btrfs: move space cache settings into open_ctree

Currently we pre-load the space cache settings in btrfs_parse_options,
however when we switch to the new mount API the mount option parsing
will happen before we have the super block loaded.  Add a helper to set
the appropriate options based on the fs settings, this will allow us to
have consistent free space cache settings.

This also folds in the space cache related decisions we make for subpage
sectorsize support, so all of this is done in one place.

Since this was being called by parse options it looks like we're
changing the behavior of remount, but in fact we aren't.  The
pre-loading of the free space cache settings is done because we want to
handle the case of users not using any space_cache options, we'll derive
the appropriate mount option based on the on disk state.  On remount
this wouldn't reset anything as we'll have cleared the v1 cache
generation if we mounted -o nospace_cache.  Similarly it's impossible to
turn off the free space tree without specifically saying -o
nospace_cache,clear_cache, which will delete the free space tree and
clear the compat_ro option.  Again in this case calling this code in
remount wouldn't result in any change.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -3305,6 +3305,12 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	fs_info->csums_per_leaf = BTRFS_MAX_ITEM_SIZE(fs_info) / fs_info->csum_size;
 	fs_info->stripesize = stripesize;
 
+	/*
+	 * Handle the space caching options appropriately now that we have the
+	 * super block loaded and validated.
+	 */
+	btrfs_set_free_space_cache_settings(fs_info);
+
 	ret = btrfs_parse_options(fs_info, options, sb->s_flags);
 	if (ret)
 		goto fail_alloc;
@@ -3316,17 +3322,6 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	if (sectorsize < PAGE_SIZE) {
 		struct btrfs_subpage_info *subpage_info;
 
-		/*
-		 * V1 space cache has some hardcoded PAGE_SIZE usage, and is
-		 * going to be deprecated.
-		 *
-		 * Force to use v2 cache for subpage case.
-		 */
-		btrfs_clear_opt(fs_info->mount_opt, SPACE_CACHE);
-		btrfs_set_and_info(fs_info, FREE_SPACE_TREE,
-			"forcing free space tree for sector size %u with page size %lu",
-			sectorsize, PAGE_SIZE);
-
 		btrfs_warn(fs_info,
 		"read-write for sector size %u with page size %lu is experimental",
 			   sectorsize, PAGE_SIZE);

fs/btrfs/super.c

@@ -271,6 +271,43 @@ static bool check_options(struct btrfs_fs_info *info, unsigned long flags)
 	return ret;
 }
 
+/*
+ * This is subtle, we only call this during open_ctree().  We need to pre-load
+ * the mount options with the on-disk settings.  Before the new mount API took
+ * effect we would do this on mount and remount.  With the new mount API we'll
+ * only do this on the initial mount.
+ *
+ * This isn't a change in behavior, because we're using the current state of the
+ * file system to set the current mount options.  If you mounted with special
+ * options to disable these features and then remounted we wouldn't revert the
+ * settings, because mounting without these features cleared the on-disk
+ * settings, so this being called on re-mount is not needed.
+ */
+void btrfs_set_free_space_cache_settings(struct btrfs_fs_info *fs_info)
+{
+	if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
+		btrfs_set_opt(fs_info->mount_opt, FREE_SPACE_TREE);
+	else if (btrfs_free_space_cache_v1_active(fs_info)) {
+		if (btrfs_is_zoned(fs_info)) {
+			btrfs_info(fs_info,
+			"zoned: clearing existing space cache");
+			btrfs_set_super_cache_generation(fs_info->super_copy, 0);
+		} else {
+			btrfs_set_opt(fs_info->mount_opt, SPACE_CACHE);
+		}
+	}
+
+	if (fs_info->sectorsize < PAGE_SIZE) {
+		btrfs_clear_opt(fs_info->mount_opt, SPACE_CACHE);
+		if (!btrfs_test_opt(fs_info, FREE_SPACE_TREE)) {
+			btrfs_info(fs_info,
+				   "forcing free space tree for sector size %u with page size %lu",
+				   fs_info->sectorsize, PAGE_SIZE);
+			btrfs_set_opt(fs_info->mount_opt, FREE_SPACE_TREE);
+		}
+	}
+}
+
 static int parse_rescue_options(struct btrfs_fs_info *info, const char *options)
 {
 	char *opts;
@@ -350,18 +387,6 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 	bool saved_compress_force;
 	int no_compress = 0;
 
-	if (btrfs_fs_compat_ro(info, FREE_SPACE_TREE))
-		btrfs_set_opt(info->mount_opt, FREE_SPACE_TREE);
-	else if (btrfs_free_space_cache_v1_active(info)) {
-		if (btrfs_is_zoned(info)) {
-			btrfs_info(info,
-			"zoned: clearing existing space cache");
-			btrfs_set_super_cache_generation(info->super_copy, 0);
-		} else {
-			btrfs_set_opt(info->mount_opt, SPACE_CACHE);
-		}
-	}
-
 	/*
 	 * Even the options are empty, we still need to do extra check
 	 * against new flags
@@ -654,8 +679,13 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 			 * compat_ro(FREE_SPACE_TREE) set, and we aren't going
 			 * to allow v1 to be set for extent tree v2, simply
 			 * ignore this setting if we're extent tree v2.
+			 *
+			 * For subpage blocksize we don't allow space cache v1,
+			 * and we'll turn on v2, so we can skip the settings
+			 * here as well.
 			 */
-			if (btrfs_fs_incompat(info, EXTENT_TREE_V2))
+			if (btrfs_fs_incompat(info, EXTENT_TREE_V2) ||
+			    info->sectorsize < PAGE_SIZE)
 				break;
 			if (token == Opt_space_cache ||
 			    strcmp(args[0].from, "v1") == 0) {

fs/btrfs/super.h

@@ -8,6 +8,7 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 int btrfs_sync_fs(struct super_block *sb, int wait);
 char *btrfs_get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
 					  u64 subvol_objectid);
+void btrfs_set_free_space_cache_settings(struct btrfs_fs_info *fs_info);
 
 static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)
 {