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Diffstat (limited to 'Documentation/powerpc/cxlflash.txt')
| -rw-r--r-- | Documentation/powerpc/cxlflash.txt | 63 |
1 files changed, 62 insertions, 1 deletions
diff --git a/Documentation/powerpc/cxlflash.txt b/Documentation/powerpc/cxlflash.txt index f943967f90ce..4202d1bc583c 100644 --- a/Documentation/powerpc/cxlflash.txt +++ b/Documentation/powerpc/cxlflash.txt @@ -163,7 +163,8 @@ DK_CXLFLASH_ATTACH - These tokens are only valid for the process under which they were created. The child of a forked process cannot continue - to use the context id or file descriptor created by its parent. + to use the context id or file descriptor created by its parent + (see DK_CXLFLASH_VLUN_CLONE for further details). - These tokens are only valid for the lifetime of the context and the process under which they were created. Once either is @@ -193,6 +194,45 @@ DK_CXLFLASH_USER_DIRECT treated as a resource handle that is returned to the user. The user is then able to use the handle to reference the LUN during I/O. +DK_CXLFLASH_USER_VIRTUAL +------------------------ + This ioctl is responsible for transitioning the LUN to virtual mode + of access and configuring the AFU for virtual access from user space + on a per-context basis. Additionally, the block size and last logical + block address (LBA) are returned to the user. + + As mentioned previously, when operating in user space access mode, + LUNs may be accessed in whole or in part. Only one mode is allowed + at a time and if one mode is active (outstanding references exist), + requests to use the LUN in a different mode are denied. + + The AFU is configured for virtual access from user space by adding + an entry to the AFU's resource handle table. The index of the entry + is treated as a resource handle that is returned to the user. The + user is then able to use the handle to reference the LUN during I/O. + + By default, the virtual LUN is created with a size of 0. The user + would need to use the DK_CXLFLASH_VLUN_RESIZE ioctl to adjust the grow + the virtual LUN to a desired size. To avoid having to perform this + resize for the initial creation of the virtual LUN, the user has the + option of specifying a size as part of the DK_CXLFLASH_USER_VIRTUAL + ioctl, such that when success is returned to the user, the + resource handle that is provided is already referencing provisioned + storage. This is reflected by the last LBA being a non-zero value. + +DK_CXLFLASH_VLUN_RESIZE +----------------------- + This ioctl is responsible for resizing a previously created virtual + LUN and will fail if invoked upon a LUN that is not in virtual + mode. Upon success, an updated last LBA is returned to the user + indicating the new size of the virtual LUN associated with the + resource handle. + + The partitioning of virtual LUNs is jointly mediated by the cxlflash + driver and the AFU. An allocation table is kept for each LUN that is + operating in the virtual mode and used to program a LUN translation + table that the AFU references when provided with a resource handle. + DK_CXLFLASH_RELEASE ------------------- This ioctl is responsible for releasing a previously obtained @@ -214,6 +254,27 @@ DK_CXLFLASH_DETACH success, all "tokens" which had been provided to the user from the DK_CXLFLASH_ATTACH onward are no longer valid. +DK_CXLFLASH_VLUN_CLONE +---------------------- + This ioctl is responsible for cloning a previously created + context to a more recently created context. It exists solely to + support maintaining user space access to storage after a process + forks. Upon success, the child process (which invoked the ioctl) + will have access to the same LUNs via the same resource handle(s) + and fd2 as the parent, but under a different context. + + Context sharing across processes is not supported with CXL and + therefore each fork must be met with establishing a new context + for the child process. This ioctl simplifies the state management + and playback required by a user in such a scenario. When a process + forks, child process can clone the parents context by first creating + a context (via DK_CXLFLASH_ATTACH) and then using this ioctl to + perform the clone from the parent to the child. + + The clone itself is fairly simple. The resource handle and lun + translation tables are copied from the parent context to the child's + and then synced with the AFU. + DK_CXLFLASH_VERIFY ------------------ This ioctl is used to detect various changes such as the capacity of |