Commit 4f42c1b5 authored by Al Viro's avatar Al Viro
Browse files

libfs.c: new helper - next_positive() 



Return nth positive child after given or NULL if there's
less than n left.  dcache_readdir() and dcache_dir_lseek()
switched to it.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 274f5b04

fs/libfs.c

+47 −30
Original line number Diff line number Diff line
@@ -84,6 +84,39 @@ int dcache_dir_close(struct inode *inode, struct file *file) 
}

EXPORT_SYMBOL(dcache_dir_close);



/* parent is locked at least shared */

static struct dentry *next_positive(struct dentry *parent,

				    struct list_head *from,

				    int count)

{

	struct dentry *res = NULL;

	struct list_head *p;



	spin_lock(&parent->d_lock);

	for (p = from->next; p != &parent->d_subdirs; p = p->next) {

		struct dentry *d = list_entry(p, struct dentry, d_child);

		if (simple_positive(d) && !--count) {

			res = d;

			break;

		}

	}

	spin_unlock(&parent->d_lock);

	return res;

}



static void move_cursor(struct dentry *cursor, struct list_head *after)

{

	struct dentry *parent = cursor->d_parent;



	spin_lock(&parent->d_lock);

	__list_del(cursor->d_child.prev, cursor->d_child.next);

	if (after)

		list_add(&cursor->d_child, after);

	else

		list_add_tail(&cursor->d_child, &parent->d_subdirs);

	spin_unlock(&parent->d_lock);

}



loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)

{

	struct dentry *dentry = file->f_path.dentry;
@@ -99,24 +132,13 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence) 
	if (offset != file->f_pos) {

		file->f_pos = offset;

		if (file->f_pos >= 2) {

			struct list_head *p;

			struct dentry *cursor = file->private_data;

			struct dentry *to;

			loff_t n = file->f_pos - 2;



			inode_lock_shared(dentry->d_inode);

			spin_lock(&dentry->d_lock);

			/* d_lock not required for cursor */

			list_del(&cursor->d_child);

			p = dentry->d_subdirs.next;

			while (n && p != &dentry->d_subdirs) {

				struct dentry *next;

				next = list_entry(p, struct dentry, d_child);

				if (simple_positive(next))

					n--;

				p = p->next;

			}

			list_add_tail(&cursor->d_child, p);

			spin_unlock(&dentry->d_lock);

			to = next_positive(dentry, &dentry->d_subdirs, n);

			move_cursor(cursor, to ? &to->d_child : NULL);

			inode_unlock_shared(dentry->d_inode);

		}

	}
@@ -140,30 +162,25 @@ int dcache_readdir(struct file *file, struct dir_context *ctx) 
{

	struct dentry *dentry = file->f_path.dentry;

	struct dentry *cursor = file->private_data;

	struct list_head *p, *q = &cursor->d_child;

	struct list_head *p = &cursor->d_child;

	struct dentry *next;

	bool moved = false;



	if (!dir_emit_dots(file, ctx))

		return 0;

	spin_lock(&dentry->d_lock);

	if (ctx->pos == 2)

		list_move(q, &dentry->d_subdirs);



	for (p = q->next; p != &dentry->d_subdirs; p = p->next) {

		struct dentry *next = list_entry(p, struct dentry, d_child);

		if (!simple_positive(next))

			continue;



		spin_unlock(&dentry->d_lock);

	if (ctx->pos == 2)

		p = &dentry->d_subdirs;

	while ((next = next_positive(dentry, p, 1)) != NULL) {

		if (!dir_emit(ctx, next->d_name.name, next->d_name.len,

			      d_inode(next)->i_ino, dt_type(d_inode(next))))

			return 0;

		spin_lock(&dentry->d_lock);

		/* next is still alive */

		list_move(q, p);

		p = q;

			break;

		moved = true;

		p = &next->d_child;

		ctx->pos++;

	}

	spin_unlock(&dentry->d_lock);

	if (moved)

		move_cursor(cursor, p);

	return 0;

}

EXPORT_SYMBOL(dcache_readdir);