[PATCH] cdev: maintain partition index in struct cdev

[Sascha Hauer]

On Thu, Dec 18, 2025 at 10:30:59AM +0100, Ahmad Fatoum wrote:
> 
> 
> On 12/18/25 10:29 AM, Sascha Hauer wrote:
> > 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?
> 
> Yes, of course. Should I resend?

Nope, fixed.

Sascha

> 
> > 
> > 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
> >>
> >>
> >>
> > 
> 
> -- 
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> 
> 

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Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
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