Replace the existing Documentation/infiniband/user_verbs.txt with Documentation/infiniband/user_verbs.rst. No substantial changes to the content - just some minor reformatting to have the rendering come out nicely. This is in preparation for updating the content in a subsequent patch. Signed-off-by: Joel Nider <joeln@xxxxxxxxxx> --- Documentation/infiniband/user_verbs.rst | 70 +++++++++++++++++++++++++++++++++ Documentation/infiniband/user_verbs.txt | 69 -------------------------------- 2 files changed, 70 insertions(+), 69 deletions(-) create mode 100644 Documentation/infiniband/user_verbs.rst delete mode 100644 Documentation/infiniband/user_verbs.txt diff --git a/Documentation/infiniband/user_verbs.rst b/Documentation/infiniband/user_verbs.rst new file mode 100644 index 0000000..ffc4aec --- /dev/null +++ b/Documentation/infiniband/user_verbs.rst @@ -0,0 +1,70 @@ +====================== +Userspace Verbs Access +====================== +The ib_uverbs module, built by enabling CONFIG_INFINIBAND_USER_VERBS, +enables direct userspace access to IB hardware via "verbs," as +described in chapter 11 of the InfiniBand Architecture Specification. + +To use the verbs, the libibverbs library, available from +https://github.com/linux-rdma/rdma-core, is required. libibverbs contains a +device-independent API for using the ib_uverbs interface. +libibverbs also requires appropriate device-dependent kernel and +userspace driver for your InfiniBand hardware. For example, to use +a Mellanox HCA, you will need the ib_mthca kernel module and the +libmthca userspace driver be installed. + +User-kernel communication +========================= +Userspace communicates with the kernel for slow path, resource +management operations via the /dev/infiniband/uverbsN character +devices. Fast path operations are typically performed by writing +directly to hardware registers mmap()ed into userspace, with no +system call or context switch into the kernel. + +Commands are sent to the kernel via write()s on these device files. +The ABI is defined in drivers/infiniband/include/ib_user_verbs.h. +The structs for commands that require a response from the kernel +contain a 64-bit field used to pass a pointer to an output buffer. +Status is returned to userspace as the return value of the write() +system call. + +Resource management +=================== +Since creation and destruction of all IB resources is done by +commands passed through a file descriptor, the kernel can keep track +of which resources are attached to a given userspace context. The +ib_uverbs module maintains idr tables that are used to translate +between kernel pointers and opaque userspace handles, so that kernel +pointers are never exposed to userspace and userspace cannot trick +the kernel into following a bogus pointer. + +This also allows the kernel to clean up when a process exits and +prevent one process from touching another process's resources. + +Memory pinning +============== +Direct userspace I/O requires that memory regions that are potential +I/O targets be kept resident at the same physical address. The +ib_uverbs module manages pinning and unpinning memory regions via +get_user_pages() and put_page() calls. It also accounts for the +amount of memory pinned in the process's locked_vm, and checks that +unprivileged processes do not exceed their RLIMIT_MEMLOCK limit. + +Pages that are pinned multiple times are counted each time they are +pinned, so the value of locked_vm may be an overestimate of the +number of pages pinned by a process. + +/dev files +========== +To create the appropriate character device files automatically with +udev, a rule like:: + + KERNEL=="uverbs*", NAME="infiniband/%k" + +can be used. This will create device nodes named:: + + /dev/infiniband/uverbs0 + +and so on. Since the InfiniBand userspace verbs should be safe for +use by non-privileged processes, it may be useful to add an +appropriate MODE or GROUP to the udev rule. diff --git a/Documentation/infiniband/user_verbs.txt b/Documentation/infiniband/user_verbs.txt deleted file mode 100644 index df049b9..0000000 --- a/Documentation/infiniband/user_verbs.txt +++ /dev/null @@ -1,69 +0,0 @@ -USERSPACE VERBS ACCESS - - The ib_uverbs module, built by enabling CONFIG_INFINIBAND_USER_VERBS, - enables direct userspace access to IB hardware via "verbs," as - described in chapter 11 of the InfiniBand Architecture Specification. - - To use the verbs, the libibverbs library, available from - https://github.com/linux-rdma/rdma-core, is required. libibverbs contains a - device-independent API for using the ib_uverbs interface. - libibverbs also requires appropriate device-dependent kernel and - userspace driver for your InfiniBand hardware. For example, to use - a Mellanox HCA, you will need the ib_mthca kernel module and the - libmthca userspace driver be installed. - -User-kernel communication - - Userspace communicates with the kernel for slow path, resource - management operations via the /dev/infiniband/uverbsN character - devices. Fast path operations are typically performed by writing - directly to hardware registers mmap()ed into userspace, with no - system call or context switch into the kernel. - - Commands are sent to the kernel via write()s on these device files. - The ABI is defined in drivers/infiniband/include/ib_user_verbs.h. - The structs for commands that require a response from the kernel - contain a 64-bit field used to pass a pointer to an output buffer. - Status is returned to userspace as the return value of the write() - system call. - -Resource management - - Since creation and destruction of all IB resources is done by - commands passed through a file descriptor, the kernel can keep track - of which resources are attached to a given userspace context. The - ib_uverbs module maintains idr tables that are used to translate - between kernel pointers and opaque userspace handles, so that kernel - pointers are never exposed to userspace and userspace cannot trick - the kernel into following a bogus pointer. - - This also allows the kernel to clean up when a process exits and - prevent one process from touching another process's resources. - -Memory pinning - - Direct userspace I/O requires that memory regions that are potential - I/O targets be kept resident at the same physical address. The - ib_uverbs module manages pinning and unpinning memory regions via - get_user_pages() and put_page() calls. It also accounts for the - amount of memory pinned in the process's locked_vm, and checks that - unprivileged processes do not exceed their RLIMIT_MEMLOCK limit. - - Pages that are pinned multiple times are counted each time they are - pinned, so the value of locked_vm may be an overestimate of the - number of pages pinned by a process. - -/dev files - - To create the appropriate character device files automatically with - udev, a rule like - - KERNEL=="uverbs*", NAME="infiniband/%k" - - can be used. This will create device nodes named - - /dev/infiniband/uverbs0 - - and so on. Since the InfiniBand userspace verbs should be safe for - use by non-privileged processes, it may be useful to add an - appropriate MODE or GROUP to the udev rule. -- 2.7.4
