Re: [PATCH v2 12/13] fs: replace cdev links with aliases

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi,

On 12/9/25 1:51 PM, Sascha Hauer wrote:

A commit message would be grand. :)

> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Acked-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

> ---
>  commands/devinfo.c              |   7 +-
>  common/partitions.c             |   2 +-
>  drivers/block/dm/dm-core.c      |   1 -
>  drivers/misc/storage-by-alias.c |   2 +-
>  fs/devfs-core.c                 | 191 +++++++++++++++++++++-------------------
>  include/block.h                 |   2 -
>  include/driver.h                |  20 +++--
>  7 files changed, 121 insertions(+), 104 deletions(-)
> 
> diff --git a/commands/devinfo.c b/commands/devinfo.c
> index c87b30e84307e5053bc35e8bd70ac7af63f688b8..c5417cb7bbe9c7beacd85888fb34405bdc279aea 100644
> --- a/commands/devinfo.c
> +++ b/commands/devinfo.c
> @@ -9,7 +9,8 @@
>  static int do_devinfo_subtree(struct device *dev, int depth)
>  {
>  	struct device *child;
> -	struct cdev *cdev, *cdevl;
> +	struct cdev *cdev;
> +	struct cdev_alias *alias;
>  	int i;
>  
>  	for (i = 0; i < depth; i++)
> @@ -26,8 +27,8 @@ static int do_devinfo_subtree(struct device *dev, int depth)
>  					cdev->offset + cdev->size - 1,
>  					size_human_readable(cdev->size),
>  					cdev->name);
> -			list_for_each_entry(cdevl, &cdev->links, link_entry)
> -				printf(", %s", cdevl->name);
> +			cdev_for_each_alias(alias, cdev)
> +				printf(", %s", alias->name);
>  			printf("\n");
>  		}
>  	} else {
> diff --git a/common/partitions.c b/common/partitions.c
> index 7563cb0e6767891ee7f1fe264ce86703408f790a..1a4e046c5f55314ccb2abf5094b0966def8c5b55 100644
> --- a/common/partitions.c
> +++ b/common/partitions.c
> @@ -63,7 +63,7 @@ static int register_one_partition(struct block_device *blk, struct partition *pa
>  		return 0;
>  
>  	partition_name = xasprintf("%s.%s", blk->cdev.name, part->name);
> -	ret = devfs_create_link(cdev, partition_name);
> +	ret = devfs_add_alias(cdev, partition_name);
>  	if (ret)
>  		dev_warn(blk->dev, "Failed to create link from %s to %s\n",
>  			 partition_name, cdev->name);
> diff --git a/drivers/block/dm/dm-core.c b/drivers/block/dm/dm-core.c
> index fd7ed0d84ed7388f8c1cd4aa19e0466191459fd6..2f48cfeb06f7b2da6d26850820f228a6f522fc2f 100644
> --- a/drivers/block/dm/dm-core.c
> +++ b/drivers/block/dm/dm-core.c
> @@ -77,7 +77,6 @@ int dm_cdev_open(struct dm_cdev *dmcdev, const char *path, ulong flags,
>  			return -ENODEV;
>  		}
>  
> -		dmcdev->cdev = cdev_readlink(dmcdev->cdev);
>  		break;
>  	default:
>  		*errmsg = xstrdup("Only regular files and device specials are supported");
> diff --git a/drivers/misc/storage-by-alias.c b/drivers/misc/storage-by-alias.c
> index 6c759867ccbb7a7b4bc922152699eb346d42d271..196346c8eafcc7868aa279353414409617e1e907 100644
> --- a/drivers/misc/storage-by-alias.c
> +++ b/drivers/misc/storage-by-alias.c
> @@ -38,7 +38,7 @@ static int sba_add_partitions(struct cdev *rcdev, void *data)
>  
>  	dev_info(sba->dev, "Adding %s -> %s\n", sba->alias, rcdev->name);
>  
> -	ret = devfs_create_link_node(rcdev, sba->alias, sba->dev->device_node);
> +	ret = devfs_add_alias_node(rcdev, sba->alias, sba->dev->device_node);
>  	if (ret)
>  		return ret;
>  
> diff --git a/fs/devfs-core.c b/fs/devfs-core.c
> index 3a5667b9f723fa718453bdc58827f4b760f3565a..b285b7ede029b14bb0bbc1dbf60ba8a8895c3f26 100644
> --- a/fs/devfs-core.c
> +++ b/fs/devfs-core.c
> @@ -50,42 +50,21 @@ int devfs_partition_complete(struct string_list *sl, char *instr)
>  }
>  #endif
>  
> -struct cdev *cdev_readlink(const struct cdev *cdev)
> -{
> -	if (!cdev)
> -		return NULL;
> -
> -	if (cdev->link)
> -		cdev = cdev->link;
> -
> -	/* links to links are not allowed */
> -	BUG_ON(cdev->link);
> -
> -	return (void *)cdev;
> -}
> -
> -struct cdev *lcdev_by_name(const char *filename)
> +struct cdev *cdev_by_name(const char *filename)
>  {
>  	struct cdev *cdev;
> +	struct cdev_alias *alias;
>  
>  	for_each_cdev(cdev) {
>  		if (!strcmp(cdev->name, filename))
>  			return cdev;
> +		cdev_for_each_alias(alias, cdev)
> +			if (!strcmp(alias->name, filename))
> +				return cdev;
>  	}
>  	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;
> @@ -94,8 +73,14 @@ struct cdev *cdev_by_device_node(struct device_node *node)
>  		return NULL;
>  
>  	for_each_cdev(cdev) {
> +		struct cdev_alias *alias;
> +
>  		if (cdev_of_node(cdev) == node)
> -			return cdev_readlink(cdev);
> +			return cdev;
> +
> +		cdev_for_each_alias(alias, cdev)
> +			if (alias->device_node == node)
> +				return cdev;
>  	}
>  	return NULL;
>  }
> @@ -133,9 +118,6 @@ cdev_find_child_by_gpt_typeuuid(struct cdev *cdev, const guid_t *typeuuid)
>  {
>  	struct cdev *partcdev;
>  
> -        /* Follow links to support storage-by-alias */
> -        cdev = cdev_readlink(cdev);
> -
>  	if (!cdev_is_gpt_partitioned(cdev))
>  		return ERR_PTR(-EINVAL);
>  
> @@ -153,6 +135,29 @@ cdev_find_child_by_gpt_typeuuid(struct cdev *cdev, const guid_t *typeuuid)
>  	return ERR_PTR(-ENOENT);
>  }
>  
> +static bool cdev_has_partname_alias(struct cdev *cdev, const char *partname)
> +{
> +	char *fullname;
> +	struct cdev_alias *alias;
> +	bool ret = false;
> +
> +	if (!cdev->master)
> +		return false;
> +
> +	fullname = xasprintf("%s.%s", cdev->master->name, partname);
> +
> +	cdev_for_each_alias(alias, cdev) {
> +		if (streq_ptr(alias->name, fullname)) {
> +			ret = true;
> +			break;
> +		}
> +	}
> +
> +	free(fullname);
> +
> +	return ret;
> +}
> +
>  /**
>   * cdev_find_partition - find a partition belonging to a physical device
>   *
> @@ -164,15 +169,10 @@ struct cdev *cdev_find_partition(struct cdev *cdevm, const char *name)
>  	struct cdev *partcdev;
>  
>  	for_each_cdev_partition(partcdev, cdevm) {
> -		struct cdev *cdevl;
> -
>  		if (streq_ptr(partcdev->partname, name))
>  			return partcdev;
> -
> -		list_for_each_entry(cdevl, &partcdev->links, link_entry) {
> -			if (streq_ptr(cdevl->partname, name))
> -				return cdevl;
> -		}
> +		if (cdev_has_partname_alias(partcdev, name))
> +			return partcdev;
>  	}
>  
>  	return NULL;
> @@ -190,15 +190,11 @@ struct cdev *device_find_partition(struct device *dev, const char *name)
>  	struct device *child;
>  
>  	list_for_each_entry(cdev, &dev->cdevs, devices_list) {
> -		struct cdev *cdevl;
> -
>  		if (streq_ptr(cdev->partname, name))
>  			return cdev;
>  
> -		list_for_each_entry(cdevl, &cdev->links, link_entry) {
> -			if (streq_ptr(cdevl->partname, name))
> -				return cdev_readlink(cdevl);
> -		}
> +		if (cdev_has_partname_alias(cdev, name))
> +			return cdev;
>  	}
>  
>  	device_for_each_child(dev, child) {
> @@ -460,25 +456,54 @@ static void cdev_free(struct cdev *cdev)
>  
>  static bool devfs_initialized;
>  
> +static int cdev_symlink(struct cdev *cdev, const char *linkname)
> +{
> +	char *path;
> +	int ret;
> +
> +	if (!devfs_initialized)
> +		return 0;
> +
> +	path = xasprintf("/dev/%s", linkname);
> +	ret = symlink(cdev->name, path);
> +	free(path);
> +
> +	return ret;
> +}
> +
>  static void devfs_mknod(struct cdev *cdev)
>  {
>  	char *path;
>  	int ret;
> +	struct cdev_alias *alias;
>  
>  	if (!devfs_initialized)
>  		return;
>  
>  	path = xasprintf("/dev/%s", cdev->name);
>  
> -	if (cdev->link)
> -		ret = symlink(cdev->link->name, path);
> -	else
> -		ret = mknod(path, S_IFCHR | 0600, cdev->name);
> +	cdev_for_each_alias(alias, cdev)
> +		cdev_symlink(cdev, alias->name);
> +
> +	ret = mknod(path, S_IFCHR | 0600, cdev->name);
>  
>  	free(path);
>  
> -	if (ret)
> +	if (ret) {
>  		pr_err("Failed to create /dev/%s: %pe\n", cdev->name, ERR_PTR(ret));
> +		dump_stack();
> +	}
> +}
> +
> +static void devfs_unlink(const char *name)
> +{
> +	char *path;
> +
> +	path = xasprintf("/dev/%s", name);
> +
> +	unlink(path);
> +
> +	free(path);
>  }
>  
>  void devfs_init(void)
> @@ -499,8 +524,8 @@ int devfs_create(struct cdev *new)
>  	if (cdev)
>  		return -EEXIST;
>  
> -	INIT_LIST_HEAD(&new->links);
>  	INIT_LIST_HEAD(&new->partitions);
> +	INIT_LIST_HEAD(&new->aliases);
>  
>  	list_add_tail(&new->list, &cdev_list);
>  	if (new->dev) {
> @@ -509,54 +534,44 @@ int devfs_create(struct cdev *new)
>  			new->device_node = new->dev->of_node;
>  	}
>  
> -	if (new->link)
> -		list_add_tail(&new->link_entry, &new->link->links);
> -
>  	devfs_mknod(new);
>  
>  	return 0;
>  }
>  
> -int devfs_create_link_node(struct cdev *cdev, const char *name, struct device_node *node)
> +int devfs_add_alias_node(struct cdev *cdev, const char *name, struct device_node *np)
>  {
> -	struct cdev *new;
> -	int ret;
> -
> -	/*
> -	 * Create a link to the real cdev instead of creating
> -	 * a link to a link.
> -	 */
> -	cdev = cdev_readlink(cdev);
> -
> -	new = cdev_alloc(name);
> -	new->link = cdev;
> -	new->device_node = node;
> -
> -	ret = devfs_create(new);
> -	if (ret) {
> -		cdev_free(new);
> -		return ret;
> -	}
> -
> -	if (cdev->partname) {
> -		size_t partnameoff = 0;
> +	struct cdev *conflict;
> +	struct cdev_alias *alias;
>  
> -		if (cdev->master) {
> -			size_t masterlen = strlen(cdev->master->name);
> +	conflict = cdev_by_name(name);
> +	if (conflict)
> +		return -EEXIST;
>  
> -			if (!strncmp(name, cdev->master->name, masterlen))
> -				partnameoff += masterlen + 1;
> -		}
> +	alias = xzalloc(sizeof(*alias));
> +	alias->name = xstrdup(name);
> +	alias->device_node = np;
> +	list_add_tail(&alias->list, &cdev->aliases);
>  
> -		new->partname = xstrdup(name + partnameoff);
> -	}
> +	cdev_symlink(cdev, name);
>  
>  	return 0;
>  }
>  
> -int devfs_create_link(struct cdev *cdev, const char *name)
> +int devfs_add_alias(struct cdev *cdev, const char *name)
> +{
> +	return devfs_add_alias_node(cdev, name, NULL);
> +}
> +
> +static void devfs_remove_aliases(struct cdev *cdev)
>  {
> -	return devfs_create_link_node(cdev, name, NULL);
> +	struct cdev_alias *alias, *tmp;
> +
> +	list_for_each_entry_safe(alias, tmp, &cdev->aliases, list) {
> +		devfs_unlink(alias->name);
> +		free(alias->name);
> +		free(alias);
> +	}
>  }
>  
>  int devfs_remove(struct cdev *cdev)
> @@ -571,8 +586,9 @@ int devfs_remove(struct cdev *cdev)
>  	if (cdev->dev)
>  		list_del(&cdev->devices_list);
>  
> -	list_for_each_entry_safe(c, tmp, &cdev->links, link_entry)
> -		devfs_remove(c);
> +	devfs_unlink(cdev->name);
> +
> +	devfs_remove_aliases(cdev);
>  
>  	list_for_each_entry_safe(c, tmp, &cdev->partitions, partition_entry)
>  		cdevfs_del_partition(c);
> @@ -580,9 +596,6 @@ int devfs_remove(struct cdev *cdev)
>  	if (cdev_is_partition(cdev))
>  		list_del(&cdev->partition_entry);
>  
> -	if (cdev->link)
> -		cdev_free(cdev);
> -
>  	return 0;
>  }
>  
> @@ -687,7 +700,7 @@ static struct cdev *__devfs_add_partition(struct cdev *cdev,
>  	if (overlap) {
>  		if (!IS_ERR(overlap)) {
>  			/* only fails with -EEXIST, which is fine */
> -			(void)devfs_create_link(overlap, partinfo->name);
> +			(void)devfs_add_alias(overlap, partinfo->name);
>  		}
>  
>  		return overlap;
> diff --git a/include/block.h b/include/block.h
> index fc7a0a32fb2d6bc579aa6305433fb2a9e39f336a..a8ebe202288fff83677948f3d67bc12cae5dc107 100644
> --- a/include/block.h
> +++ b/include/block.h
> @@ -104,13 +104,11 @@ static inline bool cdev_is_block_device(const struct cdev *cdev)
>  
>  static inline bool cdev_is_block_partition(const struct cdev *cdev)
>  {
> -	cdev = cdev_readlink(cdev);
>  	return cdev_is_block_device(cdev) && cdev_is_partition(cdev);
>  }
>  
>  static inline bool cdev_is_block_disk(const struct cdev *cdev)
>  {
> -	cdev = cdev_readlink(cdev);
>  	return cdev_is_block_device(cdev) && !cdev_is_partition(cdev);
>  }
>  
> diff --git a/include/driver.h b/include/driver.h
> index 802917f1c20727272364d094552e4e5b40a6165b..1c78f35f7eb960ac231ee6ad20db8a2a7cbb6a19 100644
> --- a/include/driver.h
> +++ b/include/driver.h
> @@ -17,6 +17,7 @@
>  #include <init.h>
>  #include <errno.h>
>  #include <filetype.h>
> +#include <stringlist.h>
>  
>  #define FORMAT_DRIVER_NAME_ID	"%s%d"
>  
> @@ -432,8 +433,7 @@ struct cdev {
>  	u16 typeflags; /* GPT type-specific attributes */
>  	int open;
>  	struct mtd_info *mtd;
> -	struct cdev *link;
> -	struct list_head link_entry, links;
> +	struct list_head aliases;
>  	struct list_head partition_entry, partitions;
>  	struct cdev *master;
>  	enum filetype filetype;
> @@ -443,6 +443,15 @@ struct cdev {
>  	};
>  };
>  
> +#define cdev_for_each_alias(alias, cdev) \
> +	list_for_each_entry(alias, &cdev->aliases, list)
> +
> +struct cdev_alias {
> +	char *name;
> +	struct device_node *device_node;
> +	struct list_head list;
> +};
> +
>  static inline struct device_node *cdev_of_node(const struct cdev *cdev)
>  {
>  	return IS_ENABLED(CONFIG_OFDEVICE) ? cdev->device_node : NULL;
> @@ -461,15 +470,12 @@ static inline const char *cdev_name(struct cdev *cdev)
>  
>  void devfs_init(void);
>  int devfs_create(struct cdev *);
> -int devfs_create_link(struct cdev *, const char *name);
> -int devfs_create_link_node(struct cdev *cdev, const char *name,
> -			   struct device_node *node);
> +int devfs_add_alias(struct cdev *, const char *name);
> +int devfs_add_alias_node(struct cdev *, const char *name, struct device_node *np);
>  int devfs_remove(struct cdev *);
>  int cdev_find_free_index(const char *);
>  struct cdev *cdev_find_partition(struct cdev *cdevm, const char *name);
>  struct cdev *device_find_partition(struct device *dev, const char *name);
> -struct cdev *lcdev_by_name(const char *filename);
> -struct cdev *cdev_readlink(const struct cdev *cdev);
>  struct cdev *cdev_by_device_node(struct device_node *node);
>  struct cdev *cdev_by_partuuid(const char *partuuid);
>  struct cdev *cdev_by_diskuuid(const char *partuuid);
> 

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