linux-kernel - [PATCHv4 1/3] libfs: allow simple_fill

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Date:   Fri, 28 Oct 2016 16:52:37 +0100
From:   David Vrabel <david.vrabel@...rix.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>
CC:     David Vrabel <david.vrabel@...rix.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: [PATCHv4 1/3] libfs: allow simple_fill_super() to add symlinks

simple_fill_super() will add symlinks if an entry has mode & S_IFLNK.
The target is provided in the new "link" field.

Signed-off-by: David Vrabel <david.vrabel@...rix.com>
---
v4:
- Use switch for file type.

v2:
- simplified.
---
 fs/libfs.c         | 27 ++++++++++++++++++++++++---
 include/linux/fs.h |  2 +-
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 48826d4..8eabcb1 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -509,6 +509,7 @@ int simple_fill_super(struct super_block *s, unsigned long magic,
 	struct dentry *root;
 	struct dentry *dentry;
 	int i;
+	int ret = -ENOMEM;
 
 	s->s_blocksize = PAGE_SIZE;
 	s->s_blocksize_bits = PAGE_SHIFT;
@@ -550,9 +551,29 @@ int simple_fill_super(struct super_block *s, unsigned long magic,
 			dput(dentry);
 			goto out;
 		}
-		inode->i_mode = S_IFREG | files->mode;
+		switch (files->mode & S_IFMT) {
+		case S_IFLNK:
+			inode->i_mode = files->mode;
+			inode->i_op = &simple_symlink_inode_operations;
+			inode->i_link = kstrdup(files->link, GFP_KERNEL);
+			if (!inode->i_link) {
+				iput(inode);
+				dput(dentry);
+				goto out;
+			}
+			break;
+		case S_IFREG:
+		case 0:
+			inode->i_mode = S_IFREG | files->mode;
+			inode->i_fop = files->ops;
+			break;
+		default:
+			iput(inode);
+			dput(dentry);
+			ret = -EINVAL;
+			goto out;
+		}
 		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
-		inode->i_fop = files->ops;
 		inode->i_ino = i;
 		d_add(dentry, inode);
 	}
@@ -562,7 +583,7 @@ int simple_fill_super(struct super_block *s, unsigned long magic,
 	d_genocide(root);
 	shrink_dcache_parent(root);
 	dput(root);
-	return -ENOMEM;
+	return ret;
 }
 EXPORT_SYMBOL(simple_fill_super);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 16d2b6e..4b64fbb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2988,7 +2988,7 @@ extern const struct file_operations simple_dir_operations;
 extern const struct inode_operations simple_dir_inode_operations;
 extern void make_empty_dir_inode(struct inode *inode);
 extern bool is_empty_dir_inode(struct inode *inode);
-struct tree_descr { char *name; const struct file_operations *ops; int mode; };
+struct tree_descr { char *name; const struct file_operations *ops; int mode; char *link; };
 struct dentry *d_alloc_name(struct dentry *, const char *);
 extern int simple_fill_super(struct super_block *, unsigned long, struct tree_descr *);
 extern int simple_pin_fs(struct file_system_type *, struct vfsmount **mount, int *count);
-- 
2.1.4