Re-share zfsdev_getminor and zfs_onexit_fd_hold

By adding a zfs_file_private accessor to the common
interfaces and some extensions to FreeBSD platform
code it is now possible to share the implementations
for the aforementioned functions.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #10073

module/zfs/zfs_ioctl.c

@@ -7154,6 +7154,41 @@ pool_status_check(const char *name, zfs_ioc_namecheck_t type,
 	return (error);
 }
 
+int
+zfsdev_getminor(int fd, minor_t *minorp)
+{
+	zfsdev_state_t *zs, *fpd;
+	zfs_file_t *fp;
+	int rc;
+
+	ASSERT(!MUTEX_HELD(&zfsdev_state_lock));
+
+	if ((rc = zfs_file_get(fd, &fp)))
+		return (rc);
+
+	fpd = zfs_file_private(fp);
+	if (fpd == NULL)
+		return (SET_ERROR(EBADF));
+
+	mutex_enter(&zfsdev_state_lock);
+
+	for (zs = zfsdev_state_list; zs != NULL; zs = zs->zs_next) {
+
+		if (zs->zs_minor == -1)
+			continue;
+
+		if (fpd == zs) {
+			*minorp = fpd->zs_minor;
+			mutex_exit(&zfsdev_state_lock);
+			return (0);
+		}
+	}
+
+	mutex_exit(&zfsdev_state_lock);
+
+	return (SET_ERROR(EBADF));
+}
+
 static void *
 zfsdev_get_state_impl(minor_t minor, enum zfsdev_state_type which)
 {

module/zfs/zfs_onexit.c

@@ -101,6 +101,38 @@ zfs_onexit_destroy(zfs_onexit_t *zo)
 	kmem_free(zo, sizeof (zfs_onexit_t));
 }
 
+/*
+ * Consumers might need to operate by minor number instead of fd, since
+ * they might be running in another thread (e.g. txg_sync_thread). Callers
+ * of this function must call zfs_onexit_fd_rele() when they're finished
+ * using the minor number.
+ */
+int
+zfs_onexit_fd_hold(int fd, minor_t *minorp)
+{
+	zfs_onexit_t *zo = NULL;
+	int error;
+
+	error = zfsdev_getminor(fd, minorp);
+	if (error) {
+		zfs_onexit_fd_rele(fd);
+		return (error);
+	}
+
+	zo = zfsdev_get_state(*minorp, ZST_ONEXIT);
+	if (zo == NULL) {
+		zfs_onexit_fd_rele(fd);
+		return (SET_ERROR(EBADF));
+	}
+	return (0);
+}
+
+void
+zfs_onexit_fd_rele(int fd)
+{
+	zfs_file_put(fd);
+}
+
 static int
 zfs_onexit_minor_to_state(minor_t minor, zfs_onexit_t **zo)
 {