Re: [PATCH v2 13/22] coredump: add COREDUMP_RECORDS to the coredump socket protocol

[R Nageswara Sastry <rnsastry@linux.ibm.com>]

On 20.08.2026 4:39 AM, Christian Brauner wrote:
> Currently a coredump sent over a socket is raw data. The kernel knows
> things about the data it's sending that are useful for a coredump
> server. For example, it knows where the unpopulated parts of a mapping
> are. We can't communicate this to userspace currently though.
>
> Add a COREDUMP_RECORDS feature bit and a struct coredump_record_header
> so userspace can negotiate that feature. Instead of a byte stream it
> gets a header plus data. Reassembling the records yields the same
> coredump that would have been sent without them.
>
> The record itself is also versioned and thus extensible with the same
> protocol as the ack-req sync.
>
> A record stream ends explicitly. A COREDUMP_RECORD_END record closes it,
> carries no data and reports the size of the coredump. It is only sent
> once the whole coredump has been written. If it's missing the coredump
> should be treated as truncated.
>
> This just adds the infrastructure.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>

System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2

> ---
>   include/uapi/linux/coredump.h | 66 +++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 66 insertions(+)
>
> diff --git a/include/uapi/linux/coredump.h b/include/uapi/linux/coredump.h
> index 662e0468da6e..0bd5c8662ebe 100644
> --- a/include/uapi/linux/coredump.h
> +++ b/include/uapi/linux/coredump.h
> @@ -11,12 +11,16 @@
>    * @COREDUMP_USERSPACE: userspace writes coredump
>    * @COREDUMP_REJECT: don't generate coredump
>    * @COREDUMP_WAIT: wait for coredump server
> + * @COREDUMP_RECORDS: send the coredump as a sequence of records instead of
> + *                    as a plain byte stream, see struct coredump_record_header;
> + *                    requires COREDUMP_KERNEL
>    */
>   enum {
>   	COREDUMP_KERNEL		= (1ULL << 0),
>   	COREDUMP_USERSPACE	= (1ULL << 1),
>   	COREDUMP_REJECT		= (1ULL << 2),
>   	COREDUMP_WAIT		= (1ULL << 3),
> +	COREDUMP_RECORDS	= (1ULL << 4),
>   };
>   
>   /**
> @@ -101,4 +105,66 @@ enum coredump_mark {
>   	__COREDUMP_MARK_MAX		= (1U << 31),
>   };
>   
> +/**
> + * enum coredump_record_type - Type of a coredump record
> + *
> + * @COREDUMP_RECORD_DATA: the header is followed by ->len bytes of data
> + * @COREDUMP_RECORD_END: the coredump ends here, the header is not followed
> + *                       by any data and no further record is sent
> + * @__COREDUMP_RECORD_TYPE_MAX: the maximum coredump record type value
> + */
> +enum coredump_record_type {
> +	COREDUMP_RECORD_DATA		= 0U,
> +	COREDUMP_RECORD_END		= 1U,
> +	__COREDUMP_RECORD_TYPE_MAX	= (1U << 31),
> +};
> +
> +/**
> + * struct coredump_record_header - header of a coredump record
> + * @size: size of struct coredump_record_header
> + * @type: one of enum coredump_record_type
> + * @flags: modifiers for this record
> + * @offset: offset in the coredump this record starts at
> + * @len: number of coredump bytes this record accounts for
> + *
> + * If the coredump server raises COREDUMP_RECORDS in coredump_ack->mask
> + * the kernel doesn't send the coredump as a plain byte stream. It sends
> + * a sequence of records instead. A COREDUMP_RECORD_DATA record is
> + * followed by @len bytes of actual coredump data. Records arrive in
> + * order and leave no gaps. So @offset is the sum of the @len of all
> + * records before it.
> + *
> + * The last record is a COREDUMP_RECORD_END record. It is followed by
> + * nothing. Its @len is zero. Its @offset is the size of the coredump.
> + * The kernel only sends it once it has written the whole coredump. A
> + * server that hits end-of-file without having seen an end record must
> + * treat the coredump as incomplete.
> + *
> + * The @size member is set to the size of struct coredump_record_header
> + * the kernel knows and lets the header grow later. It comes first so it
> + * can be peeked. Userspace must consume @size bytes and discard
> + * anything beyond what it knows. It must refuse a @size smaller than
> + * COREDUMP_RECORD_HEADER_SIZE_VER0. @size covers the header alone.
> + * @offset and @len count coredump bytes.
> + *
> + * The @flags member carries modifiers that change how the record is to
> + * be interpreted. No flag is defined yet. Userspace must refuse a
> + * record carrying a flag or a type it doesn't know. Every new record
> + * type is raised in coredump_req->mask as a feature of its own. A
> + * server only ever sees the types it asked for.
> + *
> + * COREDUMP_RECORDS must be combined with COREDUMP_KERNEL.
> + */
> +struct coredump_record_header {
> +	__u32 size;
> +	__u32 type;
> +	__u64 flags;
> +	__u64 offset;
> +	__u64 len;
> +};
> +
> +enum {
> +	COREDUMP_RECORD_HEADER_SIZE_VER0 = 32U, /* size of first published struct */
> +};
> +
>   #endif /* _UAPI_LINUX_COREDUMP_H */
>
-- 
Thanks and Regards
R.Nageswara Sastry