linux-kernel - [RFC PATCH v3 03/10] mm/mshare: make msharefs writable and support directories

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Message-ID: <20240903232241.43995-4-anthony.yznaga@oracle.com>
Date: Tue,  3 Sep 2024 16:22:34 -0700
From: Anthony Yznaga <anthony.yznaga@...cle.com>
To: akpm@...ux-foundation.org, willy@...radead.org, markhemm@...glemail.com,
        viro@...iv.linux.org.uk, david@...hat.com, khalid@...nel.org
Cc: anthony.yznaga@...cle.com, andreyknvl@...il.com, dave.hansen@...el.com,
        luto@...nel.org, brauner@...nel.org, arnd@...db.de,
        ebiederm@...ssion.com, catalin.marinas@....com,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mhiramat@...nel.org, rostedt@...dmis.org,
        vasily.averin@...ux.dev, xhao@...ux.alibaba.com, pcc@...gle.com,
        neilb@...e.de, maz@...nel.org
Subject: [RFC PATCH v3 03/10] mm/mshare: make msharefs writable and support directories

From: Khalid Aziz <khalid@...nel.org>

Make msharefs filesystem writable and allow creating directories
to support better access control to mshare'd regions defined in
msharefs.

Signed-off-by: Khalid Aziz <khalid@...nel.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 mm/mshare.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 116 insertions(+), 1 deletion(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index 6562000545e1..f718b8934cdf 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -21,11 +21,126 @@ struct msharefs_info {
 	struct dentry *info_dentry;
 };
 
+static const struct inode_operations msharefs_dir_inode_ops;
+static const struct inode_operations msharefs_file_inode_ops;
+
 static const struct file_operations msharefs_file_operations = {
 	.open		= simple_open,
 	.llseek		= no_llseek,
 };
 
+static struct inode
+*msharefs_get_inode(struct mnt_idmap *idmap, struct super_block *sb,
+			const struct inode *dir, umode_t mode)
+{
+	struct inode *inode = new_inode(sb);
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	inode->i_ino = get_next_ino();
+	inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
+	simple_inode_init_ts(inode);
+
+	switch (mode & S_IFMT) {
+	case S_IFREG:
+		inode->i_op = &msharefs_file_inode_ops;
+		inode->i_fop = &msharefs_file_operations;
+		break;
+	case S_IFDIR:
+		inode->i_op = &msharefs_dir_inode_ops;
+		inode->i_fop = &simple_dir_operations;
+		inc_nlink(inode);
+		break;
+	default:
+		discard_new_inode(inode);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return inode;
+}
+
+static int
+msharefs_mknod(struct mnt_idmap *idmap, struct inode *dir,
+		struct dentry *dentry, umode_t mode)
+{
+	struct inode *inode;
+
+	inode = msharefs_get_inode(idmap, dir->i_sb, dir, mode);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	d_instantiate(dentry, inode);
+	dget(dentry);
+	inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));
+
+	return 0;
+}
+
+static int
+msharefs_create(struct mnt_idmap *idmap, struct inode *dir,
+		struct dentry *dentry, umode_t mode, bool excl)
+{
+	return msharefs_mknod(idmap, dir, dentry, mode | S_IFREG);
+}
+
+static int
+msharefs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
+		struct dentry *dentry, umode_t mode)
+{
+	int ret = msharefs_mknod(idmap, dir, dentry, mode | S_IFDIR);
+
+	if (!ret)
+		inc_nlink(dir);
+	return ret;
+}
+
+static inline bool
+is_msharefs_info_file(const struct dentry *dentry)
+{
+	struct msharefs_info *info = dentry->d_sb->s_fs_info;
+
+	return info->info_dentry == dentry;
+}
+
+static int
+msharefs_rename(struct mnt_idmap *idmap,
+		struct inode *old_dir, struct dentry *old_dentry,
+		struct inode *new_dir, struct dentry *new_dentry,
+		unsigned int flags)
+{
+	if (is_msharefs_info_file(old_dentry) ||
+	    is_msharefs_info_file(new_dentry))
+		return -EPERM;
+
+	return simple_rename(idmap, old_dir, old_dentry, new_dir,
+			     new_dentry, flags);
+}
+
+static int
+msharefs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	if (is_msharefs_info_file(dentry))
+		return -EPERM;
+
+	return simple_unlink(dir, dentry);
+}
+
+static const struct inode_operations msharefs_file_inode_ops = {
+	.setattr	= simple_setattr,
+	.getattr	= simple_getattr,
+};
+
+static const struct inode_operations msharefs_dir_inode_ops = {
+	.create		= msharefs_create,
+	.lookup		= simple_lookup,
+	.link		= simple_link,
+	.unlink		= msharefs_unlink,
+	.mkdir		= msharefs_mkdir,
+	.rmdir		= simple_rmdir,
+	.rename		= msharefs_rename,
+};
+
 static ssize_t
 mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
 		loff_t *ppos)
@@ -104,7 +219,7 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 	inode->i_ino = 1;
 	inode->i_mode = S_IFDIR | 0777;
 	simple_inode_init_ts(inode);
-	inode->i_op = &simple_dir_inode_operations;
+	inode->i_op = &msharefs_dir_inode_ops;
 	inode->i_fop = &simple_dir_operations;
 	set_nlink(inode, 2);
 
-- 
2.43.5