[RFC PATCH 1/5] erofs: add 'domain_id' mount option for on-demand read sementics

[Jia Zhu]

Introduce 'domain_id' mount option to enable shared domain sementics.
In which case, the related cookie is shared if two mountpoints in the
same domain have the same data blob. Users could specify the name of
domain by this mount option.

Signed-off-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
---
 fs/erofs/internal.h |  1 +
 fs/erofs/super.c    | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index cfee49d33b95..fe435d077f1a 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -76,6 +76,7 @@ struct erofs_mount_opts {
 #endif
 	unsigned int mount_opt;
 	char *fsid;
+	char *domain_id;
 };
 
 struct erofs_dev_context {
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 3173debeaa5a..fb5a84a07bd5 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -440,6 +440,7 @@ enum {
 	Opt_dax_enum,
 	Opt_device,
 	Opt_fsid,
+	Opt_domain_id,
 	Opt_err
 };
 
@@ -465,6 +466,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
 	fsparam_enum("dax",		Opt_dax_enum, erofs_dax_param_enums),
 	fsparam_string("device",	Opt_device),
 	fsparam_string("fsid",		Opt_fsid),
+	fsparam_string("domain_id",	Opt_domain_id),
 	{}
 };
 
@@ -568,6 +570,16 @@ static int erofs_fc_parse_param(struct fs_context *fc,
 			return -ENOMEM;
 #else
 		errorfc(fc, "fsid option not supported");
+#endif
+		break;
+	case Opt_domain_id:
+		kfree(ctx->opt.domain_id);
+		ctx->opt.domain_id = kstrdup(param->string, GFP_KERNEL);
+		if (!ctx->opt.domain_id)
+			return -ENOMEM;
+#ifdef CONFIG_EROFS_FS_ONDEMAND
+#else
+		errorfc(fc, "domain_id option not supported");
 #endif
 		break;
 	default:
@@ -695,6 +707,7 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_fs_info = sbi;
 	sbi->opt = ctx->opt;
 	ctx->opt.fsid = NULL;
+	ctx->opt.domain_id = NULL;
 	sbi->devs = ctx->devs;
 	ctx->devs = NULL;
 
@@ -838,6 +851,7 @@ static void erofs_fc_free(struct fs_context *fc)
 
 	erofs_free_dev_context(ctx->devs);
 	kfree(ctx->opt.fsid);
+	kfree(ctx->opt.domain_id);
 	kfree(ctx);
 }
 
@@ -892,6 +906,7 @@ static void erofs_kill_sb(struct super_block *sb)
 	erofs_fscache_unregister_cookie(&sbi->s_fscache);
 	erofs_fscache_unregister_fs(sb);
 	kfree(sbi->opt.fsid);
+	kfree(sbi->opt.domain_id);
 	kfree(sbi);
 	sb->s_fs_info = NULL;
 }
@@ -1044,6 +1059,8 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
 #ifdef CONFIG_EROFS_FS_ONDEMAND
 	if (opt->fsid)
 		seq_printf(seq, ",fsid=%s", opt->fsid);
+	if (opt->domain_id)
+		seq_printf(seq, ",domain_id=%s", opt->domain_id);
 #endif
 	return 0;
 }
-- 
2.20.1