[PATCH 2/4] fs: add path parser for filesystem mount option.

[Hongbo Li <lihongbo22@huawei.com>]

`fsparam_path` uses `fs_param_is_path` to parse the option, but it
is currently empty. The new mount api has considered this option in
`fsconfig`(that is FSCONFIG_SET_PATH). Here we add general path parser
in filesystem layer. Currently, no filesystem uses this function to
parse parameters, we add `void *ptr` in `fs_parse_result` to point to
the target structure(such as `struct inode *`).

Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
---
 fs/fs_parser.c            | 18 ++++++++++++++++++
 include/linux/fs_parser.h |  1 +
 2 files changed, 19 insertions(+)

diff --git a/fs/fs_parser.c b/fs/fs_parser.c
index 48f60ecfcca0..c41a13e564c4 100644
--- a/fs/fs_parser.c
+++ b/fs/fs_parser.c
@@ -367,6 +367,24 @@ EXPORT_SYMBOL(fs_param_is_blockdev);
 int fs_param_is_path(struct p_log *log, const struct fs_parameter_spec *p,
 		     struct fs_parameter *param, struct fs_parse_result *result)
 {
+	int ret;
+	struct filename *f;
+	struct path path;
+
+	if (param->type != fs_value_is_filename)
+		return fs_param_bad_value(log, param);
+	if (!*param->string && (p->flags & fs_param_can_be_empty))
+		return 0;
+
+	f = param->name;
+	ret = filename_lookup(param->dirfd, f, LOOKUP_FOLLOW, &path, NULL);
+	if (ret < 0) {
+		error_plog(log, "%s: Lookup failure for '%s'", param->key, f->name);
+		return fs_param_bad_value(log, param);
+	}
+	result->ptr = d_backing_inode(path.dentry);
+	path_put(&path);
+
 	return 0;
 }
 EXPORT_SYMBOL(fs_param_is_path);
diff --git a/include/linux/fs_parser.h b/include/linux/fs_parser.h
index d3350979115f..489c71d06a5f 100644
--- a/include/linux/fs_parser.h
+++ b/include/linux/fs_parser.h
@@ -57,6 +57,7 @@ struct fs_parse_result {
 		int		int_32;		/* For spec_s32/spec_enum */
 		unsigned int	uint_32;	/* For spec_u32{,_octal,_hex}/spec_enum */
 		u64		uint_64;	/* For spec_u64 */
+		const void	*ptr;		/* For spec_ptr */
 	};
 };
 
-- 
2.34.1