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Diffstat (limited to 'Documentation/infiniband/user_verbs.txt')
| -rw-r--r-- | Documentation/infiniband/user_verbs.txt | 69 |
1 files changed, 0 insertions, 69 deletions
diff --git a/Documentation/infiniband/user_verbs.txt b/Documentation/infiniband/user_verbs.txt deleted file mode 100644 index 47ebf2f80b2b..000000000000 --- 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 pinned_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 pinned_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. |