ft bool
+.Fn device_has_children "device_t dev"
.Sh DESCRIPTION
-Retrieve a list of all device instances currently connected to
-.Pa dev
-and return the list in
+The
+.Nm device_get_children
+function retrieves a list of all device instances currently connected
+to
+.Fa dev .
+It returns the list in
.Fa *devlistp
and the count in
.Fa *devcountp .
@@ -50,11 +57,35 @@ The memory allocated for the list should be freed using
and
.Fa devcountp
are not changed when an error is returned.
+.Pp
+As a special case, if
+.Fa devlistp
+is null, no memory is allocated but the count is still returned in
+.Fa *devcountp .
+.Pp
+The
+.Nm device_has_children
+function returns
+.Dv true
+if
+.Fa dev
+has at least one child and
+.Dv false
+if it has none.
.Sh RETURN VALUES
-Zero is returned on success, otherwise an appropriate error is returned.
+The
+.Nm device_get_children
+function returns zero on success and an appropriate error otherwise.
+The
+.Nm device_has_children
+function returns true if the specified device has at least one child
+and false otherwise.
.Sh SEE ALSO
.Xr devclass 9 ,
.Xr device 9
.Sh AUTHORS
+.An -nosplit
This manual page was written by
-.An Doug Rabson .
+.An Doug Rabson Aq Mt dfr@FreeBSD.org
+and
+.An Dag-Erling Sm\(/orgrav Aq Mt des@FreeBSD.org .
diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index bf5bda7e058d..f75345415265 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -1858,6 +1858,10 @@ device_get_children(device_t dev, device_t **devlistp, int *devcountp)
TAILQ_FOREACH(child, &dev->children, link) {
count++;
}
+ if (devlistp == NULL) {
+ *devcountp = count;
+ return (0);
+ }
if (count == 0) {
*devlistp = NULL;
*devcountp = 0;
@@ -1880,6 +1884,20 @@ device_get_children(device_t dev, device_t **devlistp, int *devcountp)
return (0);
}
+/**
+ * @brief Check if a device has children
+ *
+ * @param dev the device to examine
+ *
+ * @rerval true the device has at least one child
+ * @retval false the device has no children
+ */
+bool
+device_has_children(device_t dev)
+{
+ return (!TAILQ_EMPTY(&dev->children));
+}
+
/**
* @brief Return the current driver for the device or @c NULL if there
* is no driver currently attached
diff --git a/sys/sys/bus.h b/sys/sys/bus.h
index dda27f4737b2..487d2799221b 100644
--- a/sys/sys/bus.h
+++ b/sys/sys/bus.h
@@ -671,6 +671,7 @@ device_state_t device_get_state(device_t dev);
int device_get_unit(device_t dev);
struct sysctl_ctx_list *device_get_sysctl_ctx(device_t dev);
struct sysctl_oid *device_get_sysctl_tree(device_t dev);
+bool device_has_children(device_t dev);
int device_has_quiet_children(device_t dev);
int device_is_alive(device_t dev); /* did probe succeed? */
int device_is_attached(device_t dev); /* did attach succeed? */