Return finer grain errors in libzfs unmount_one

Added errno mappings to unmount_one() in libzfs.  Changed do_unmount() 
implementation to return errno errors directly like is done for 
do_mount() and others.

Reviewed-by: Mark Maybee <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Don Brady <[email protected]>
Closes #11681

Author: Don Brady

lib/libzfs/libzfs_mount.c

@@ -22,7 +22,7 @@
 /*
  * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2014, 2020 by Delphix. All rights reserved.
+ * Copyright (c) 2014, 2021 by Delphix. All rights reserved.
  * Copyright 2016 Igor Kozhukhov <[email protected]>
  * Copyright 2017 RackTop Systems.
  * Copyright (c) 2018 Datto Inc.
@@ -553,7 +553,28 @@ unmount_one(libzfs_handle_t *hdl, const char *mountpoint, int flags)
 
 	error = do_unmount(mountpoint, flags);
 	if (error != 0) {
-		return (zfs_error_fmt(hdl, EZFS_UMOUNTFAILED,
+		int libzfs_err;
+
+		switch (error) {
+		case EBUSY:
+			libzfs_err = EZFS_BUSY;
+			break;
+		case EIO:
+			libzfs_err = EZFS_IO;
+			break;
+		case ENOENT:
+			libzfs_err = EZFS_NOENT;
+			break;
+		case ENOMEM:
+			libzfs_err = EZFS_NOMEM;
+			break;
+		case EPERM:
+			libzfs_err = EZFS_PERM;
+			break;
+		default:
+			libzfs_err = EZFS_UMOUNTFAILED;
+		}
+		return (zfs_error_fmt(hdl, libzfs_err,
 		    dgettext(TEXT_DOMAIN, "cannot unmount '%s'"),
 		    mountpoint));
 	}

lib/libzfs/os/freebsd/libzfs_zmount.c

@@ -128,8 +128,9 @@ do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts, int flags)
 int
 do_unmount(const char *mntpt, int flags)
 {
-
-	return (unmount(mntpt, flags));
+	if (unmount(mntpt, flags) < 0)
+		return (errno);
+	return (0);
 }
 
 int

lib/libzfs/os/linux/libzfs_mount_os.c

@@ -22,7 +22,7 @@
 /*
  * Copyright 2015 Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2014, 2020 by Delphix. All rights reserved.
+ * Copyright (c) 2014, 2021 by Delphix. All rights reserved.
  * Copyright 2016 Igor Kozhukhov <[email protected]>
  * Copyright 2017 RackTop Systems.
  * Copyright (c) 2018 Datto Inc.
@@ -377,7 +377,9 @@ int
 do_unmount(const char *mntpt, int flags)
 {
 	if (!libzfs_envvar_is_set("ZFS_MOUNT_HELPER")) {
-		return (umount2(mntpt, flags));
+		int rv = umount2(mntpt, flags);
+
+		return (rv < 0 ? errno : 0);
 	}
 
 	char force_opt[] = "-f";