ndctl inject-error <namespace> [<options>]
Theory of Operation
The capacity of an NVDIMM REGION (contiguous span of persistent memory) is accessed via one or more NAMESPACE devices. REGION is the Linux term for what ACPI and UEFI call a DIMM-interleave-set, or a system-physical-address-range that is striped (by the memory controller) across one or more memory modules.
The UEFI specification defines the NVDIMM Label Protocol as the combination of label area access methods and a data format for provisioning one or more NAMESPACE objects from a REGION. Note that label support is optional and if Linux does not detect the label capability it will automatically instantiate a "label-less" namespace per region. Examples of label-less namespaces are the ones created by the kernel’s memmap=ss!nn command line option (see the nvdimm wiki on kernel.org), or NVDIMMs without a valid namespace index in their label area.
Label-less namespaces lack many of the features of their label-rich cousins. For example, their size cannot be modified, or they cannot be fully destroyed (i.e. the space reclaimed). A destroy operation will zero any mode-specific metadata. Finally, for create-namespace operations on label-less namespaces, ndctl bypasses the region capacity availability checks, and always satisfies the request using the full region capacity. The only reconfiguration operation supported on a label-less namespace is changing its mode.
A namespace can be provisioned to operate in one of 4 modes, fsdax, devdax, sector, and raw. Here are the expected usage models for these modes:
- fsdax: Filesystem-DAX mode is the default mode of a namespace when specifying ndctl create-namespace with no options. It creates a block device (/dev/pmemX[.Y]) that supports the DAX capabilities of Linux filesystems (xfs and ext4 to date). DAX removes the page cache from the I/O path and allows mmap(2) to establish direct mappings to persistent memory media. The DAX capability enables workloads / working-sets that would exceed the capacity of the page cache to scale up to the capacity of persistent memory. Workloads that fit in page cache or perform bulk data transfers may not see benefit from DAX. When in doubt, pick this mode.
- devdax: Device-DAX mode enables similar mmap(2) DAX mapping capabilities as Filesystem-DAX. However, instead of a block-device that can support a DAX-enabled filesystem, this mode emits a single character device file (/dev/daxX.Y). Use this mode to assign persistent memory to a virtual-machine, register persistent memory for RDMA, or when gigantic mappings are needed.
- sector: Use this mode to host legacy filesystems that do not checksum metadata or applications that are not prepared for torn sectors after a crash. Expected usage for this mode is for small boot volumes. This mode is compatible with other operating systems.
- raw: Raw mode is effectively just a memory disk that does not support DAX. Typically this indicates a namespace that was created by tooling or another operating system that did not know how to create a Linux fsdax or devdax mode namespace. This mode is compatible with other operating systems, but again, does not support DAX operation.
ndctl-inject-error can be used to ask the platform to simulate media errors in the NVDIMM address space to aid debugging and development of features related to error handling.
By default, injecting an error actually only injects an error to the first n bytes of the block, where n is the output of ndctl_cmd_ars_cap_get_size(). In other words, we only inject one ars_unit per sector. This is sufficient for Linux to mark the whole sector as bad, and will show up as such in the various badblocks lists in the kernel. If multiple blocks are being injected, only the first n bytes of each block specified will be injected as errors. This can be overridden by the --saturate option, which will force the entire block to be injected as an error.
These commands are DANGEROUS and can cause data loss. They are only provided for testing and debugging purposes.
Inject errors in namespace0.0 at block 12 for 2 blocks (i.e. 12, 13)
ndctl inject-error --block=12 --count=2 namespace0.0
Check status of injected errors on namespace0.0
ndctl inject-error --status namespace0.0
Uninject errors at block 12 for 2 blocks on namespace0.0
ndctl inject-error --uninject --block=12 --count=2 namespace0.0
- -B, --block=
Namespace block offset in 512 byte sized blocks where the error is to be injected.
NOTE: The offset is interpreted in different ways based on the "mode" of the namespace. For "raw" mode, the offset is the base namespace offset. For "fsdax" mode (i.e. a "pfn" namespace), the offset is relative to the user-visible part of the namespace, and the offset introduced by the kernel's metadata will be accounted for. For a "sector" mode namespace (i.e. a "BTT" namespace), the offset is relative to the base namespace, as the BTT translation details are internal to the kernel, and can't be accounted for while injecting errors.
- -n, --count=
Number of blocks to inject as errors. This is also in terms of fixed, 512 byte blocks.
- -d, --uninject
This option will ask the platform to remove any injected errors for the specified block offset, and count.
WARNING: This will not clear the kernel's internal badblock tracking, those can only be cleared by doing a write to the affected locations. Hence use the --clear option only if you know exactly what you are doing. For normal usage, injected errors should only be cleared by doing writes. Do not expect have the original data intact after injecting an error, and clearing it using --clear - it will be lost, as the only "real" way to clear the error location is to write to it or zero it (truncate/hole-punch).
- -t, --status
This option will retrieve the status of injected errors. Note that this will not retrieve all known/latent errors (i.e. non injected ones), and is NOT equivalent to performing an Address Range Scrub.
- -N, --no-notify
This option is only valid when injecting errors. By default, the error inject command and will ask platform firmware to trigger a notification in the kernel, asking it to update its state of known errors. With this option, the error will still be injected, the kernel will not get a notification, and the error will appear as a latent media error when the location is accessed. If the platform firmware does not support this feature, this will have no effect.
- -S, --saturate
This option forces error injection or un-injection to cover the entire address range covered by the specified block(s).
- -v, --verbose
Emit debug messages for the error injection process
- -u, --human
Format numbers representing storage sizes, or offsets as human readable strings with units instead of the default machine-friendly raw-integer data. Convert other numeric fields into hexadecimal strings.
- -r, --region=
A regionX device name, or a region id number. Restrict the operation to the specified region(s). The keyword all can be specified to indicate the lack of any restriction, however this is the same as not supplying a --region option at all.
- -b, --bus=
A bus id number, or a provider string (e.g. "ACPI.NFIT"). Restrict the operation to the specified bus(es). The keyword all can be specified to indicate the lack of any restriction, however this is the same as not supplying a --bus option at all.
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