[PATCH v3 9/9] erofs: introduce 'sharecache' mount option

[Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>]

Introduce 'sharecache' mount option to enable page cache sharing in
fscache mode.

Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
---
 Documentation/filesystems/erofs.rst |  2 ++
 fs/erofs/inode.c                    |  4 ++++
 fs/erofs/internal.h                 |  3 +++
 fs/erofs/super.c                    | 13 +++++++++++++
 4 files changed, 22 insertions(+)

diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
index a43aacf1494e..1478c4d168e2 100644
--- a/Documentation/filesystems/erofs.rst
+++ b/Documentation/filesystems/erofs.rst
@@ -122,6 +122,8 @@ device=%s              Specify a path to an extra device to be used together.
 fsid=%s                Specify a filesystem image ID for Fscache back-end.
 domain_id=%s           Specify a domain ID in fscache mode so that different images
                        with the same blobs under a given domain ID can share storage.
+(no)sharecache         Enable page cache sharing among different images in the
+                       same domain.
 ===================    =========================================================
 
 Sysfs Entries
diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index d3b8736fa124..31d3ab8443d1 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -262,6 +262,10 @@ static int erofs_fill_inode(struct inode *inode)
 		inode->i_op = &erofs_generic_iops;
 		if (erofs_inode_is_data_compressed(vi->datalayout))
 			inode->i_fop = &generic_ro_fops;
+#ifdef CONFIG_EROFS_FS_ONDEMAND
+		else if (erofs_can_share_page(inode))
+			inode->i_fop = &erofs_fscache_share_file_fops;
+#endif
 		else
 			inode->i_fop = &erofs_file_fops;
 		break;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 6019b076c625..c3ac6d613eb1 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -374,6 +374,9 @@ static inline bool erofs_can_share_page(struct inode *inode)
 	struct erofs_inode *vi = EROFS_I(inode);
 	struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
 
+	if (!test_opt(&sbi->opt, SHARE_CACHE))
+		return false;
+
 	/* enable page cache sharing only in share domain mode */
 	if (!erofs_is_fscache_mode(inode->i_sb) || !sbi->domain_id)
 		return false;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 835b69c9511b..d05346d34ed8 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -456,6 +456,7 @@ enum {
 	Opt_device,
 	Opt_fsid,
 	Opt_domain_id,
+	Opt_sharecache,
 	Opt_err
 };
 
@@ -482,6 +483,7 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
 	fsparam_string("device",	Opt_device),
 	fsparam_string("fsid",		Opt_fsid),
 	fsparam_string("domain_id",	Opt_domain_id),
+	fsparam_flag_no("sharecache",	Opt_sharecache),
 	{}
 };
 
@@ -590,9 +592,16 @@ static int erofs_fc_parse_param(struct fs_context *fc,
 		if (!ctx->domain_id)
 			return -ENOMEM;
 		break;
+	case Opt_sharecache:
+		if (result.boolean)
+			set_opt(&ctx->opt, SHARE_CACHE);
+		else
+			clear_opt(&ctx->opt, SHARE_CACHE);
+		break;
 #else
 	case Opt_fsid:
 	case Opt_domain_id:
+	case Opt_sharecache:
 		errorfc(fc, "%s option not supported", erofs_fs_parameters[opt].name);
 		break;
 #endif
@@ -1108,6 +1117,10 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_printf(seq, ",fsid=%s", sbi->fsid);
 	if (sbi->domain_id)
 		seq_printf(seq, ",domain_id=%s", sbi->domain_id);
+	if (test_opt(opt, SHARE_CACHE))
+		seq_puts(seq, ",sharecache");
+	else
+		seq_puts(seq, ",nosharecache");
 #endif
 	return 0;
 }
-- 
2.19.1.6.gb485710b