[PATCH] cdev: maintain partition index in struct cdev

[Sascha Hauer]

On Thu, Dec 18, 2025 at 10:19:45AM +0100, Ahmad Fatoum wrote:
> For use by the EFI loader, we will need to know a partition's number
> within the partition table on disk, so have the devfs-core keep track
> of that.
> 
> Mere iteration over the cdev list doesn't work for thus purpose as there
> may be invalid PTEs, which cause e.g. the first on-disk partition to
> have a higher number.
> 
> See 9dfffaf2ef47 ("partitions: efi: Continue partition enumeration on
> invalid pte") for more info. A real world example is the current
> debian-13-nocloud-arm64.raw image, which has two partitions:
> 0 and 14 (or 1 and 15 in barebox).

Should have mentioned this in my last mail, but isn't this the other way
round?

Sascja

> 
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
> v2 -> v3:
>   - fix comment to mention that index is 0-based (Sascha)j
> v1 -> v2:
>   - record actual partition number from the table.
>     I compared against EDK-II and Linux and both take the actual
>     number, which may not be either the number in our cdev list
>     or the location on disk.
> ---
>  common/partitions.c | 1 +
>  include/driver.h    | 3 +++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/common/partitions.c b/common/partitions.c
> index 1a4e046c5f55..40f4c629e1ac 100644
> --- a/common/partitions.c
> +++ b/common/partitions.c
> @@ -52,6 +52,7 @@ static int register_one_partition(struct block_device *blk, struct partition *pa
>  		goto out;
>  	}
>  
> +	cdev->partition_table_index = part->num;
>  	cdev->flags |= DEVFS_PARTITION_FROM_TABLE | part->flags;
>  	cdev->typeflags |= part->typeflags;
>  	cdev->typeuuid = part->typeuuid;
> diff --git a/include/driver.h b/include/driver.h
> index 14d1731fd976..77b9b876955a 100644
> --- a/include/driver.h
> +++ b/include/driver.h
> @@ -436,6 +436,9 @@ struct cdev {
>  	loff_t size;
>  	unsigned int flags;
>  	u16 typeflags; /* GPT type-specific attributes */
> +	s8 partition_table_index;    /* For GPT/MBR-formatted disks only:
> +				      * 0-based index of partition on disk
> +				      */
>  	int open;
>  	struct mtd_info *mtd;
>  	struct list_head aliases;
> -- 
> 2.47.3
> 
> 
> 

-- 
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 |