[PATCH 1/2] devfs: Add symlink support

[Sascha Hauer]

Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
 fs/devfs-core.c  | 72 ++++++++++++++++++++++++++++++++++++++++++++++----------
 fs/devfs.c       | 27 ++++++++++++++++++++-
 include/driver.h |  4 ++++
 3 files changed, 89 insertions(+), 14 deletions(-)

diff --git a/fs/devfs-core.c b/fs/devfs-core.c
index 2541ea3..1e899a1 100644
--- a/fs/devfs-core.c
+++ b/fs/devfs-core.c
@@ -46,7 +46,18 @@ int devfs_partition_complete(struct string_list *sl, char *instr)
 }
 #endif
 
-struct cdev *cdev_by_name(const char *filename)
+struct cdev *cdev_readlink(struct cdev *cdev)
+{
+	if (cdev->link)
+		cdev = cdev->link;
+
+	/* links to links are not allowed */
+	BUG_ON(cdev->link);
+
+	return cdev;
+}
+
+struct cdev *lcdev_by_name(const char *filename)
 {
 	struct cdev *cdev;
 
@@ -57,6 +68,17 @@ struct cdev *cdev_by_name(const char *filename)
 	return NULL;
 }
 
+struct cdev *cdev_by_name(const char *filename)
+{
+	struct cdev *cdev;
+
+	cdev = lcdev_by_name(filename);
+	if (!cdev)
+		return NULL;
+
+	return cdev_readlink(cdev);
+}
+
 struct cdev *cdev_by_device_node(struct device_node *node)
 {
 	struct cdev *cdev;
@@ -65,7 +87,7 @@ struct cdev *cdev_by_device_node(struct device_node *node)
 		if (!cdev->device_node)
 			continue;
 		if (cdev->device_node == node)
-			return cdev;
+			return cdev_readlink(cdev);
 	}
 	return NULL;
 }
@@ -111,14 +133,6 @@ int cdev_find_free_index(const char *basename)
 	return -EBUSY;	/* all indexes are used */
 }
 
-int cdev_do_open(struct cdev *cdev, unsigned long flags)
-{
-	if (cdev->ops->open)
-		return cdev->ops->open(cdev, flags);
-
-	return 0;
-}
-
 struct cdev *cdev_open(const char *name, unsigned long flags)
 {
 	struct cdev *cdev;
@@ -131,9 +145,11 @@ struct cdev *cdev_open(const char *name, unsigned long flags)
 	if (!cdev)
 		return NULL;
 
-	ret = cdev_do_open(cdev, flags);
-	if (ret)
-		return NULL;
+	if (cdev->ops->open) {
+		ret = cdev->ops->open(cdev, flags);
+		if (ret)
+			return NULL;
+	}
 
 	return cdev;
 }
@@ -266,8 +282,31 @@ int devfs_create(struct cdev *new)
 	return 0;
 }
 
+int devfs_create_link(struct cdev *cdev, const char *name)
+{
+	struct cdev *new;
+
+	if (cdev_by_name(name))
+		return -EEXIST;
+
+	/*
+	 * Create a link to the real cdev instead of creating
+	 * a link to a link.
+	 */
+	cdev = cdev_readlink(cdev);
+
+	new = xzalloc(sizeof(*new));
+	new->name = xstrdup(name);
+	new->link = cdev;
+	list_add_tail(&new->list, &cdev_list);
+
+	return 0;
+}
+
 int devfs_remove(struct cdev *cdev)
 {
+	struct cdev *c, *tmp;
+
 	if (cdev->open)
 		return -EBUSY;
 
@@ -275,6 +314,13 @@ int devfs_remove(struct cdev *cdev)
 	if (cdev->dev)
 		list_del(&cdev->devices_list);
 
+	list_for_each_entry_safe(c, tmp, &cdev_list, list)
+		if (c->link == cdev)
+			devfs_remove(c);
+
+	if (cdev->link)
+		free(cdev);
+
 	return 0;
 }
 
diff --git a/fs/devfs.c b/fs/devfs.c
index 5c96682..0b8d4fd 100644
--- a/fs/devfs.c
+++ b/fs/devfs.c
@@ -212,12 +212,18 @@ static int devfs_stat(struct device_d *_dev, const char *filename, struct stat *
 {
 	struct cdev *cdev;
 
-	cdev = cdev_by_name(filename + 1);
+	cdev = lcdev_by_name(filename + 1);
 	if (!cdev)
 		return -ENOENT;
 
 	s->st_mode = S_IFCHR;
 	s->st_size = cdev->size;
+
+	if (cdev->link)
+		s->st_mode |= S_IFLNK;
+
+	cdev = cdev_readlink(cdev);
+
 	if (cdev->ops->write)
 		s->st_mode |= S_IWUSR;
 	if (cdev->ops->read)
@@ -242,6 +248,24 @@ static void devfs_delete(struct device_d *dev)
 {
 }
 
+static int devfs_readlink(struct device_d *dev, const char *pathname,
+			  char *buf, size_t bufsz)
+{
+	struct cdev *cdev;
+
+	cdev = cdev_by_name(pathname + 1);
+	if (!cdev)
+		return -ENOENT;
+
+	while (cdev->link)
+		cdev = cdev->link;
+
+	bufsz = min(bufsz, strlen(cdev->name));
+	memcpy(buf, cdev->name, bufsz);
+
+	return 0;
+}
+
 static struct fs_driver_d devfs_driver = {
 	.read      = devfs_read,
 	.write     = devfs_write,
@@ -258,6 +282,7 @@ static struct fs_driver_d devfs_driver = {
 	.erase     = devfs_erase,
 	.protect   = devfs_protect,
 	.memmap    = devfs_memmap,
+	.readlink  = devfs_readlink,
 	.flags     = FS_DRIVER_NO_DEV,
 	.drv = {
 		.probe  = devfs_probe,
diff --git a/include/driver.h b/include/driver.h
index 046dd90..29686f5 100644
--- a/include/driver.h
+++ b/include/driver.h
@@ -450,13 +450,17 @@ struct cdev {
 	int open;
 	struct mtd_info *mtd;
 	u8 dos_partition_type;
+	struct cdev *link;
 };
 
 int devfs_create(struct cdev *);
+int devfs_create_link(struct cdev *, const char *name);
 int devfs_remove(struct cdev *);
 int cdev_find_free_index(const char *);
 struct cdev *device_find_partition(struct device_d *dev, const char *name);
 struct cdev *cdev_by_name(const char *filename);
+struct cdev *lcdev_by_name(const char *filename);
+struct cdev *cdev_readlink(struct cdev *cdev);
 struct cdev *cdev_by_device_node(struct device_node *node);
 struct cdev *cdev_open(const char *name, unsigned long flags);
 int cdev_do_open(struct cdev *, unsigned long flags);
-- 
2.6.2