From b727163db93c68ebce3ca970c4245d959795d5b9 Mon Sep 17 00:00:00 2001
From: rmacklem <64620010+rmacklem@users.noreply.github.com>
Date: Tue, 9 Sep 2025 08:52:40 -0700
Subject: [PATCH] zfs_vnops_os.c: Add support for the _PC_CLONE_BLKSIZE name

FreeBSD now has a pathconf name called _PC_CLONE_BLKSIZE
which is the block size supported for block cloning for
the file system.  Since ZFS's block size varies per file,
return the largest size likely to be used, or zero if block
cloning is not supported.

Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Rick Macklem <rmacklem@uoguelph.ca>
Closes #17645
---
 module/os/freebsd/zfs/zfs_vnops_os.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/module/os/freebsd/zfs/zfs_vnops_os.c b/module/os/freebsd/zfs/zfs_vnops_os.c
index 515ee50df..e150874c6 100644
--- a/module/os/freebsd/zfs/zfs_vnops_os.c
+++ b/module/os/freebsd/zfs/zfs_vnops_os.c
@@ -61,6 +61,7 @@
 #include <sys/fs/zfs.h>
 #include <sys/dmu.h>
 #include <sys/dmu_objset.h>
+#include <sys/dsl_dataset.h>
 #include <sys/spa.h>
 #include <sys/txg.h>
 #include <sys/dbuf.h>
@@ -5729,6 +5730,9 @@ zfs_freebsd_pathconf(struct vop_pathconf_args *ap)
 {
 	ulong_t val;
 	int error;
+#ifdef _PC_CLONE_BLKSIZE
+	zfsvfs_t *zfsvfs;
+#endif
 
 	error = zfs_pathconf(ap->a_vp, ap->a_name, &val,
 	    curthread->td_ucred, NULL);
@@ -5774,6 +5778,21 @@ zfs_freebsd_pathconf(struct vop_pathconf_args *ap)
 	case _PC_HAS_HIDDENSYSTEM:
 		*ap->a_retval = 1;
 		return (0);
+#endif
+#ifdef _PC_CLONE_BLKSIZE
+	case _PC_CLONE_BLKSIZE:
+		zfsvfs = (zfsvfs_t *)ap->a_vp->v_mount->mnt_data;
+		if (zfs_bclone_enabled &&
+		    spa_feature_is_enabled(dmu_objset_spa(zfsvfs->z_os),
+		    SPA_FEATURE_BLOCK_CLONING))
+			*ap->a_retval = dsl_dataset_feature_is_active(
+			    zfsvfs->z_os->os_dsl_dataset,
+			    SPA_FEATURE_LARGE_BLOCKS) ?
+			    SPA_MAXBLOCKSIZE :
+			    SPA_OLD_MAXBLOCKSIZE;
+		else
+			*ap->a_retval = 0;
+		return (0);
 #endif
 	default:
 		return (vop_stdpathconf(ap));