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From:   Khalid Aziz <khalid.aziz@oracle.com>
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Subject: [PATCH v2 3/9] mm/mshare: make msharefs writable and support directories
Date:   Wed, 29 Jun 2022 16:53:54 -0600
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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.aziz@oracle.com>
---
 mm/mshare.c | 195 +++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 186 insertions(+), 9 deletions(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index 3e448e11c742..2d5924d39221 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -21,11 +21,21 @@
 #include <linux/fileattr.h>
 #include <uapi/linux/magic.h>
 #include <uapi/linux/limits.h>
+#include <uapi/linux/mman.h>
 
 static struct super_block *msharefs_sb;
 
+static const struct inode_operations msharefs_dir_inode_ops;
+static const struct inode_operations msharefs_file_inode_ops;
+
+static int
+msharefs_open(struct inode *inode, struct file *file)
+{
+	return simple_open(inode, file);
+}
+
 static const struct file_operations msharefs_file_operations = {
-	.open		= simple_open,
+	.open		= msharefs_open,
 	.llseek		= no_llseek,
 };
 
@@ -42,6 +52,113 @@ msharefs_d_hash(const struct dentry *dentry, struct qstr *qstr)
 	return 0;
 }
 
+static struct dentry
+*msharefs_alloc_dentry(struct dentry *parent, const char *name)
+{
+	struct dentry *d;
+	struct qstr q;
+	int err;
+
+	q.name = name;
+	q.len = strlen(name);
+
+	err = msharefs_d_hash(parent, &q);
+	if (err)
+		return ERR_PTR(err);
+
+	d = d_alloc(parent, &q);
+	if (d)
+		return d;
+
+	return ERR_PTR(-ENOMEM);
+}
+
+static struct inode
+*msharefs_get_inode(struct super_block *sb, const struct inode *dir,
+			umode_t mode)
+{
+	struct inode *inode = new_inode(sb);
+
+	if (inode) {
+		inode->i_ino = get_next_ino();
+		inode_init_owner(&init_user_ns, inode, dir, mode);
+
+		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(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;
+		case S_IFLNK:
+			inode->i_op = &page_symlink_inode_operations;
+			break;
+		default:
+			discard_new_inode(inode);
+			inode = NULL;
+			break;
+		}
+	}
+
+	return inode;
+}
+
+static int
+msharefs_mknod(struct user_namespace *mnt_userns, struct inode *dir,
+		struct dentry *dentry, umode_t mode, dev_t dev)
+{
+	struct inode *inode;
+	int err = 0;
+
+	inode = msharefs_get_inode(dir->i_sb, dir, mode);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	d_instantiate(dentry, inode);
+	dget(dentry);
+	dir->i_mtime = dir->i_ctime = current_time(dir);
+
+	return err;
+}
+
+static int
+msharefs_create(struct user_namespace *mnt_userns, struct inode *dir,
+		struct dentry *dentry, umode_t mode, bool excl)
+{
+	return msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFREG, 0);
+}
+
+static int
+msharefs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
+		struct dentry *dentry, umode_t mode)
+{
+	int ret = msharefs_mknod(&init_user_ns, dir, dentry, mode | S_IFDIR, 0);
+
+	if (!ret)
+		inc_nlink(dir);
+	return ret;
+}
+
+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		= simple_unlink,
+	.mkdir		= msharefs_mkdir,
+	.rmdir		= simple_rmdir,
+	.mknod		= msharefs_mknod,
+	.rename		= simple_rename,
+};
+
 static void
 mshare_evict_inode(struct inode *inode)
 {
@@ -58,7 +175,7 @@ mshare_info_read(struct file *file, char __user *buf, size_t nbytes,
 {
 	char s[80];
 
-	sprintf(s, "%ld", PGDIR_SIZE);
+	sprintf(s, "%ld\n", PGDIR_SIZE);
 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 }
 
@@ -72,6 +189,38 @@ static const struct super_operations mshare_s_ops = {
 	.evict_inode = mshare_evict_inode,
 };
 
+static int
+prepopulate_files(struct super_block *s, struct inode *dir,
+			struct dentry *root, const struct tree_descr *files)
+{
+	int i;
+	struct inode *inode;
+	struct dentry *dentry;
+
+	for (i = 0; !files->name || files->name[0]; i++, files++) {
+		if (!files->name)
+			continue;
+
+		dentry = msharefs_alloc_dentry(root, files->name);
+		if (!dentry)
+			return -ENOMEM;
+
+		inode = msharefs_get_inode(s, dir, S_IFREG | files->mode);
+		if (!inode) {
+			dput(dentry);
+			return -ENOMEM;
+		}
+		inode->i_mode = S_IFREG | files->mode;
+		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);
+	}
+
+	return 0;
+}
+
 static int
 msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
@@ -79,21 +228,49 @@ msharefs_fill_super(struct super_block *sb, struct fs_context *fc)
 		[2] = { "mshare_info", &mshare_info_ops, 0444},
 		{""},
 	};
-	int err;
+	struct inode *inode;
+	struct dentry *root;
+	int err = 0;
 
-	err = simple_fill_super(sb, MSHARE_MAGIC, mshare_files);
-	if (!err) {
-		msharefs_sb = sb;
-		sb->s_d_op = &msharefs_d_ops;
-		sb->s_op = &mshare_s_ops;
+	sb->s_blocksize		= PAGE_SIZE;
+	sb->s_blocksize_bits	= PAGE_SHIFT;
+	sb->s_magic		= MSHARE_MAGIC;
+	sb->s_op		= &mshare_s_ops;
+	sb->s_d_op		= &msharefs_d_ops;
+	sb->s_time_gran		= 1;
+
+	inode = msharefs_get_inode(sb, NULL, S_IFDIR | 0777);
+	if (!inode) {
+		err = -ENOMEM;
+		goto out;
 	}
+	inode->i_ino = 1;
+	root = d_make_root(inode);
+	if (!root) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	err = prepopulate_files(sb, inode, root, mshare_files);
+	if (err < 0)
+		goto clean_root;
+
+	sb->s_root = root;
+	msharefs_sb = sb;
+	return err;
+
+clean_root:
+	d_genocide(root);
+	shrink_dcache_parent(root);
+	dput(root);
+out:
 	return err;
 }
 
 static int
 msharefs_get_tree(struct fs_context *fc)
 {
-	return get_tree_single(fc, msharefs_fill_super);
+	return get_tree_nodev(fc, msharefs_fill_super);
 }
 
 static const struct fs_context_operations msharefs_context_ops = {
-- 
2.32.0