FreeBSD: Correct _PC_MIN_HOLE_SIZE

The actual minimum hole size on ZFS is variable, but we always report
SPA_MINBLOCKSIZE, which is 512.  This may lead applications to believe
that they can reliably create holes at 512-byte boundaries and waste
resources trying to punch holes that ZFS ends up filling anyway.

* In the general case, if the vnode is a regular file, return its
  current block size, or the record size if the file is smaller than
  its own block size.  If the vnode is a directory, return the dataset
  record size.  If it is neither a regular file nor a directory,
  return EINVAL.

* In the control directory case, always return EINVAL.

Signed-off-by: Dag-Erling Smørgrav <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Closes openzfs#17750

Author: dag-erling

module/os/freebsd/zfs/zfs_ctldir.c

@@ -764,8 +764,7 @@ zfsctl_common_pathconf(struct vop_pathconf_args *ap)
 		return (0);
 
 	case _PC_MIN_HOLE_SIZE:
-		*ap->a_retval = (int)SPA_MINBLOCKSIZE;
-		return (0);
+		return (EINVAL);
 
 	case _PC_ACL_EXTENDED:
 		*ap->a_retval = 0;

module/os/freebsd/zfs/zfs_vnops_os.c

@@ -4118,6 +4118,7 @@ zfs_pathconf(vnode_t *vp, int cmd, ulong_t *valp, cred_t *cr,
 {
 	znode_t *zp;
 	zfsvfs_t *zfsvfs;
+	uint_t blksize, iosize;
 	int error;
 
 	switch (cmd) {
@@ -4129,8 +4130,20 @@ zfs_pathconf(vnode_t *vp, int cmd, ulong_t *valp, cred_t *cr,
 		*valp = 64;
 		return (0);
 	case _PC_MIN_HOLE_SIZE:
-		*valp = (int)SPA_MINBLOCKSIZE;
-		return (0);
+		iosize = vp->v_mount->mnt_stat.f_iosize;
+		if (vp->v_type == VREG) {
+			zp = VTOZ(vp);
+			blksize = zp->z_blksz;
+			if (zp->z_size <= blksize)
+				blksize = MAX(blksize, iosize);
+			*valp = (int)blksize;
+			return (0);
+		}
+		if (vp->v_type == VDIR) {
+			*valp = (int)iosize;
+			return (0);
+		}
+		return (EINVAL);
 	case _PC_ACL_EXTENDED:
 #if 0		/* POSIX ACLs are not implemented for ZFS on FreeBSD yet. */
 		zp = VTOZ(vp);