Hi Dan, On 6/8/2021 4:03 AM, Dan Williams wrote:
On Wed, Jun 2, 2021 at 6:36 PM Jingqi Liu <[email protected]> wrote:The following bug is caused by setting the size of Label Index Block to a fixed 256 bytes. Use the following Qemu command to start a Guest with 2MB label-size: -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax1.1,size=14G,align=2M -device nvdimm,memdev=mem1,id=nv1,label-size=2M There is a namespace in the Guest as follows: $ ndctl list [ { "dev":"namespace0.0", "mode":"devdax", "map":"dev", "size":14780727296, "uuid":"58ad5282-5a16-404f-b8ee-e28b4c784eb8", "chardev":"dax0.0", "align":2097152, "name":"namespace0.0" } ] Fail to read labels. The result is as follows: $ ndctl read-labels -u nmem0 [ ] read 0 nmem If using the following Qemu command to start the Guest with 128K label-size, this label can be read correctly. -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax1.1,size=14G,align=2M -device nvdimm,memdev=mem1,id=nv1,label-size=128K The size of a Label Index Block depends on how many label slots fit into the label storage area. The minimum size of an index block is 256 bytes and the size must be a multiple of 256 bytes. For a storage area of 128KB, the corresponding Label Index Block size is 256 bytes. But if the label storage area is not 128KB, the Label Index Block size should not be 256 bytes. Namespace Label Index Block appears twice at the top of the label storage area. Following the two index blocks, an array for storing labels takes up the remainder of the label storage area. When reading namespace index and labels, we should read the field of 'mysize' in the Label Index Block. Then we can correctly calculate the starting offset of another Label Index Block and the following namespace labels.Good find! I agree this is broken, but I'm not sure this is the way to fix it. The ndctl enabling is meant to support dumping index blocks that might be corrupt, so I don't want to rely on index block data for this value. It should copy the kernel which has this definition for determining sizeof_namespace_index(): size_t sizeof_namespace_index(struct nvdimm_drvdata *ndd) { u32 nslot, space, size; /* * Per UEFI 2.7, the minimum size of the Label Storage Area is large * enough to hold 2 index blocks and 2 labels. The minimum index * block size is 256 bytes. The label size is 128 for namespaces * prior to version 1.2 and at minimum 256 for version 1.2 and later. */ nslot = nvdimm_num_label_slots(ndd); space = ndd->nsarea.config_size - nslot * sizeof_namespace_label(ndd); size = __sizeof_namespace_index(nslot) * 2; if (size <= space && nslot >= 2) return size / 2; dev_err(ndd->dev, "label area (%d) too small to host (%d byte) labels\n", ndd->nsarea.config_size, sizeof_namespace_label(ndd)); return 0; }
Good point. Thanks for your comment. I'll send a patch based on your suggestion soon. Thanks, Jingqi
