erofs: register fscache volume

A new fscache based mode is going to be introduced for erofs, in which
case on-demand read semantics is implemented through fscache.

As the first step, register fscache volume for each erofs filesystem.
That means, data blobs can not be shared among erofs filesystems. In the
following iteration, we are going to introduce the domain semantics, in
which case several erofs filesystems can belong to one domain, and data
blobs can be shared among these erofs filesystems of one domain.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220425122143.56815-12-jefflexu@linux.alibaba.com
Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
new file mode 100644
index 000000000000..7a6d0239ebb1
--- /dev/null
+++ b/fs/erofs/fscache.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2022, Alibaba Cloud
+ */
+#include <linux/fscache.h>
+#include "internal.h"
+
+int erofs_fscache_register_fs(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	struct fscache_volume *volume;
+	char *name;
+	int ret = 0;
+
+	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
+	if (!name)
+		return -ENOMEM;
+
+	volume = fscache_acquire_volume(name, NULL, NULL, 0);
+	if (IS_ERR_OR_NULL(volume)) {
+		erofs_err(sb, "failed to register volume for %s", name);
+		ret = volume ? PTR_ERR(volume) : -EOPNOTSUPP;
+		volume = NULL;
+	}
+
+	sbi->volume = volume;
+	kfree(name);
+	return ret;
+}
+
+void erofs_fscache_unregister_fs(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	fscache_relinquish_volume(sbi->volume, NULL, false);
+	sbi->volume = NULL;
+}