[PATCH v2 19/20] erofs: add 'uuid' mount option

[Jeffle Xu <jefflexu@linux.alibaba.com>]

Introduce 'uuid' mount option to enable the nodev mode, in which erofs
could be mounted from blob files instead of blkdev. By then users could
specify the path of bootstrap blob file containing the complete erofs
image.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/Kconfig |  2 +-
 fs/erofs/super.c | 43 ++++++++++++++++++++++++++++++++++++-------
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index f57255ab88ed..37a2cc82ecc2 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -2,7 +2,7 @@
 
 config EROFS_FS
 	tristate "EROFS filesystem support"
-	depends on BLOCK
+	depends on BLOCK && FSCACHE_ONDEMAND
 	select FS_IOMAP
 	select LIBCRC32C
 	help
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index f058a04a00c7..3f8557bac786 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -400,6 +400,7 @@ enum {
 	Opt_dax,
 	Opt_dax_enum,
 	Opt_device,
+	Opt_uuid,
 	Opt_err
 };
 
@@ -424,6 +425,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
 	fsparam_flag("dax",             Opt_dax),
 	fsparam_enum("dax",		Opt_dax_enum, erofs_dax_param_enums),
 	fsparam_string("device",	Opt_device),
+	fsparam_string("uuid",		Opt_uuid),
 	{}
 };
 
@@ -519,6 +521,12 @@ static int erofs_fc_parse_param(struct fs_context *fc,
 		}
 		++ctx->devs->extra_devices;
 		break;
+	case Opt_uuid:
+		kfree(ctx->opt.uuid);
+		ctx->opt.uuid = kstrdup(param->string, GFP_KERNEL);
+		if (!ctx->opt.uuid)
+			return -ENOMEM;
+		break;
 	default:
 		return -ENOPARAM;
 	}
@@ -593,9 +601,14 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	sb->s_magic = EROFS_SUPER_MAGIC;
 
-	if (!sb_set_blocksize(sb, EROFS_BLKSIZ)) {
-		erofs_err(sb, "failed to set erofs blksize");
-		return -EINVAL;
+	if (erofs_bdev_mode(sb)) {
+		if (!sb_set_blocksize(sb, EROFS_BLKSIZ)) {
+			erofs_err(sb, "failed to set erofs blksize");
+			return -EINVAL;
+		}
+	} else {
+		sb->s_blocksize = EROFS_BLKSIZ;
+		sb->s_blocksize_bits = LOG_BLOCK_SIZE;
 	}
 
 	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
@@ -604,11 +617,12 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	sb->s_fs_info = sbi;
 	sbi->opt = ctx->opt;
-	sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev, &sbi->dax_part_off);
 	sbi->devs = ctx->devs;
 	ctx->devs = NULL;
 
-	if (!erofs_bdev_mode(sb)) {
+	if (erofs_bdev_mode(sb)) {
+		sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev, &sbi->dax_part_off);
+	} else {
 		struct erofs_fscache_context *bootstrap;
 
 		bootstrap = erofs_fscache_get_ctx(sb, ctx->opt.uuid, true);
@@ -616,6 +630,7 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 			return PTR_ERR(bootstrap);
 
 		sbi->bootstrap = bootstrap;
+		sbi->dax_dev = NULL;
 	}
 
 	err = erofs_read_superblock(sb);
@@ -678,6 +693,11 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 
 static int erofs_fc_get_tree(struct fs_context *fc)
 {
+	struct erofs_fs_context *ctx = fc->fs_private;
+
+	if (ctx->opt.uuid)
+		return get_tree_nodev(fc, erofs_fc_fill_super);
+
 	return get_tree_bdev(fc, erofs_fc_fill_super);
 }
 
@@ -727,6 +747,7 @@ static void erofs_fc_free(struct fs_context *fc)
 	struct erofs_fs_context *ctx = fc->fs_private;
 
 	erofs_free_dev_context(ctx->devs);
+	kfree(ctx->opt.uuid);
 	kfree(ctx);
 }
 
@@ -767,7 +788,10 @@ static void erofs_kill_sb(struct super_block *sb)
 
 	WARN_ON(sb->s_magic != EROFS_SUPER_MAGIC);
 
-	kill_block_super(sb);
+	if (erofs_bdev_mode(sb))
+		kill_block_super(sb);
+	else
+		generic_shutdown_super(sb);
 
 	sbi = EROFS_SB(sb);
 	if (!sbi)
@@ -885,7 +909,12 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
 	struct super_block *sb = dentry->d_sb;
 	struct erofs_sb_info *sbi = EROFS_SB(sb);
-	u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
+	u64 id;
+
+	if (erofs_bdev_mode(sb))
+		id = huge_encode_dev(sb->s_bdev->bd_dev);
+	else
+		id = 0; /* TODO */
 
 	buf->f_type = sb->s_magic;
 	buf->f_bsize = EROFS_BLKSIZ;
-- 
2.27.0