Re: [PATCH v2 3/9] mm/mshare: make msharefs writable and support directories

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Jun 29, 2022 at 04:53:54PM -0600, Khalid Aziz wrote:

> +static int
> +msharefs_open(struct inode *inode, struct file *file)
> +{
> +	return simple_open(inode, file);
> +}

Again, whatever for?

> +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);
> +}

And it's different from d_alloc_name() how, exactly?

> +		case S_IFLNK:
> +			inode->i_op = &page_symlink_inode_operations;
> +			break;

Really?  You've got symlinks here?

> +		default:
> +			discard_new_inode(inode);
> +			inode = NULL;

That's an odd way to spell BUG()...

> +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;
> +}

BTW, what's the point of having device nodes on that thing?

> +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;
> +}

Looks remarkably similar to something I've seen somewhere... fs/libfs.c,
if I'm not mistaken...

Sarcasm aside, what's wrong with using simple_fill_super()?