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Alexandra Winter says: ==================== dibs - Direct Internal Buffer Sharing This series introduces a generic abstraction of existing components like: - the s390 specific ISM device (Internal Shared Memory), - the SMC-D loopback mechanism (Shared Memory Communication - Direct) - the client interface of the SMC-D module to the transport devices This generic shim layer can be extended with more devices, more clients and more features in the future. This layer is called 'dibs' for Direct Internal Buffer Sharing based on the common scheme that these mechanisms enable controlled sharing of memory buffers within some containing entity such as a hypervisor or a Linux instance. Benefits: - Cleaner separation of ISM and SMC-D functionality - simpler and less module dependencies - Clear interface definition. - Extendable for future devices and clients. An overview was given at the Netdev 0x19 conference, recordings and slides are available [1]. Background / Status quo: ------------------------ Currently s390 hardware provides virtual PCI ISM devices (Internal Shared Memory). Their driver is in drivers/s390/net/ism_drv.c. The main user is SMC-D (net/smc). The ism driver offers a client interface so other users/protocols can also use them, but it is still heavily intermingled with the smc code. Namely, the ism module cannot be used without the smc module, which feels artificial. There is ongoing work to extend the ISM concept of shared buffers that can be accessed directly by another instance on the same hardware: [2] proposed a loopback interface (ism_lo), that can be used on non-s390 architectures (e.g. between containers or to test SMC-D). A minimal implementation went upstream with [3]: ism_lo currently is a part of the smc protocol and rather hidden. [4] proposed a virtio definition of ism (ism_virtio) that can be used between kvm guests. We will shortly send an RFC for an dibs client that uses dibs as transport for TTY. Concept: -------- Create a shim layer in net/dibs that contains common definitions and code for all dibs devices and all dibs clients. Any device or client module only needs to depend on this dibs layer module and any device or client code only needs to include the definitions in include/linux/dibs.h. The name dibs was chosen to clearly distinguish it from the existing s390 ism devices. And to emphasize that it is not about sharing whole memory regions with anybody, but dedicating single buffers for another system. Implementation: --------------- The end result of this series is: A dibs shim layer with - One dibs client: smc-d - Two dibs device drivers: ism and dibs-loopback - Everything prepared to add more clients and more device drivers. Patches 1-2 contain some issues that were found along the way. They make sense on their own, but also enable a better structured dibs series. There are three components that exist today: a) smc module (especially SMC-D functionality, which is an ism client today) b) ism device driver (supports multiple ism clients today) c) smc-loopback (integrated with smc today) In order to preserve existing functionality at each step, these are not moved to dibs layer by component, instead: - the dibs layer is established in parallel to existing code [patches 3-6] - then some service functions are moved to the dibs layer [patches 7-12] - the actual data movement is moved to the dibs layer [patch 13] - and last event handling is moved to the dibs layer [patch 14] Future: ------- Items that are not part of this patchset but can be added later: - dynamically add or remove dibs_loopback. That will be allow for simple testing of add_dev()/del_dev() - handle_irq(): Call clients without interrupt context. e.g using threaded interrupts. I left this for a follow-on, because it includes conceptual changes for the smcd receive code. - Any improvements of locking scopes. I mainly moved some of the the existing locks to dibs layer. I have the feeling there is room for improvements. - The device drivers should not loop through the client array - dibs_dev_op.*_dmb() functions reveal unnecessary details of the internal dmb struct to the clients - Check whether client calls to dibs_dev_ops should be replaced by interface functions that provide additional value - Check whether device driver calls to dibs_client_ops should be replaced by interface functions that provide additional value. Link: [1] https://netdevconf.info/0x19/sessions/talk/communication-via-internal-shared-memory-ism-time-to-open-up.html Link: [2] https://lore.kernel.org/netdev/1695568613-125057-1-git-send-email-guwen@linux.alibaba.com/ Link: [3] https://lore.kernel.org/linux-kernel//20240428060738.60843-1-guwen@linux.alibaba.com/ Link: [4] https://groups.oasis-open.org/communities/community-home/digestviewer/viewthread?GroupId=3973&MessageKey=c060ecf9-ea1a-49a2-9827-c92f0e6447b2&CommunityKey=2f26be99-3aa1-48f6-93a5-018dce262226&hlmlt=VT ==================== Link: https://patch.msgid.link/20250918110500.1731261-1-wintera@linux.ibm.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.