Re: [PATCH RFC v1] rds: Expose feature parameters via sysfs and ELF note

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Jun 10, 2025 at 12:27:25PM -0400, Konrad Rzeszutek Wilk wrote:

Hi!
I've added some extra folks on the To: list to solicit feedback on this
idea since something similar was done via

3958e2d0c34e1 cgroup: make per-cgroup pressure stall tracking configurable
01ee6cfb1483f cgroup: export list of delegatable control files using sysfs
5f2e673405b74 cgroup: export list of cgroups v2 features using sysfs

Thank you for you time!
> We would like to have a programatic way for applications
> to query which of the features defined in include/uapi/linux/rds.h
> are actually implemented by the kernel.
> 
> The problem is that applications can be built against newer
> kernel (or older) and they may have the feature implemented or not.
> 
> The lack of a certain feature would signify that the kernel
> does not support it. The presence of it signifies the existence
> of it.
> 
> This would provide the application to query the sysfs and figure
> out what is supported (and which ones are deprecated) and also
> what ioctl number to use for the specific feature (albeit that
> is already in include/uapi/linux/rds.h but this is an extra
> check if someone messed up).
> 
> This patch would expose these extra sysfs values:
> 
> /sys/module/rds/parameters/rds_ioctl_get_tos: 35297
> /sys/module/rds/parameters/rds_ioctl_set_tos: 35296
> /sys/module/rds/parameters/rds_socket_cancel_sent_to: 1
> /sys/module/rds/parameters/rds_socket_cong_monitor: 6
> /sys/module/rds/parameters/rds_socket_free_mr: 3
> /sys/module/rds/parameters/rds_socket_get_mr: 2
> /sys/module/rds/parameters/rds_socket_get_mr_for_dest: 7
> /sys/module/rds/parameters/rds_socket_recverr: 5
> /sys/module/rds/parameters/rds_socket_so_rxpath_latency: 9
> /sys/module/rds/parameters/rds_socket_so_transport: 8
> /sys/module/rds/parameters/rds_so_transport_ib: 0
> /sys/module/rds/parameters/rds_so_transport_tcp: 2
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
>  Documentation/ABI/stable/sysfs-driver-rds | 92 +++++++++++++++++++++++
>  net/rds/af_rds.c                          | 33 ++++++++
>  2 files changed, 125 insertions(+)
>  create mode 100644 Documentation/ABI/stable/sysfs-driver-rds
> 
> diff --git a/Documentation/ABI/stable/sysfs-driver-rds b/Documentation/ABI/stable/sysfs-driver-rds
> new file mode 100644
> index 000000000000..dcb1a335c5d6
> --- /dev/null
> +++ b/Documentation/ABI/stable/sysfs-driver-rds
> @@ -0,0 +1,92 @@
> +What:		/sys/module/rds/parameters/rds_ioctl_set_tos
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports the mechanism to set on a socket
> +		the Quality of Service.
> +
> +		The returned value is the socket ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_ioctl_get_tos
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports the mechanism to get on a socket
> +		the Quality of Service.
> +
> +		The returned value is the socket ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_cancel_sent_to
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports the mechanism to cancel all pending
> +		messages to a given destination.
> +
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_get_mr
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports the mechanism to retrieve the memory
> +		ranges for the RDMA calls to setsockopt.
> +
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_free_mr
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports the mechanism to release the memory
> +		ranges for the RDMA calls to setsockopt.
> +
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_recverr
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports the mechanism to send RDMA notifications
> +		for any RDMA operation that fails.
> +
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_cong_monitor
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The RDS driver supports mechanism to provide Congestion updates via
> +		RDS_CMSG_CONG_UPDATE control messages.
> +
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_get_mr_for_dest
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_so_transport
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_socket_so_rxpath_latency
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The returned value is the ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_so_transport_ib
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The returned value for the IB transport ioctl number and this is read-only.
> +
> +What:		/sys/module/rds/parameters/rds_so_transport_tcp
> +Date:		Jun 2025
> +Contact:	rds-devel@oss.oracle.com
> +Description:
> +		The returned value is the TCP transport number and this is read-only.
> diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
> index 8435a20968ef..15c8ded02dfb 100644
> --- a/net/rds/af_rds.c
> +++ b/net/rds/af_rds.c
> @@ -31,6 +31,7 @@
>   *
>   */
>  #include <linux/module.h>
> +#include <linux/elfnote.h>
>  #include <linux/errno.h>
>  #include <linux/kernel.h>
>  #include <linux/gfp.h>
> @@ -960,3 +961,35 @@ MODULE_DESCRIPTION("RDS: Reliable Datagram Sockets"
>  MODULE_VERSION(DRV_VERSION);
>  MODULE_LICENSE("Dual BSD/GPL");
>  MODULE_ALIAS_NETPROTO(PF_RDS);
> +
> +#define RDS_IOCTL(feature, val) ELFNOTE64("rds.ioctl_" #feature, 0, val); \
> +				unsigned int rds_ioctl_##feature = val; \
> +				module_param(rds_ioctl_##feature, int, 0444)
> +
> +#define RDS_SOCKET(feature, val) ELFNOTE64("rds.socket_" #feature, 0, val); \
> +				unsigned int rds_socket_##feature = val; \
> +				module_param(rds_socket_##feature, int, 0444)
> +
> +#define RDS_SO_TRANSPORT(feature, val) ELFNOTE64("rds.so_transport_" #feature, 0, val); \
> +				unsigned int rds_so_transport_##feature = val; \
> +				module_param(rds_so_transport_##feature, int, 0444)
> +
> +/* The values used here correspond to include/uapi/linux/rds.h values */
> +
> +RDS_IOCTL(set_tos, SIOCRDSSETTOS);
> +RDS_IOCTL(get_tos, SIOCRDSGETTOS);
> +
> +/* Advertise setsocket/getsocket options. */
> +
> +RDS_SOCKET(cancel_sent_to, RDS_CANCEL_SENT_TO);
> +RDS_SOCKET(get_mr, RDS_GET_MR);
> +RDS_SOCKET(free_mr, RDS_FREE_MR);
> +RDS_SOCKET(recverr, RDS_RECVERR);
> +RDS_SOCKET(cong_monitor, RDS_CONG_MONITOR);
> +RDS_SOCKET(get_mr_for_dest, RDS_GET_MR_FOR_DEST);
> +RDS_SOCKET(so_transport, SO_RDS_TRANSPORT);
> +RDS_SOCKET(so_rxpath_latency, SO_RDS_MSG_RXPATH_LATENCY);
> +
> +/* The transport mechanisms. */
> +RDS_SO_TRANSPORT(ib, RDS_TRANS_IB);
> +RDS_SO_TRANSPORT(tcp, RDS_TRANS_TCP);
> -- 
> 2.43.5
>