zfs_file: rename zfs_file_fallocate to zfs_file_deallocate

We only use it on a specific way: to punch a hole in (make sparse) a
region of a file, in order to implement TRIM-like behaviour.

So, call the op "deallocate", and move the Linux-style mode flags down
into the Linux implementation, since they're an implementation detail.

FreeBSD gets a no-op stub (for the moment).

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #16496

module/os/freebsd/zfs/vdev_file.c

@@ -260,16 +260,9 @@ vdev_file_io_start(zio_t *zio)
 		zio_execute(zio);
 		return;
 	} else if (zio->io_type == ZIO_TYPE_TRIM) {
-#ifdef notyet
-		int mode = 0;
-
 		ASSERT3U(zio->io_size, !=, 0);
-
-		/* XXX FreeBSD has no fallocate routine in file ops */
-		zio->io_error = zfs_file_fallocate(vf->vf_file,
-		    mode, zio->io_offset, zio->io_size);
-#endif
-		zio->io_error = SET_ERROR(ENOTSUP);
+		zio->io_error = zfs_file_deallocate(vf->vf_file,
+		    zio->io_offset, zio->io_size);
 		zio_execute(zio);
 		return;
 	}

module/os/freebsd/zfs/zfs_file_os.c

@@ -285,6 +285,20 @@ zfs_file_fsync(zfs_file_t *fp, int flags)
 	return (zfs_vop_fsync(fp->f_vnode));
 }
 
+/*
+ * deallocate - zero and/or deallocate file storage
+ *
+ * fp - file pointer
+ * offset - offset to start zeroing or deallocating
+ * len - length to zero or deallocate
+ */
+int
+zfs_file_deallocate(zfs_file_t *fp, loff_t offset, loff_t len)
+{
+	(void) fp, (void) offset, (void) len;
+	return (SET_ERROR(EOPNOTSUPP));
+}
+
 zfs_file_t *
 zfs_file_get(int fd)
 {