P. Hardware Error Record Persistence Usage¶
The OS determines if a platform implements support for Hardware Error Record Persistence by reading the HwErrRecSupport globally defined variable. If the attempt to read this variable returns EFI_NOT_FOUND (14), then the OS will infer that the platform does not implement Hardware Error Record Persistence. If the attempt to read this variable succeeds, then the OS uses the returned value to determine whether the platform supports Hardware Error Record Persistence. A non-zero value indicates that the platform supports Hardware Error Record Persistence.
P.1. Determining space¶
To determine the amount of space (in bytes) guaranteed by the platform for saving hardware error records, the OS invokes QueryVariableInfo, setting the HR bit in the Attributes bitmask.
P.2. Saving Hardware error records¶
To save a hardware error record, the OS invokes SetVariable, supplying EFI_HARDWARE_ERROR_VARIABLE as the VendorGuid and setting the HR bit in the Attributes bitmask. The VariableName will be constructed by the OS by concatenating an index to the string “HwErrRec” (i.e., HwErrRec0001). The index portion of the variable name is determined by reading all of the hardware error record variables currently stored on the platform and choosing an appropriate index value based on the names of the existing variables. The platform saves the supplied Data. If insufficient space is present to store the record, the platform will return EFI_OUT_OF_RESOURCES, in which case, the OS may clear an existing record and retry. A retry attempt may continue to fail with status EFI_OUT_OF_RESOURCES if a reboot is required to coalesce resources after deletion. The OS may only save error records after ExitBootServices is called. Firmware may also use the Hardware Error Record Persistence interface to write error records, but it may only do so before ExitBootServices is called. If firmware uses this interface to write an error record, it must use the VariableName format used by the OS as described above and the error records it creates must contain the firmware’s CreatorId. Firmware may overwrite error records whose CreatorId matches the firmware’s CreatorId. Firmware may overwrite error records that have been cleared by other components.
During OS initialization, the OS discovers the names of all persisted error record variables by enumerating the current variable names using GetNextVariableName. Having identified the names of all error record variables, the OS will then read and process all of the error records from the store. After the OS processes an error record, it clears the variable if it was the creator of the variable (determined by checking the CreatorId field of the error record).
P.3. Clearing error record variables¶
To clear error record variables, the OS invokes SetVariable, supplying EFI_HARDWARE_ERROR_VARIABLE as the VendorGuid and setting the HR bit in the Attributes bitmask. The supplied DataSize, and Data parameters will all be set to zero to indicate that the variable is to be cleared. The supplied VariableName identifies which error record variable is to be cleared. The OS may only clear error records after ExitBootServices has been called. The OS itself may only clear error records which it created (e.g. error records whose CreatorId matches that of the OS). However, a management application running on the OS may clear error records created by other components. This enables error records created by firmware or other OSes to be cleared by the currently running OS.