Btrfs: make compress and nodatacow mount options mutually exclusive

If a filesystem is mounted with compression and then remounted by adding nodatacow,
the compression is disabled but the compress flag is still visible.
Also, if a filesystem is mounted with nodatacow and then remounted with compression,
nodatacow flag is still present but it's not active.
This patch:
- removes compress flags and notifies that the compression has been disabled if the
  filesystem is mounted with nodatacow
- removes nodatacow and nodatasum flags if mounted with compress.

Signed-off-by: Andrei Popa <andrei.popa@i-neo.ro>

fs/btrfs/super.c

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 0fadcdba..915ac14 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -413,7 +413,15 @@
 			btrfs_set_opt(info->mount_opt, NODATASUM);
 			break;
 		case Opt_nodatacow:
-			printk(KERN_INFO "btrfs: setting nodatacow\n");
+			if (!btrfs_test_opt(root, COMPRESS) ||
+				!btrfs_test_opt(root, FORCE_COMPRESS)) {
+					printk(KERN_INFO "btrfs: setting nodatacow, compression disabled\n");
+			} else {
+				printk(KERN_INFO "btrfs: setting nodatacow\n");
+			}
+			info->compress_type = BTRFS_COMPRESS_NONE;
+			btrfs_clear_opt(info->mount_opt, COMPRESS);
+			btrfs_clear_opt(info->mount_opt, FORCE_COMPRESS);
 			btrfs_set_opt(info->mount_opt, NODATACOW);
 			btrfs_set_opt(info->mount_opt, NODATASUM);
 			break;
@@ -428,10 +436,14 @@
 				compress_type = "zlib";
 				info->compress_type = BTRFS_COMPRESS_ZLIB;
 				btrfs_set_opt(info->mount_opt, COMPRESS);
+				btrfs_clear_opt(info->mount_opt, NODATACOW);
+				btrfs_clear_opt(info->mount_opt, NODATASUM);
 			} else if (strcmp(args[0].from, "lzo") == 0) {
 				compress_type = "lzo";
 				info->compress_type = BTRFS_COMPRESS_LZO;
 				btrfs_set_opt(info->mount_opt, COMPRESS);
+				btrfs_clear_opt(info->mount_opt, NODATACOW);
+				btrfs_clear_opt(info->mount_opt, NODATASUM);
 				btrfs_set_fs_incompat(info, COMPRESS_LZO);
 			} else if (strncmp(args[0].from, "no", 2) == 0) {
 				compress_type = "no";