Re: [PATCH v2 19/22] selftests/coredump: hand the record stream to a sink

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

On 20.08.2026 4:39 AM, Christian Brauner wrote:
> Currently recv_coredump_records() parses the record stream and dumps it
> into a file. A coredump server may want to process the data it gets. So
> split the parsing from the processing.
>
> No functional changes.
>
> 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
> ---
>   .../selftests/coredump/coredump_test_helpers.c     | 91 +++++++++++++++++-----
>   1 file changed, 72 insertions(+), 19 deletions(-)
>
> diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c
> index 5b2ffe17f7b7..45d76fa0f469 100644
> --- a/tools/testing/selftests/coredump/coredump_test_helpers.c
> +++ b/tools/testing/selftests/coredump/coredump_test_helpers.c
> @@ -71,9 +71,19 @@ void crashing_child_sparse(size_t size)
>   	*(volatile int *)NULL = 0;
>   }
>   
> -/* Read @len bytes off the socket, writing them at @offset if @fd_out >= 0. */
> -static ssize_t recv_record_bytes(int fd_coredump, __u64 len, int fd_out,
> -				 off_t offset)
> +/* Sink a reassembled record stream is handed to, record by record. */
> +struct coredump_record_sink {
> +	/* @len bytes of coredump data that belong at @offset. */
> +	int (*data)(void *ctx, const void *buf, size_t len, __u64 offset);
> +	/* @len zero bytes that belong at @offset. */
> +	int (*zero)(void *ctx, __u64 offset, __u64 len);
> +	void *ctx;
> +};
> +
> +/* Read @len bytes off the socket and hand them to @sink, if there is one. */
> +static ssize_t recv_record_bytes(int fd_coredump, __u64 len,
> +				 const struct coredump_record_sink *sink,
> +				 __u64 offset)
>   {
>   	ssize_t received = 0;
>   
> @@ -89,11 +99,8 @@ static ssize_t recv_record_bytes(int fd_coredump, __u64 len, int fd_out,
>   			return -1;
>   		}
>   
> -		if (fd_out >= 0 &&
> -		    pwrite(fd_out, buffer, ret, offset + received) != ret) {
> -			fprintf(stderr, "%s: pwrite failed: %m\n", __func__);
> +		if (sink && sink->data(sink->ctx, buffer, ret, offset + received))
>   			return -1;
> -		}
>   
>   		received += ret;
>   		len -= ret;
> @@ -102,14 +109,34 @@ static ssize_t recv_record_bytes(int fd_coredump, __u64 len, int fd_out,
>   	return received;
>   }
>   
> +/* Put the data where the records say it goes and leave the holes alone. */
> +static int file_sink_data(void *ctx, const void *buf, size_t len, __u64 offset)
> +{
> +	int fd = *(int *)ctx;
> +
> +	if (pwrite(fd, buf, len, offset) != (ssize_t)len) {
> +		fprintf(stderr, "%s: pwrite failed: %m\n", __func__);
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
> +static int file_sink_zero(void *ctx, __u64 offset, __u64 len)
> +{
> +	/* Nothing has to be written for a hole. */
> +	return 0;
> +}
> +
>   /*
> - * Reassemble a record stream. If @fd_peer_pidfd is valid the task behind
> - * it is killed once a data record has arrived, so the kernel has to cut
> - * the coredump short with the stream already under way.
> + * Read a coredump strea and funnel it into @sink. Allow to pass in a
> + * @fd_peer_pidfd to simulate coredump truncation by killing it after having
> + * received a coredump record.
>    */
> -ssize_t recv_coredump_records(int fd_coredump, int fd_core_file,
> -			      off_t *coredump_size, bool *truncated,
> -			      int fd_peer_pidfd)
> +static ssize_t __recv_coredump_records(int fd_coredump,
> +				       const struct coredump_record_sink *sink,
> +				       off_t *coredump_size, bool *truncated,
> +				       int fd_peer_pidfd)
>   {
>   	ssize_t received = 0;
>   	off_t size = 0;
> @@ -169,7 +196,8 @@ ssize_t recv_coredump_records(int fd_coredump, int fd_core_file,
>   		}
>   
>   		/* Discard any part of the header we have no use for. */
> -		ret = recv_record_bytes(fd_coredump, record.size - known_size, -1, 0);
> +		ret = recv_record_bytes(fd_coredump, record.size - known_size,
> +					NULL, 0);
>   		if (ret < 0)
>   			return -1;
>   		received += ret;
> @@ -185,10 +213,12 @@ ssize_t recv_coredump_records(int fd_coredump, int fd_core_file,
>   		switch (record.type) {
>   		case COREDUMP_RECORD_ZERO:
>   			/* A hole. It comes with no data and needs none. */
> +			if (sink->zero(sink->ctx, record.offset, record.len))
> +				return -1;
>   			break;
>   		case COREDUMP_RECORD_DATA:
> -			ret = recv_record_bytes(fd_coredump, record.len,
> -						fd_core_file, size);
> +			ret = recv_record_bytes(fd_coredump, record.len, sink,
> +						record.offset);
>   			if (ret < 0)
>   				return -1;
>   			received += ret;
> @@ -230,6 +260,32 @@ ssize_t recv_coredump_records(int fd_coredump, int fd_core_file,
>   	if (truncated)
>   		*truncated = is_truncated;
>   
> +	*coredump_size = size;
> +
> +	fprintf(stderr, "Received %zd bytes for a %s coredump of %llu bytes\n",
> +		received, is_truncated ? "truncated" : "complete",
> +		(unsigned long long)size);
> +	return received;
> +}
> +
> +/* Reassemble a record stream into the coredump it describes. */
> +ssize_t recv_coredump_records(int fd_coredump, int fd_core_file,
> +			      off_t *coredump_size, bool *truncated,
> +			      int fd_peer_pidfd)
> +{
> +	struct coredump_record_sink sink = {
> +		.data	= file_sink_data,
> +		.zero	= file_sink_zero,
> +		.ctx	= &fd_core_file,
> +	};
> +	ssize_t received;
> +	off_t size = 0;
> +
> +	received = __recv_coredump_records(fd_coredump, &sink, &size, truncated,
> +					   fd_peer_pidfd);
> +	if (received < 0)
> +		return -1;
> +
>   	/*
>   	 * Nothing is written for a hole, so grow the file to the size the
>   	 * records describe in case the coredump ended in one.
> @@ -243,9 +299,6 @@ ssize_t recv_coredump_records(int fd_coredump, int fd_core_file,
>   	if (coredump_size)
>   		*coredump_size = size;
>   
> -	fprintf(stderr, "Received %zd bytes for a %s coredump of %llu bytes\n",
> -		received, is_truncated ? "truncated" : "complete",
> -		(unsigned long long)size);
>   	return received;
>   }
>   
>
-- 
Thanks and Regards
R.Nageswara Sastry