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

[Sascha Hauer <s.hauer@pengutronix.de>]

On Mon, Dec 15, 2025 at 12:31:50PM +0100, Ahmad Fatoum wrote:
> Hi,
> 
> On 12/9/25 1:51 PM, Sascha Hauer wrote:
> 
> A commit message would be grand. :)

Added one and also integrated the other changes you suggested, thanks
Ahamd.

Sascha

> 
> > 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);
> > 
> 
> -- 
> Pengutronix e.K.                  |                             |
> Steuerwalder Str. 21              | http://www.pengutronix.de/  |
> 31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |
> 
> 

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |