On Fri, Dec 25, 2020 at 04:51:13PM +0300, Konstantin Komarov wrote:
> +static int ntfs_readdir(struct file *file, struct dir_context *ctx)
> +{
> + const struct INDEX_ROOT *root;
> + u64 vbo;
> + size_t bit;
> + loff_t eod;
> + int err = 0;
> + struct inode *dir = file_inode(file);
> + struct ntfs_inode *ni = ntfs_i(dir);
> + struct super_block *sb = dir->i_sb;
> + struct ntfs_sb_info *sbi = sb->s_fs_info;
> + loff_t i_size = dir->i_size;
I appreciate directories are never likely to exceed 4GB, but why not
use i_size_read() here?
> + u32 pos = ctx->pos;
> + u8 *name = NULL;
> + struct indx_node *node = NULL;
> + u8 index_bits = ni->dir.index_bits;
> +
> + /* name is a buffer of PATH_MAX length */
> + static_assert(NTFS_NAME_LEN * 4 < PATH_MAX);
> +
> + if (ni->dir.changed) {
> + ni->dir.changed = false;
> + pos = 0;
> + }
I don't think that 'changed' as implemented is all that useful. If you
have one reader and one-or-more writers, the reader will go back to the
start, but if you have two readers and one-or-more writers, only one
reader will see the 'changed' flag before the other one resets it.
You need to use a sequence counter or something if you want this to be
proof against multiple readers, and honestly I don't think it's worth it.
POSIX says:
: If a file is removed from or added to the directory after the most
: recent call to opendir() or rewinddir(), whether a subsequent call to
: readdir() returns an entry for that file is unspecified.
> + eod = i_size + sbi->record_size;
> +
> + if (pos >= eod)
> + return 0;
> +
> + if (!dir_emit_dots(file, ctx))
> + return 0;
> +
> + /* allocate PATH_MAX bytes */
> + name = __getname();
> + if (!name)
> + return -ENOMEM;
> +
> + ni_lock(ni);
What is ni_lock() protecting against here? You're being called under the
protection of dir->i_rwsem, which excludes simultaneous calls to create,
link, mknod, symlink, mkdir, unlink, rmdir and rename.
> +const struct file_operations ntfs_dir_operations = {
> + .llseek = generic_file_llseek,
> + .read = generic_read_dir,
> + .iterate = ntfs_readdir,
This should probably be iterate_shared so multiple calls to readdir can
be in progress at once (see Documentation/filesystems/porting)
