Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Fri, 23 Feb 2024 11:41:55 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the famfs fs_context_operations and
> famfs_get_inode() which is used by the context operations.
> 
> Signed-off-by: John Groves <john@groves.net>
Trivial comments inline.

> ---
>  fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 178 insertions(+)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 82c861998093..f98f82962d7b 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -41,6 +41,50 @@ static const struct super_operations famfs_ops;
>  static const struct inode_operations famfs_file_inode_operations;
>  static const struct inode_operations famfs_dir_inode_operations;
>  
> +static struct inode *famfs_get_inode(
> +	struct super_block *sb,
> +	const struct inode *dir,
> +	umode_t             mode,
> +	dev_t               dev)
> +{
> +	struct inode *inode = new_inode(sb);
> +
> +	if (inode) {
reverse logic would be simpler and reduce indent.

	if (!inode)
		return NULL;


> +		struct timespec64       tv;
> +
> +		inode->i_ino = get_next_ino();
> +		inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
> +		inode->i_mapping->a_ops = &ram_aops;
> +		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> +		mapping_set_unevictable(inode->i_mapping);
> +		tv = inode_set_ctime_current(inode);
> +		inode_set_mtime_to_ts(inode, tv);
> +		inode_set_atime_to_ts(inode, tv);
> +
> +		switch (mode & S_IFMT) {
> +		default:
> +			init_special_inode(inode, mode, dev);
> +			break;
> +		case S_IFREG:
> +			inode->i_op = &famfs_file_inode_operations;
> +			inode->i_fop = &famfs_file_operations;
> +			break;
> +		case S_IFDIR:
> +			inode->i_op = &famfs_dir_inode_operations;
> +			inode->i_fop = &simple_dir_operations;
> +
> +			/* Directory inodes start off with i_nlink == 2 (for "." entry) */
> +			inc_nlink(inode);
> +			break;
> +		case S_IFLNK:
> +			inode->i_op = &page_symlink_inode_operations;
> +			inode_nohighmem(inode);
> +			break;
> +		}
> +	}
> +	return inode;
> +}
> +
>  /**********************************************************************************
>   * famfs super_operations
>   *
> @@ -150,6 +194,140 @@ famfs_open_device(
>  	return 0;
>  }
>  
> +/*****************************************************************************************
> + * fs_context_operations
> + */
> +static int
> +famfs_fill_super(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	struct famfs_fs_info *fsi = sb->s_fs_info;
> +	struct inode *inode;
> +	int rc = 0;
Always initialized so no need to do it here.

> +
> +	sb->s_maxbytes		= MAX_LFS_FILESIZE;
> +	sb->s_blocksize		= PAGE_SIZE;
> +	sb->s_blocksize_bits	= PAGE_SHIFT;
> +	sb->s_magic		= FAMFS_MAGIC;
> +	sb->s_op		= &famfs_ops;
> +	sb->s_time_gran		= 1;
> +
> +	rc = famfs_open_device(sb, fc);
> +	if (rc)
> +		goto out;
		return rc; //unless you need to do more in out in later patch..

> +
> +	inode = famfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
> +	sb->s_root = d_make_root(inode);
> +	if (!sb->s_root)
> +		rc = -ENOMEM;
		return -ENOMEM;

	return 0;

> +
> +out:
> +	return rc;
> +}
> +
> +enum famfs_param {
> +	Opt_mode,
> +	Opt_dax,
Why capital O?

> +};
> +

...

> +
> +static DEFINE_MUTEX(famfs_context_mutex);
> +static LIST_HEAD(famfs_context_list);
> +
> +static int famfs_get_tree(struct fs_context *fc)
> +{
> +	struct famfs_fs_info *fsi_entry;
> +	struct famfs_fs_info *fsi = fc->s_fs_info;
> +
> +	fsi->rootdev = kstrdup(fc->source, GFP_KERNEL);
> +	if (!fsi->rootdev)
> +		return -ENOMEM;
> +
> +	/* Fail if famfs is already mounted from the same device */
> +	mutex_lock(&famfs_context_mutex);

New toys might be good to use from start to avoid need for explicit
unlocks in error paths.

	scoped_guard(mutex, &famfs_context_mutex) {
		list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
			if (strcmp(fsi_entry->rootdev, cs_source) == 0) {
			//could invert with a continue to reduce indent
			// or factor this out as a little helper.
			// famfs_check_not_mounted()
				pr_err();
				return -EALREADY;
			}
		}	
		list_add(&fsi->fs_list, &famfs_context_list);
	}

	return get_tree_nodev(...

> +	list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
> +		if (strcmp(fsi_entry->rootdev, fc->source) == 0) {
> +			mutex_unlock(&famfs_context_mutex);
> +			pr_err("%s: already mounted from rootdev %s\n", __func__, fc->source);
> +			return -EALREADY;
> +		}
> +	}
> +
> +	list_add(&fsi->fsi_list, &famfs_context_list);
> +	mutex_unlock(&famfs_context_mutex);
> +
> +	return get_tree_nodev(fc, famfs_fill_super);
> +
> +}

>  
>  MODULE_LICENSE("GPL");